Financial Analysis

Note 2: Acquisitions Alcyone Therapeutics, Inc. In November 2025 we completed the acquisition of all of the issued and outstanding shares of Alcyone Therapeutics, Inc., a clinical-stage biotechnology company focused on pediatric care through precision CNS therapeutics and dosing platforms. Alcyone's lead asset is ThecaFlex DRx, an implantable subcutaneous port and catheter device being investigated for the intrathecal delivery of ASOs, including SPINRAZA, which is designed to provide an alternative to repeat lumbar punctures in chronic intrathecal administration of medicines. Total consideration for this transaction, which was recorded in acquired in-process research and development, upfront and milestone expense in our consolidated statements of income for the year ended December 31, 2025, was approximately $85.0 million, comprising a $50.0 million payment made upon closing and a $35.0 million payment that was considered probable as of December 31, 2025, and made upon FDA approval of a supplemental application in January 2026. We may pay additional development and regulatory milestone payments to the former shareholders of Alcyone of up to a total of $75.0 million if approval is received for ThecaFlex DRx administration of SPINRAZA or other additional pipeline products. We accounted for this transaction as an asset acquisition as the value being acquired primarily relates to a single asset. U nder the terms of this acquisition, we will oversee the end-to-end development, man …

BusinessCombinationDisclosureTextBlock · excerpt; the full note is in the filing

Note 22: Commitments and Contingencies Royalty Payments TYSABRI We are obligated to make contingent payments of 18.0% on annual worldwide net sales of TYSABRI up to $2.0 billion and 25.0% on annual worldwide net sales of TYSABRI that exceed $2.0 billion. Royalty payments are recognized as cost of sales in our consolidated statements of income. SPINRAZA We make royalty payments to Ionis on annual worldwide net sales of SPINRAZA using a tiered royalty rate between 11.0% and 15.0%, which are recognized in cost of sales within our consolidated statements of income. For additional information on our collaboration arrangements with Ionis, please read Note 19, Collaborative and Other Relationships , to these consolidated financial statements. QALSODY We make royalty payments to Ionis on annual worldwide net sales of QALSODY using a tiered royalty rate between 11.0% and 15.0%, which are recognized in cost of sales within our consolidated statements of income. For additional information on our collaboration arrangements with Ionis, please read Note 19, Collaborative and Other Relationships , to these consolidated financial statements. VUMERITY We make royalty payments to Alkermes on worldwide net sales of VUMERITY using a royalty rate of 15.0% on product that Alkermes has manufactured and 16.0% on product manufactured by us or a third-party designee, which are recognized as cost of sales in our consolidated statements of income. SKYCLARYS In connection with our acquisition of Reata in …

CommitmentsAndContingenciesDisclosureTextBlock · excerpt; the full note is in the filing

Note 13: Indebtedness Our indebtedness is summarized as follows: As of December 31, (In millions) 2025 2024 Current portion: 4.050% Senior Notes due September 15, 2025 $ $ 1,748.6 Current portion of notes payable $ $ 1,748.6 Non-current portion: 2.250% Senior Notes due May 1, 2030 $ 1,495.7 $ 1,494.7 5.050% Senior Notes due January 15, 2031 398.0 5.750% Senior Notes due May 15, 2035 645.5 5.200% Senior Notes due September 15, 2045 1,101.5 1,101.1 3.150% Senior Notes due May 1, 2050 1,475.6 1,475.0 3.250% Senior Notes due February 15, 2051 480.3 476.4 6.450% Senior Notes due May 15, 2055 690.2 Non-current portion of notes payable $ 6,286.8 $ 4,547.2 As of December 31, 2025, we were in compliance with our senior note covenants. 2025 Senior Notes On May 12, 2025, we issued senior unsecured notes for an aggregate principal amount of $1.75 billion, consisting of the following: $400.0 million of 5.050% Senior Notes due January 15, 2031, valued at 99.981% of par; $650.0 million of 5.750% Senior Notes due May 15, 2035, valued at 99.924% of par; and $700.0 million of 6.450% Senior Notes due May 15, 2055, valued at 99.657% of par. Our 2025 Senior Notes are senior unsecured obligations and may be redeemed at our option at any time at 100% of the principal amount plus accrued interest and, until a specified period before maturity, a specified make-whole amount. Our 2025 Senior Notes contain a change-of-control provision that, under certain circumstances, may require us to purchase our 20 …

DebtDisclosureTextBlock · excerpt; the full note is in the filing

Revenue by product are summarized as follows: For the Years Ended December 31, 2025 2024 2023 (In millions) United States Rest of World Total United States Rest of World Total United States Rest of World Total Multiple Sclerosis: TECFIDERA $ 168.5 $ 511.2 $ 679.7 $ 169.2 $ 797.9 $ 967.1 $ 263.1 $ 749.4 $ 1,012.5 VUMERITY 651.2 95.6 746.8 538.6 89.4 628.0 512.1 64.2 576.3 Total Fumarate 819.7 606.8 1,426.5 707.8 887.3 1,595.1 775.2 813.6 1,588.8 AVONEX 482.9 212.6 695.5 451.3 256.2 707.5 536.7 274.3 811.0 PLEGRIDY 104.9 145.2 250.1 111.4 149.1 260.5 126.2 168.5 294.7 Total Interferon 587.8 357.8 945.6 562.7 405.3 968.0 662.9 442.8 1,105.7 TYSABRI 965.0 700.4 1,665.4 920.0 795.0 1,715.0 997.9 879.0 1,876.9 FAMPYRA (1) 1.4 1.4 71.7 71.7 90.5 90.5 Subtotal: Multiple Sclerosis 2,372.5 1,666.4 4,038.9 2,190.5 2,159.3 4,349.8 2,436.0 2,225.9 4,661.9 Rare Disease: SPINRAZA 625.5 921.3 1,546.8 625.7 947.5 1,573.2 610.5 1,130.7 1,741.2 SKYCLARYS (2) 310.6 209.9 520.5 301.1 81.4 382.5 55.9 55.9 QALSODY (3) 30.1 56.8 86.9 20.9 11.5 32.4 5.8 0.1 5.9 Subtotal: Rare Disease 966.2 1,188.0 2,154.2 947.7 1,040.4 1,988.1 672.2 1,130.8 1,803.0 Biosimilars: BENEPALI 453.2 453.2 479.1 479.1 438.8 438.8 IMRALDI 190.2 190.2 213.1 213.1 222.1 222.1 FLIXABI 52.6 52.6 63.2 63.2 77.4 77.4 BYOOVIZ 13.0 19.4 32.4 23.0 13.6 36.6 29.2 2.5 31.7 TOFIDENCE 0.7 0.7 1.1 1.1 Subtotal: Biosimilars 13.7 715.4 729.1 24.1 769.0 793.1 29.2 740.8 770.0 Other: ZURZUVAE 195.1 195.1 72.2 72.2 1.6 1.6 Other (4) 0.4 1.7 2.1 …

