Biogen's Q2 2025 Financial Overview

Biogen's Q2 2025 Financial Overview

• 1. SECOND QUARTER 2025 FINANCIAL RESULTS AND BUSINESS UPDATE July 31, 2025

• 2. This presentation and the discussions during this conference call contains forward-looking statements, relating to: our strategy and plans; potential of, and expectations for, our commercial business and pipeline programs; capital allocation and investment strategy; clinical development programs, clinical trials, and data readouts and presentations; regulatory discussions, submissions, filings, and approvals; the potential benefits, safety, and efficacy of our and our collaboration partners’ products and investigational therapies; the anticipated benefits and potential of investments, optimization of the cost structure including our "Fit for Growth" program, actions to improve risk profile and productivity of R&D pipeline, collaborations, and business development activities; our future financial and operating results; and our 2025 financial guidance. These forward-looking statements may be accompanied by such words as “aim,” “anticipate,” “assume,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “forecast,” “goal,” “guidance,” “hope,” “intend,” “may,” “objective,” “outlook,” “plan,” “possible,” “potential,” “predict,” “project,” “prospect,” “should,” “target,” “will,” “would,” and other words and terms of similar meaning. Drug development and commercialization involve a high degree of risk, and only a small number of research and development programs result in commercialization of a product. Results in early-stage clinical trials may not be indicative of full results or results from later stage or larger scale clinical trials and do not ensure regulatory approval. You should not place undue reliance on these statements. Given their forward-looking nature, these statements involve substantial risks and uncertainties that may be based on inaccurate assumptions and could cause actual results to differ materially from those reflected in such statements. This presentation and the discussions during this conference call include, among others, forward-looking statements including: our strategy to transform our product portfolio; expectations around the continued growth of our products; the potential to expand and advance our late-stage product pipeline; the goal of creating sustainable growth and long-term value for shareholders; and all statements and information relating to our full year 2025 financial guidance. These forward-looking statements are based on management's current beliefs and assumptions and on information currently available to management. Given their nature, we cannot assure that any outcome expressed in these forwardlooking statements will be realized in whole or in part. We caution that these statements are subject to risks and uncertainties, many of which are outside of our control and could cause future events or results to be materially different from those stated or implied in this document, including, among others, factors relating to: our substantial dependence on revenue from our products and other payments under licensing, collaboration, acquisition or divestiture agreements; uncertainty of long-term success in developing, licensing, or acquiring other product candidates or additional indications for existing products; expectations, plans, prospects and timing of actions relating to product approvals, approvals of additional indications for our existing products, sales, pricing, growth, reimbursement and launch of our marketed and pipeline products; the potential impact of increased product competition in the biopharmaceutical and healthcare industry, as well as any other markets in which we compete, including increased competition from new originator therapies, generics, prodrugs and biosimilars of existing products and products approved under abbreviated regulatory pathways; our ability to effectively implement our corporate strategy; the successful execution of our strategic and growth initiatives, including acquisitions; the drivers for growing our business; difficulties in obtaining and maintaining adequate coverage, pricing, and reimbursement for our products; the drivers for growing our business, including our dependence on collaborators and other third parties for the development, regulatory approval, and commercialization of products and other aspects of our business, which are outside of our full control; risks associated with current and potential future healthcare reforms; risks related to commercialization of biosimilars, which is subject to such risks related to our reliance on third-parties, intellectual property, competitive and market challenges and regulatory compliance; failure to obtain, protect, and enforce our data, intellectual property, and other proprietary rights and the risks and uncertainties relating to intellectual property claims and challenges; the risk that positive results in a clinical trial may not be replicated in subsequent or confirmatory trials or success in early stage clinical trials may not be predictive of results in later stage or large scale clinical trials or trials in other potential indications; risks associated with clinical trials, including our ability to adequately manage clinical activities, unexpected concerns that may arise from additional data or analysis obtained during clinical trials, regulatory authorities may require additional information or further studies, or may fail to approve or may delay approval of our drug candidates; the occurrence of adverse safety events, restrictions on use with our products, or product liability claims; risks relating to technology, including our incorporation of new technologies such as artificial intelligence into some of our processes; risks related to use of information technology systems and potential impacts of any breakdowns, interruptions, invasions, corruptions, data breaches, destructions and/or other cybersecurity incidents of our systems or those of connected and/or third-party systems; problems with our manufacturing capacity, including our ability to manufacture products efficiently or adequately address global bulk supply risks; risks relating to management, personnel and other organizational changes, including our ability to attracting, retaining and motivating qualified individuals; risks related to the failure to comply with current and new legal and regulatory requirements, including judicial decisions, accounting standards, and tariff or trade restrictions; the risks of doing business internationally, including geopolitical tensions, acts of war and large-scale crises; risks relating to investment in our manufacturing capacity; risks relating to the distribution and sale by third parties of counterfeit or unfit versions of our products; risks relating to the use of social media for our business, results of operations and financial condition; fluctuations in our operating results; risks related to investment in properties; risks relating to access to capital and credit markets to finance our present and future operations and business initiatives and obtain funding for such activities on favorable terms; risks related to indebtedness; the market, interest, and credit risks associated with our investment portfolio; risks relating to share repurchase programs; change in control provisions in certain of our collaboration agreements; fluctuations in our effective tax rate and obligations in various jurisdictions in which we are subject to taxation; environmental risks; and any other risks and uncertainties that are described in other reports we have filed with the U.S. Securities and Exchange Commission. These statements speak only as of the date of this presentation and the discussions during this conference call and are based on information and estimates available to us at this time. Should known or unknown risks or uncertainties materialize or should underlying assumptions prove inaccurate, actual results could vary materially from past results and those anticipated, estimated or projected. Investors are cautioned not to put undue reliance on forward-looking statements. A further list and description of risks, uncertainties and other matters can be found in our Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and in our subsequent reports on Form 10-Q and Form 10- K, in each case including in the sections thereof captioned “Note Regarding Forward-Looking Statements” and “Item 1A. Risk Factors,” and in our subsequent reports on Form 8-K. Except as required by law, we do not undertake any obligation to publicly update any forward-looking statements whether as a result of any new information, future events, changed circumstances or otherwise. FORWARD-LOOKING STATEMENTS 2