DisaggregationOfRevenueTableTextBlock · excerpt; the full note is in the filing

Note 16: Share-Based Payments Share-Based Compensation Expense The following table summarizes share-based compensation expense included in our consolidated statements of income: For the Years Ended December 31, (In millions) 2025 2024 2023 Research and development $ 115.7 $ 154.1 $ 296.7 Selling, general and administrative 187.8 198.6 371.7 Subtotal 303.5 352.7 668.4 Capitalized share-based compensation costs (12.4) (10.3) (10.2) Share-based compensation expense included in total cost and expense 291.1 342.4 658.2 Income tax effect (57.0) (63.4) (132.6) Share-based compensation expense included in net income attributable to Biogen Inc. $ 234.1 $ 279.0 $ 525.6 In connection with our acquisition of HI-Bio in July 2024 we recognized HI-Bio equity-based compensation expense, inclusive of employer taxes, of approximately $56.4 million attributable to the post-acquisition service period, of which $42.5 million was recognized as a charge to research and development expense with the remaining $13.9 million as a charge to selling, general and administrative expense within our consolidated statements of income for the year ended December 31, 2024. These amounts were associated with the accelerated vesting of stock options and RSUs previously granted to HI-Bio employees and required no future services to vest. In connection with our acquisition of Reata in September 2023 we recognized Reata equity-based compensation expense, inclusive of employer taxes, of approximately $393.4 million a …

DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock · excerpt; the full note is in the filing

Note 8: Fair Value Measurements The tables below present information about our assets and liabilities that are regularly measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques we utilized to determine such fair value: Fair Value Measurements on a Recurring Basis As of December 31, 2025 (In millions) Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Cash equivalents $ 2,233.2 $ $ 2,233.2 $ Marketable debt securities: Corporate debt securities 537.6 537.6 Government securities 648.8 648.8 Mortgage and other asset backed securities 52.7 52.7 Marketable equity securities 118.1 118.1 Other current assets: Derivative contracts 10.0 10.0 Other non-current assets: Convertible notes (1) 35.0 35.0 Plan assets for deferred compensation 52.2 52.2 Derivative contracts 0.4 0.4 Total $ 3,688.0 $ 118.1 $ 3,534.9 $ 35.0 Liabilities: Other current liabilities: Derivative contracts $ 56.7 $ $ 56.7 $ Other non-current liabilities: Derivative contracts 2.2 2.2 Contingent consideration obligations 246.4 246.4 Total $ 305.3 $ $ 58.9 $ 246.4 (1) Convertible notes includes a $30.0 million convertible note we invested in as part of our strategic research arrangement with City Therapeutics during 2025, as well as a $5.0 million convertible note we invested into Neela Therapeutics, Inc. during 2025. We elected the fair value option for both converti …

FairValueDisclosuresTextBlock · excerpt; the full note is in the filing

Note 7: Intangible Assets and Goodwill Intangible Assets Intangible assets, net of accumulated amortization, impairment charges and adjustments are summarized as follows: As of December 31, 2025 As of December 31, 2024 (In millions) Estimated Life Cost Accumulated Amortization Net Cost Accumulated Amortization Net Completed technology 1-30 years $ 14,067.3 $ (6,687.8) $ 7,379.5 $ 14,138.4 $ (6,254.1) $ 7,884.3 In-process research and development Indefinite until commercialization 1,635.0 1,635.0 1,642.9 1,642.9 Priority review voucher Indefinite 100.0 100.0 100.0 100.0 Trademarks and trade names Indefinite 64.0 64.0 64.0 64.0 Total intangible assets $ 15,866.3 $ (6,687.8) $ 9,178.5 $ 15,945.3 $ (6,254.1) $ 9,691.2 Amortization and Impairments Amortization and impairment of acquired intangible assets totaled $515.0 million, $446.7 million and $240.6 million for the years ended December 31, 2025, 2024 and 2023, respectively. Amortization of acquired intangible assets, excluding impairment charges, totaled $507.1 million, $386.5 million and $240.6 million for the years ended December 31, 2025, 2024 and 2023, respectively. The increase in amortization of acquired intangible assets, excluding impairment charges, was primarily due to amortization for the acquired intangible assets associated with SKYCLARYS and TYSABRI. For the year ended December 31, 2025, amortization and impairment of acquired intangible assets reflects the impact of $7.9 million in impairment charges related to …

GoodwillAndIntangibleAssetsDisclosureTextBlock · excerpt; the full note is in the filing

"Note 17: Income Taxes Income Tax Expense Income before income tax (benefit) expense and the income tax (benefit) expense consist of the following: For the Years Ended December 31, (In millions) 2025 2024 2023 Income before income tax (benefit) expense: Domestic $ 1,225.2 $ 853.4 $ 192.4 Foreign 331.3 1,052.6 1,104.4 Total income before income tax (benefit) expense $ 1,556.5 $ 1,906.0 $ 1,296.8 Income tax (benefit) expense: Current: Federal $ 10.1 $ 448.9 $ 377.6 State 47.3 50.5 15.1 Foreign (155.4) (67.5) 48.4 Total current (98.0) 431.9 441.1 Deferred: Federal 346.1 (154.5) (587.4) State (25.1) (17.3) (12.7) Foreign 40.6 13.7 294.3 Total deferred 361.6 (158.1) (305.8) Total income tax (benefit) expense $ 263.6 $ 273.8 $ 135.3 The lower Federal current provision in 2025 reflects the impact of a tax deduction for certain previously deferred capitalized research and development expenditures under the OBBBA and the impact of recording a capital loss on our sale of Sage common stock. Foreign current benefit reflects the non-cash benefit of current year valuation allowance changes. Transition Toll Tax The Tax Cuts and Jobs Act of 2017 eliminated the deferral of U.S. income tax on the historical unrepatriated earnings by imposing the one-time mandatory deemed repatriation tax on accumulated foreign subsidiaries' previously untaxed foreign earnings. The Transition Toll Tax was assessed on our share of our foreign corporations' accumulated foreign earnings that were not previously ta …

IncomeTaxDisclosureTextBlock · excerpt; the full note is in the filing

"Note 21: Litigation We are currently involved in various claims, investigations and legal proceedings, including the matters described below. For information as to our accounting policies relating to claims and legal proceedings, including use of estimates and contingencies, please read Note 1, Summary of Significant Accounting Policies , to these consolidated financial statements. With respect to some loss contingencies, an estimate of the possible loss or range of loss cannot be made until management has further information, including, for example, (i) which claims, if any, will survive dispositive motion practice; (ii) information to be obtained through discovery; (iii) information as to the parties' damages claims and supporting evidence; (iv) the parties legal theories; and (v) the parties' settlement positions. If an estimate of the possible loss or range of loss can be made at this time, it is included in the potential loss contingency description below. The claims and legal proceedings in which we are involved also include challenges to the scope, validity or enforceability of the patents relating to our products, pipeline or processes and challenges to the scope, validity or enforceability of the patents held by others. These include claims by third parties that we infringe their patents. An adverse outcome in any of these proceedings could result in one or more of the following and have a material impact on our business or consolidated results of operations and fin …

LegalMattersAndContingenciesTextBlock · excerpt; the full note is in the filing

Note 12: Leases We lease real estate, including laboratory and office space, and certain equipment. Our leases have remaining lease terms ranging from less than one year to twenty-two years. Certain leases include one or more options to renew, exercised at our sole discretion, with renewal terms that can extend the lease term from less than one year to fifteen years. In addition, we sublease certain real estate to third parties. Our sublease portfolio consists of operating leases, with remaining lease terms ranging from three years to four years. All of our leases qualify as operating leases. The following table summarizes the presentation in our consolidated balance sheets of our operating leases: As of December 31, (In millions) Balance sheet location 2025 2024 Assets: Operating lease assets Operating lease assets $ 265.4 $ 356.4 Liabilities Current operating lease liabilities Accrued expense and other $ 80.4 $ 86.4 Non-current operating lease liabilities Long-term operating lease liabilities 290.4 334.5 Total operating lease liabilities $ 370.8 $ 420.9 The following table summarizes the effect of lease costs in our consolidated statements of income: For the Years Ended December 31, (In millions) Income Statement Location 2025 2024 2023 Operating lease cost Research and development $ 0.9 $ 2.4 $ 2.0 Selling, general and administrative 100.7 110.1 128.1 Variable lease cost Research and development 0.1 0.4 0.5 Selling, general and administrative 34.5 31.2 37.3 Sublease income …

LesseeOperatingLeasesTextBlock · excerpt; the full note is in the filing

New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that we adopt as of the specified effective date. Unless otherwise discussed below, we do not believe that the adoption of recently issued standards have or may have a material impact on our consolidated financial statements or disclosures. Standard Description Effective Date Effects on the Financial Statements ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures This standard establishes incremental disaggregation of income tax disclosures pertaining to the effective tax rate reconciliation and income taxes paid. The amendments in this update are required to be applied on a prospective basis with the option to apply it retrospectively. Annual reporting for fiscal years beginning after December 15, 2024. Early adoption is permitted. We adopted this standard and applied the disclosure requirements on a prospective basis effective for the year ended December 31, 2025. The adoption did not have a material impact on our consolidated financial position or results of operations. Refer to Note 17, Income Taxes , for our updated income tax disclosure. ASU No. 2024-03, Income Statement (Subtopic 220-40): Reporting Comprehensive Income - Expense Disaggregation Disclosures This standard requires disclosure in the notes to the financial statements, at each interim and annual reporting period, of specified information about cer …

NewAccountingPronouncementsPolicyPolicyTextBlock · excerpt; the full note is in the filing

Note 24: Employee Benefit Plans We sponsor various retirement and pension plans. Our estimates of liabilities and expense for these plans incorporate a number of assumptions, including expected rates of return on plan assets and interest rates used to discount future benefits. 401(k) Savings Plan We maintain a 401(k) Savings Plan, which is available to substantially all regular employees in the U.S. over the age of 21. Participants may make voluntary contributions. We make matching contributions according to the 401(k) Savings Plans matching formula. All matching contributions and participant contributions vest immediately. The 401(k) Savings Plan also holds certain transition contributions on behalf of participants who previously participated in the Biogen, Inc. Retirement Plan. The expense related to our 401(k) Savings Plan primarily consists of our matching contributions. Expense related to our 401(k) Savings Plan totaled approximately $52.6 million, $51.5 million and $55.9 million for the years ended December 31, 2025, 2024 and 2023, respectively. Deferred Compensation Plan We maintain a non-qualified deferred compensation plan, known as the SSP, which allows a select group of management employees in the U.S. to defer a portion of their compensation. The SSP also provides certain credits to highly compensated U.S. employees that are paid by the company. These credits are known as the Restoration Match. The deferred compensation amounts are accrued when earned. Such deferr …