• 3. This presentation and the discussions during this conference call include certain financial measures that were not prepared in accordance with accounting principles generally accepted in the U.S. (GAAP), including adjusted net income, adjusted diluted earnings per share, revenue growth at constant currency, which excludes the impact of changes in foreign exchange rates and hedging gains or losses, and free cash flow, which is defined as net cash flow from operations less capital expenditures. Additional information regarding the GAAP and Non-GAAP financial measures and a reconciliation of the GAAP to Non-GAAP financial measures can be found in the appendix of this presentation and in the Q2 2025 earnings release and related financial tables posted on the Investors section of Biogen.com. We believe that these and other Non-GAAP financial measures provide additional insight into the ongoing economics of our business and reflect how we manage our business internally, set operational goals, and form the basis of our management incentive programs. Non-GAAP financial measures are in addition to, not a substitute for, or superior to, measures of financial performance prepared in accordance with GAAP. We do not provide guidance for GAAP reported financial measures (other than revenue) or a reconciliation of forward-looking Non-GAAP financial measures to the most directly comparable GAAP reported financial measures because we are unable to predict with reasonable certainty the financial impact of items such as the transaction, integration, and other costs related to acquisitions or business development transactions; unusual gains and losses; potential future asset impairments; gains and losses from our equity security investments; the ultimate outcome of litigation and other non-recurring items. These items are uncertain, depend on various factors, and could have a material impact on GAAP reported results for the guidance period. For the same reasons, we are unable to address the significance of the unavailable information, which could be material to future results. Note regarding trademarks: ADUHELM®, AVONEX®, BYOOVIZ®, PLEGRIDY®, QALSODY®, RITUXAN®, RITUXAN HYCELA®, SKYCLARYS®, SPINRAZA®, TECFIDERA®, TYSABRI®, and VUMERITY® are registered trademarks of Biogen. BENEPALI , FLIXABI , FUMADERM , IMRALDI , and OPUVIZ are trademarks of Biogen. The following are trademarks of the respective companies listed: LEQEMBI® – Eisai Co., Ltd.; ZURZUVAE – Sage Therapeutics Inc.; COLUMVI®, GAZYVA®, LUNSUMIO®, OCREVUS® – Genentech, Inc. Other trademarks referenced in this presentation are the property of their respective owners. NON-GAAP FINANCIAL INFORMATION 3