PensionAndOtherPostretirementBenefitsDisclosureTextBlock · excerpt; the full note is in the filing

Note 4: Restructuring 2023 Fit for Growth Restructuring Program In 2023 we initiated cost saving measures as part of our Fit for Growth program to reduce operating costs, while improving operating efficiency and effectiveness. The Fit for Growth program generated approximately $1.0 billion in gross operating expense savings by the end of 2025, some of which has been reinvested in various initiatives. The Fit for Growth program included net headcount reductions of approximately 1,400 employees and we incurred total restructuring charges of approximately $320.0 million by the end of 2025. Total charges incurred from our 2023 Fit for Growth program are summarized as follows: For the Years Ended December 31, 2025 2024 2023 (In millions) Severance Costs Accelerated Depreciation and Other Total Severance Costs Accelerated Depreciation and Other Total Severance Costs Accelerated Depreciation and Other Total Selling, general and administrative $ $ (1.4) $ (1.4) $ $ 13.8 $ 13.8 $ $ 23.3 $ 23.3 Research and development 10.1 10.1 11.7 11.7 1.2 1.2 Restructuring charges 48.7 48.7 24.2 24.2 153.4 34.6 188.0 Total charges $ 48.7 $ 8.7 $ 57.4 $ 24.2 $ 25.5 $ 49.7 $ 153.4 $ 59.1 $ 212.5 Other Costs: Includes costs associated with items such as asset abandonment and write-offs, facility closure costs, pre-tax gains and losses resulting from the termination of certain leases, employee non-severance expense, consulting fees and other costs. Reata Integration Following the close of our Reata acq …

RestructuringAndRelatedActivitiesDisclosureTextBlock · excerpt; the full note is in the filing

Note 5: Revenue Product Revenue Revenue by product are summarized as follows: For the Years Ended December 31, 2025 2024 2023 (In millions) United States Rest of World Total United States Rest of World Total United States Rest of World Total Multiple Sclerosis: TECFIDERA $ 168.5 $ 511.2 $ 679.7 $ 169.2 $ 797.9 $ 967.1 $ 263.1 $ 749.4 $ 1,012.5 VUMERITY 651.2 95.6 746.8 538.6 89.4 628.0 512.1 64.2 576.3 Total Fumarate 819.7 606.8 1,426.5 707.8 887.3 1,595.1 775.2 813.6 1,588.8 AVONEX 482.9 212.6 695.5 451.3 256.2 707.5 536.7 274.3 811.0 PLEGRIDY 104.9 145.2 250.1 111.4 149.1 260.5 126.2 168.5 294.7 Total Interferon 587.8 357.8 945.6 562.7 405.3 968.0 662.9 442.8 1,105.7 TYSABRI 965.0 700.4 1,665.4 920.0 795.0 1,715.0 997.9 879.0 1,876.9 FAMPYRA (1) 1.4 1.4 71.7 71.7 90.5 90.5 Subtotal: Multiple Sclerosis 2,372.5 1,666.4 4,038.9 2,190.5 2,159.3 4,349.8 2,436.0 2,225.9 4,661.9 Rare Disease: SPINRAZA 625.5 921.3 1,546.8 625.7 947.5 1,573.2 610.5 1,130.7 1,741.2 SKYCLARYS (2) 310.6 209.9 520.5 301.1 81.4 382.5 55.9 55.9 QALSODY (3) 30.1 56.8 86.9 20.9 11.5 32.4 5.8 0.1 5.9 Subtotal: Rare Disease 966.2 1,188.0 2,154.2 947.7 1,040.4 1,988.1 672.2 1,130.8 1,803.0 Biosimilars: BENEPALI 453.2 453.2 479.1 479.1 438.8 438.8 IMRALDI 190.2 190.2 213.1 213.1 222.1 222.1 FLIXABI 52.6 52.6 63.2 63.2 77.4 77.4 BYOOVIZ 13.0 19.4 32.4 23.0 13.6 36.6 29.2 2.5 31.7 TOFIDENCE 0.7 0.7 1.1 1.1 Subtotal: Biosimilars 13.7 715.4 729.1 24.1 769.0 793.1 29.2 740.8 770.0 Other: ZURZUVAE 195.1 195.1 72.2 72 …

RevenueFromContractWithCustomerTextBlock · excerpt; the full note is in the filing

Note 25: Segment Information We operate and are managed as one operating segment, and derive revenue from activities related to the discovery, development and delivery of innovative therapies for people living with serious and complex diseases. Our research and development organization is responsible for the research and discovery of new product candidates and supports development and registration efforts for potential future products. Our pharmaceutical, operations and technology organization manages the development of the manufacturing processes, clinical trial supply, commercial product supply, distribution, buildings and facilities. Our commercial organization is responsible for U.S. and international development of our commercial products. We are also supported by corporate staff functions. Our CEO, as the CODM, manages and allocates resources to the operations of our company on a total company basis by assessing the overall level of resources available and deciding how to best deploy these resources across functions, therapeutic areas and research and development projects that are in line with our long-term company-wide strategic goals. In making these decisions, our CEO is provided with and uses consolidated financial information for purposes of evaluating performance, forecasting future period financial results, allocating resources and setting incentive targets. The CODM performs this assessment based on the segments net income. Through this analysis, which includes …

SegmentReportingDisclosureTextBlock · excerpt; the full note is in the filing

"Note 1: Summary of Significant Accounting Policies References in these notes to ""Biogen,"" the ""company,"" ""we,"" ""us"" and ""our"" refer to Biogen Inc. and its consolidated subsidiaries. Business Overview Biogen is a global biopharmaceutical company focused on discovering, developing and delivering innovative therapies for people living with serious and complex diseases. We have a broad portfolio of medicines to treat MS, have introduced the first approved treatment for SMA, co-developed treatments to address a defining pathology of Alzheimers disease and launched the first approved treatment to target a genetic cause of ALS. We market the first and only drug approved in the U.S., the E.U. and certain international markets for the treatment of FA in adults and adolescents aged 16 years and older. We are focused on advancing our pipeline in neurology, specialized immunology and rare diseases. We support our drug discovery and development efforts through internal research and development programs, external collaborations and acquisitions. Our marketed products include VUMERITY, TYSABRI, TECFIDERA, AVONEX and PLEGRIDY for the treatment of MS; SPINRAZA for the treatment of SMA; SKYCLARYS for the treatment of FA; and QALSODY for the treatment of ALS. We also have collaborations with Eisai on the commercialization of LEQEMBI for the treatment of Alzheimer's disease and Supernus on the commercialization of ZURZUVAE for the treatment of PPD. We have certain business and financi …

SignificantAccountingPoliciesTextBlock · excerpt; the full note is in the filing

Note 14: Equity Preferred Stock We have 8.0 million shares of Preferred Stock authorized, of which 1.75 million shares are authorized as Series A, 1.0 million shares are authorized as Series X junior participating and 5.25 million shares are undesignated. Shares may be issued without a vote or action of shareholders from time to time in classes or series with the designations, powers, preferences and the relative, participating, optional or other special rights of the shares of each such class or series and any qualifications, limitations or restrictions thereon as set forth in the instruments governing such shares. Any such Preferred Stock may rank prior to common stock as to dividend rights, liquidation preference or both, and may have full or limited voting rights and may be convertible into shares of common stock. No shares of Preferred Stock were issued and outstanding during 2025, 2024 and 2023. Common Stock The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2025, 2024 and 2023: As of December 31, 2025 As of December 31, 2024 As of December 31, 2023 (In millions) Authorized Issued Outstanding Authorized Issued Outstanding Authorized Issued Outstanding Common stock 1,000.0 170.5 146.8 1,000.0 169.5 145.8 1,000.0 168.7 144.9 Share Repurchases In October 2020 our Board of Directors authorized our 2020 Share Repurchase Program, which is a program to repurchase up to $5.0 billion of our common stock. O …

StockholdersEquityNoteDisclosureTextBlock · excerpt; the full note is in the filing

Note 2: Acquisitions Apellis Pharmaceuticals, Inc. On May 14, 2026, we completed the acquisition of all of the issued and outstanding shares of Apellis, a commercial-stage biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutic compounds to treat diseases with high unmet needs. As a result of this acquisition we acquired two FDA-approved products from Apellis: SYFOVRE (pegcetacoplan injection) for the treatment of GA, an immune-mediated retinal disease; and EMPAVELI (pegcetacoplan) for the treatment of PNH, a rare blood disorder, and C3G and primary IC-MPGN, rare immune-mediated kidney diseases. The addition of Apellis is expected to enhance our short- and long-term revenue growth profile by adding two commercialized, differentiated, specialized immunology products to our growth portfolio. Under the terms of this acquisition, Apellis shareholders were entitled to$41.00in cash for each issued and outstanding Apellis share, which totaled approximately $5.3 billion, and one contractual, non-transferable contingent value right per share representing the right to receive contingent cash payments of up to an aggregate of $4.00 per share in cash, subject to the achievement of specified annual global net sales thresholds for SYFOVRE. In addition, the total purchase price included approximately $70.7 million of future consideration attributable to pre-acquisition services. We funded this acquisition of Apellis with available cash and …

BusinessCombinationDisclosureTextBlock · excerpt; the full note is in the filing

Note 12: Indebtedness 2026 Term Loan Credit Agreement In connection with our acquisition of Apellis we entered into a $2.0 billion term loan credit agreement. On the closing date of the Apellis acquisition we drew $2.0 billion from the 2026 Term Loan, comprised of a $1.0 billion floating rate 364-day tranche and a $1.0 billion floating rate two-year tranche. As of June 30, 2026, we had $1.8 billion outstanding under the term loan credit agreement, of which $800.0 million was outstanding under the 364-day tranche and $1.0 billion outstanding under the two-year tranche. 2025 Senior Notes On May 12, 2025, we issued senior unsecured notes for an aggregate principal amount of $1.75 billion, consisting of the following: $400.0 million of 5.050% Senior Notes due January 15, 2031, valued at 99.981% of par; $650.0 million of 5.750% Senior Notes due May 15, 2035, valued at 99.924% of par; and $700.0 million of 6.450% Senior Notes due May 15, 2055, valued at 99.657% of par. Our 2025 Senior Notes are senior unsecured obligations and may be redeemed at our option at any time at 100% of the principal amount plus accrued interest and, until a specified period before maturity, a specified make-whole amount. Our 2025 Senior Notes contain a change-of-control provision that, under certain circumstances, may require us to purchase our 2025 Senior Notes at a price equal to 101% of the principal amount plus accrued and unpaid interest to the date of repurchase. We incurred approximately $13.9 mill …

DebtDisclosureTextBlock · excerpt; the full note is in the filing

Revenue by product is summarized as follows: For the Three Months Ended June 30, 2026 2025 (In millions) United States Rest of World Total United States Rest of World Total Multiple Sclerosis: TECFIDERA $ 32.4 $ 58.5 $ 90.9 $ 47.2 $ 146.4 $ 193.6 VUMERITY 172.0 24.5 196.5 188.0 24.3 212.3 Total Fumarate 204.4 83.0 287.4 235.2 170.7 405.9 AVONEX 120.9 49.1 170.0 121.7 56.0 177.7 PLEGRIDY 25.2 29.9 55.1 28.3 40.7 69.0 Total Interferon 146.1 79.0 225.1 150.0 96.7 246.7 TYSABRI 270.5 180.3 450.8 272.2 182.4 454.6 Subtotal: Multiple Sclerosis 621.0 342.3 963.3 657.4 449.8 1,107.2 Rare Disease: SPINRAZA 204.3 197.6 401.9 149.3 243.4 392.7 SKYCLARYS 82.3 85.6 167.9 78.0 52.3 130.3 QALSODY 8.3 23.6 31.9 7.5 12.5 20.0 Subtotal: Rare Disease 294.9 306.8 601.7 234.8 308.2 543.0 Specialized Immunology: SYFOVRE (1) 97.4 97.4 EMPAVELI (1) 30.4 30.4 Subtotal: Specialized Immunology 127.8 127.8 Biosimilars: BENEPALI 106.8 106.8 112.1 112.1 IMRALDI 37.8 37.8 46.7 46.7 FLIXABI 8.1 8.1 14.3 14.3 BYOOVIZ (2) 0.1 0.1 2.5 6.1 8.6 Subtotal: Biosimilars 0.1 152.7 152.8 2.5 179.2 181.7 Other: ZURZUVAE 70.7 0.1 70.8 46.4 46.4 Other (3) 0.4 0.4 Subtotal: Other 70.7 0.1 70.8 46.4 0.4 46.8 Total product revenue, net $ 1,114.5 $ 801.9 $ 1,916.4 $ 941.1 $ 937.6 $ 1,878.7 (1) EMPAVELI and SYFOVRE were obtained as part of our acquisition of Apellis in May 2026. (2) In the fourth quarter of 2025 we completed the sale of our rights to BYOOVIZ. (3) Other includes FUMADERM. For the Six Months Ended June 30, 2026 …

DisaggregationOfRevenueTableTextBlock · excerpt; the full note is in the filing

Note 15: Share-Based Payments Share-based Compensation Expense The following table summarizes share-based compensation expense included in our condensed consolidated statements of income: For the Three Months Ended June 30, For the Six Months Ended June 30, (In millions) 2026 2025 2026 2025 Research and development $ 32.3 $ 30.1 $ 67.1 $ 62.2 Selling, general and administrative 48.0 48.0 101.0 100.0 Subtotal 80.3 78.1 168.1 162.2 Capitalized share-based compensation costs (3.0) (3.2) (6.8) (6.3) Share-based compensation expense included in total cost and expense 77.3 74.9 161.3 155.9 Income tax effect (15.2) (14.9) (31.7) (30.9) Share-based compensation expense included in net income attributable to Biogen Inc. $ 62.1 $ 60.0 $ 129.6 $ 125.0 The following table summarizes share-based compensation expense associated with each of our share-based compensation programs: For the Three Months Ended June 30, For the Six Months Ended June 30, (In millions) 2026 2025 2026 2025 Time-vested restricted stock units $ 66.6 $ 60.6 $ 137.5 $ 126.7 Performance stock units settled in stock 11.8 15.0 25.1 28.6 Employee stock purchase plan 1.9 1.6 5.5 5.1 Stock options 0.9 1.8 Subtotal 80.3 78.1 168.1 162.2 Capitalized share-based compensation costs (3.0) (3.2) (6.8) (6.3) Share-based compensation expense included in total cost and expense $ 77.3 $ 74.9 $ 161.3 $ 155.9 …

DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock · excerpt; the full note is in the filing

Note 8: Fair Value Measurements The tables below present information about our assets and liabilities that are regularly measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques we utilized to determine such fair value: Fair Value Measurements on a Recurring Basis As of June 30, 2026 (In millions) Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Cash equivalents $ 569.4 $ $ 569.4 $ Marketable equity securities 184.0 184.0 Other current assets: Derivative contracts 21.6 21.6 Other non-current assets: Convertible notes (1) 35.0 35.0 Plan assets for deferred compensation 64.2 64.2 Derivative contracts 7.7 7.7 Total $ 881.9 $ 184.0 $ 662.9 $ 35.0 Liabilities: Other current liabilities: Derivative contracts $ 26.6 $ $ 26.6 $ Other non-current liabilities: Contingent consideration obligations 273.5 273.5 Total $ 300.1 $ $ 26.6 $ 273.5 (1) Convertible notes includes a $30.0 million convertible note we invested in City Therapeutics as part of our strategic research arrangement with the company during 2025, as well as a $5.0 million convertible note we invested into Neela Therapeutics, Inc. during 2025. We elected the fair value option for both convertible notes. For additional information on the arrangement with City Therapeutics, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements …

FairValueDisclosuresTextBlock · excerpt; the full note is in the filing

Note 7: Intangible Assets and Goodwill Intangible Assets Intangible assets, net of accumulated amortization, impairment charges and adjustments are summarized as follows: As of June 30, 2026 As of December 31, 2025 (In millions) Estimated Life Cost Accumulated Amortization Net Cost Accumulated Amortization Net Completed technology 1-30 years $ 18,708.8 $ (6,992.4) $ 11,716.4 $ 14,067.3 $ (6,687.8) $ 7,379.5 In-process research and development Indefinite until commercialization 1,636.0 1,636.0 1,635.0 1,635.0 Priority review voucher Indefinite 100.0 100.0 100.0 100.0 Trademarks and trade names Indefinite 64.0 64.0 64.0 64.0 Total intangible assets $ 20,508.8 $ (6,992.4) $ 13,516.4 $ 15,866.3 $ (6,687.8) $ 9,178.5 Amortization and Impairments For the three and six months ended June 30, 2026, amortization and impairment of acquired intangible assets totaled $168.2 million and $304.7 million, compared to $130.9 million and $242.7 million, respectively, in the prior year comparative periods. For the three and six months ended June 30, 2026, amortization of acquired intangible assets, excluding impairment charges, totaled $168.2 million and $304.7 million, respectively, compared to $127.4 million and $239.2 million, respectively in the prior year comparative per iods. The increases were primarily due to higher rates of amortization for the acquired intangible assets associated with SKYCLARYS. Additionally, we recorded $22.6 million of amortization for the acquired intangible assets …

GoodwillAndIntangibleAssetsDisclosureTextBlock · excerpt; the full note is in the filing

Note 16: Income Taxes Tax Rate For the three and six months ended June 30, 2026, our effective tax rate was 26.4% and 18.3%, respectively, compared to 14.7% and 17.0%, respectively, in the prior year comparative periods. The increase in our effective tax rate for the three months ended June 30, 2026 was primarily driven by non-deductible expenses related to our Apellis acquisition and, to a lesser extent, the favorable deferred tax impacts of decreases in foreign withholding taxes recorded in the second quarter of 2025. The six months ended June 30, 2026, compared to the same period in 2025, also reflects favorable impacts of a current year settlement of a foreign tax audit and the vesting of certain share-based awards. Accounting for Uncertainty in Income Taxes We and our subsidiaries are routinely examined by various taxing authorities. We file income tax returns in various U.S. states and in U.S. federal and other foreign jurisdictions. With few exceptions, we are no longer subject to U.S. federal tax examination for years before 2022 or state, local or non-U.S. income tax examinations for years before 2013. It is reasonably possible that we will adjust the value of our uncertain tax positions related to certain transfer pricing, collaboration matters, withholding taxes and other issues as we receive additional information from various taxing authorities, including reaching settlements with such authorities. For additional information on our income taxes, please read Note …

IncomeTaxDisclosureTextBlock · excerpt; the full note is in the filing

"Note 20: Litigation We are currently involved in various claims, investigations and legal proceedings, including the matters described below. For information as to our accounting policies relating to claims and legal proceedings, including use of estimates and contingencies, please read Note 1, Summary of Significant Accounting Policies, to our consolidated financial statements included in our 2025 Form 10-K. With respect to some loss contingencies, an estimate of the possible loss or range of loss cannot be made until management has further information, including, for example, (i) which claims, if any, will survive dispositive motion practice; (ii) information to be obtained through discovery; (iii) information as to the parties' damages claims and supporting evidence; (iv) the parties legal theories; and (v) the parties' settlement positions. If an estimate of the possible loss or range of loss can be made at this time, it is included in the potential loss contingency description below. The claims and legal proceedings in which we are involved also include challenges to the scope, validity or enforceability of the patents relating to our products, pipeline or processes and challenges to the scope, validity or enforceability of the patents held by others. These include claims by third parties that we infringe their patents. An adverse outcome in any of these proceedings could result in one or more of the following and have a material impact on our business or consolidated r …

LegalMattersAndContingenciesTextBlock · excerpt; the full note is in the filing

New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that we adopt as of the specified effective date. Unless otherwise discussed below, we do not believe that the adoption of recently issued standards have had, or may have, a material impact on our condensed consolidated financial statements or disclosures. Standard Description Effective Date Effects on the financial statements ASU No. 2024-03, Income Statement (Subtopic 220-40): Reporting Comprehensive Income - Expense Disaggregation Disclosures This standard requires disclosure in the notes to the financial statements, at each interim and annual reporting period, of specified information about certain costs and expense including purchases of inventory, employee compensation, depreciation and intangible asset amortization included in each relevant expense caption. This standard also requires a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated, as well as disclosure of the total amount of selling expenses, and, in annual reporting periods, an entitys definition of selling expenses. Annual reporting for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. We are currently evaluating the potential impact that this new standard will have on our consolidated financial statements and rel …

NewAccountingPronouncementsPolicyPolicyTextBlock · excerpt; the full note is in the filing

Note 4: Restructuring Apellis Integration Following the closing of the Apellis acquisition, we implemented an integration plan designed to realize operating synergies through cost savings and avoidance. For the three and six months ended June 30, 2026, we recognized approximately $153.2 million of net pre-tax restructuring charges, primarily consisting of employee severance costs and the acceleration of bonus payments that were subject to a double-trigger provision. Restructuring Reserve 2023 Fit for Growth Restructuring Program In 2023 we initiated cost saving measures as part of our Fit for Growth program to reduce operating costs, while improving operating efficiency and effectiveness. The Fit for Growth program generated approximately $1.0 billion in gross operating expense savings by the end of 2025, some of which has been reinvested in various initiatives. The Fit for Growth program included net headcount reductions of approximately 1,400 employees and we incurred total restructuring charges of approximately $320.0 million by the end of 2025. For the six months ended June 30, 2025, we recorded approximately $34.2 million in restructuring charges related to severance costs from our Fit for Growth program within restructuring charges in our condensed consolidated statements of income. Restructuring Reserve Charges and spending related to workforce reductions are summarized as follows: Workforce Reductions (In millions) 2026 2025 Restructuring reserve as of January 1 $ 15. …

RestructuringAndRelatedActivitiesDisclosureTextBlock · excerpt; the full note is in the filing

Note 5: Revenue Product Revenue Revenue by product is summarized as follows: For the Three Months Ended June 30, 2026 2025 (In millions) United States Rest of World Total United States Rest of World Total Multiple Sclerosis: TECFIDERA $ 32.4 $ 58.5 $ 90.9 $ 47.2 $ 146.4 $ 193.6 VUMERITY 172.0 24.5 196.5 188.0 24.3 212.3 Total Fumarate 204.4 83.0 287.4 235.2 170.7 405.9 AVONEX 120.9 49.1 170.0 121.7 56.0 177.7 PLEGRIDY 25.2 29.9 55.1 28.3 40.7 69.0 Total Interferon 146.1 79.0 225.1 150.0 96.7 246.7 TYSABRI 270.5 180.3 450.8 272.2 182.4 454.6 Subtotal: Multiple Sclerosis 621.0 342.3 963.3 657.4 449.8 1,107.2 Rare Disease: SPINRAZA 204.3 197.6 401.9 149.3 243.4 392.7 SKYCLARYS 82.3 85.6 167.9 78.0 52.3 130.3 QALSODY 8.3 23.6 31.9 7.5 12.5 20.0 Subtotal: Rare Disease 294.9 306.8 601.7 234.8 308.2 543.0 Specialized Immunology: SYFOVRE (1) 97.4 97.4 EMPAVELI (1) 30.4 30.4 Subtotal: Specialized Immunology 127.8 127.8 Biosimilars: BENEPALI 106.8 106.8 112.1 112.1 IMRALDI 37.8 37.8 46.7 46.7 FLIXABI 8.1 8.1 14.3 14.3 BYOOVIZ (2) 0.1 0.1 2.5 6.1 8.6 Subtotal: Biosimilars 0.1 152.7 152.8 2.5 179.2 181.7 Other: ZURZUVAE 70.7 0.1 70.8 46.4 46.4 Other (3) 0.4 0.4 Subtotal: Other 70.7 0.1 70.8 46.4 0.4 46.8 Total product revenue, net $ 1,114.5 $ 801.9 $ 1,916.4 $ 941.1 $ 937.6 $ 1,878.7 (1) EMPAVELI and SYFOVRE were obtained as part of our acquisition of Apellis in May 2026. (2) In the fourth quarter of 2025 we completed the sale of our rights to BYOOVIZ. (3) Other includes FUMADERM. For th …

RevenueFromContractWithCustomerTextBlock · excerpt; the full note is in the filing

Note 21: Segment Information We operate and are managed as one operating segment, and derive revenue from activities related to the discovery, development and delivery of innovative therapies for people living with serious and complex diseases. Our research and development organization is responsible for the research and discovery of new product candidates and supports development and registration efforts for potential future products. Our pharmaceutical, operations and technology organization manages the development of the manufacturing processes, clinical trial supply, commercial product supply, distribution, buildings and facilities. Our commercial organization is responsible for U.S. and international development of our commercial products. We are also supported by corporate staff functions. Our CEO, as the CODM, manages and allocates resources to the operations of our company on a total company basis by assessing the overall level of resources available and deciding how to best deploy these resources across functions, therapeutic areas and research and development projects that are in line with our long-term company-wide strategic goals. In making these decisions, our CEO is provided with and uses consolidated financial information for purposes of evaluating performance, forecasting future period financial results, allocating resources and setting incentive targets. The CODM performs this assessment based on the segments net income. Through this analysis, which includes …

SegmentReportingDisclosureTextBlock · excerpt; the full note is in the filing

"Note 1: Summary of Significant Accounting Policies References in these notes to ""Biogen,"" the ""company,"" ""we,"" ""us"" and ""our"" refer to Biogen Inc. and its consolidated subsidiaries. Business Overview Biogen is a global biopharmaceutical company focused on discovering, developing and delivering innovative therapies for people living with serious and complex diseases. We are focused on advancing our pipeline, including significant late stage programs, in neurology, specialized immunology and rare diseases across multiple modalities. Our drug discovery and development efforts are supported by internal research and development programs, external collaborations and acquisitions of businesses and assets. Our marketed products include VUMERITY, TYSABRI, TECFIDERA, AVONEX and PLEGRIDY for the treatment of MS; SPINRAZA for the treatment of SMA; SKYCLARYS for the treatment of FA; QALSODY for the treatment of ALS; SYFOVRE for the treatment of GA; and EMPAVELI for the treatment of PNH, C3G and primary IC-MPGN. We also have collaborations with Eisai on the commercialization of LEQEMBI for the treatment of Alzheimer's disease and Supernus on the commercialization of ZURZUVAE for the treatment of PPD. We have certain business and financial rights with current and other potential anti-CD20 therapies, pursuant to our collaboration arrangements with Genentech, a wholly owned member of the Roche Group. Under the collaboration arrangements, we currently recognize revenue from the foll …

SignificantAccountingPoliciesTextBlock · excerpt; the full note is in the filing

Note 13: Equity Accumulated Other Comprehensive Income (Loss) The following tables summarize the changes in AOCI, net of tax by component: For the Three Months Ended June 30, 2026 (In millions) Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax Currency Translation Adjustments, Net of Tax Total Balance, March 31, 2026 $ (1.6) $ (6.3) $ (9.9) $ (122.4) $ (140.2) Other comprehensive income (loss) before reclassifications 0.6 6.6 (0.3) (3.6) 3.3 Amounts reclassified from AOCI 1.0 8.2 9.2 Net current period other comprehensive income (loss) 1.6 14.8 (0.3) (3.6) 12.5 Balance, June 30, 2026 $ $ 8.5 $ (10.2) $ (126.0) $ (127.7) For the Six Months Ended June 30, 2026 (In millions) Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax Currency Translation Adjustments, Net of Tax Total Balance, December 31, 2025 $ 0.2 $ (58.9) $ (9.4) $ (113.9) $ (182.0) Other comprehensive income (loss) before reclassifications (1.2) 38.5 (0.8) (12.1) 24.4 Amounts reclassified from AOCI 1.0 28.9 29.9 Net current period other comprehensive income (loss) (0.2) 67.4 (0.8) (12.1) 54.3 Balance, June 30, 2026 $ $ 8.5 $ (10.2) $ (126.0) $ (127.7) For the Three Months Ended June 30, 2025 (In millions) Unrealized Gains (Losses …

StockholdersEquityNoteDisclosureTextBlock · excerpt; the full note is in the filing