• 4. BIOGEN CALL PARTICIPANTS 4 Christopher A. Viehbacher President and Chief Executive Officer Robin Kramer Chief Financial Officer Priya Singhal, M.D., M.P.H. Head of Development Alisha A. Alaimo President and Head of North America

• 5. KEY HIGHLIGHTS President and Chief Executive Officer Christopher A. Viehbacher

• 6. DURING Q2 WE CONTINUED TO DELIVER AGAINST OUR STRATEGY FOR LONG-TERM GROWTH Note: LEQEMBI (lecanemab-irmb) is being developed in collaboration with Eisai Co., Ltd; ZURZUVAE is being developed in collaboration with Sage Therapeutics, Inc.; CHMP = Committee for Medicinal Products for Human Use; FA = Friedreich ataxia; IgAN = IgA nephropathy; PMN = primary membranous nephropathy; SLE = systemic lupus erythematosus; SMA = spinal muscular atrophy. 1. Includes markets with either a commercial launch or access through a paid or free early access mechanism as of July 30, 2025. • Continued strength from new launches with revenue offsetting MS decline • LEQEMBI showed sustained sequential growth with rising global demand • SKYCLARYS now available in 29 markets1 globally and Phase 3 pediatric study underway • ZURZUVAE revenue grew 68% sequentially driven by increased demand; Received positive CHMP opinion in the E.U. • Strategic research agreement with City Therapeutics aiming to develop novel RNAi-based therapies • Continued investment to support the pipeline and expand capabilities Commercial Performance • Phase 3 studies initiated for felzartamab in IgAN and PMN and SKCLARYS in pediatric FA • Positive Phase 1b results for salanersen supporting moving to registrational status and our potential long-term leadership in SMA • New analyses of dapirolizumab pegol Phase 3 data in SLE show improvement in fatigue and reduction in disease activity 6 Pipeline Advancement BD and Capital Allocation

• 7. STRONG EXECUTION ACROSS AN EXPANDING PIPELINE INCLUDING MORE LATE-STAGE OPPORTUNITIES *Collaboration program; ^ Licensed from Ionis Pharmaceuticals, Inc. AD = Alzheimer’s disease; AMR = antibody mediated rejection; ASO = antisense oligonucleotide; CLE = cutaneous lupus erythematosus; IgAN = IgA nephropathy; LN = lupus nephritis; LRRK2 = leucine rich repeat kinase 2; MS = multiple sclerosis; MVI = microvascular inflammation in kidney transplant patients; PMN = primary membranous nephropathy; SLE = systemic lupus erythematosus; SMA = spinal muscular atrophy 7 Alzheimer’s disease Lecanemab (Aβ mAb)* – Preclinical AD BIIB080 (tau ASO)^ – Early AD Immunology Dapirolizumab pegol (anti-CD40L)* – SLE Litifilimab (anti-BDCA2 mAb) – SLE Litifilimab (anti-BDCA2 mAb) – CLE Felzartamab (anti-CD38 mAb) – LN Potential new IND with Phase 1 study planned Nephrology Felzartamab (anti-CD38 mAb) – Late AMR Felzartamab (anti-CD38 mAb) – IgAN Felzartamab (anti-CD38 mAb) – PMN Felzartamab (anti-CD38 mAb) – Late MVI Neuromuscular SKYCLARYS (Nrf2 activator) – Pediatric FA Salanersen (SMN ASO)^ – SMA Neurodevelopmental Zorevunersen (SCN1A ASO)* - Dravet syndrome Parkinson’s disease BIIB122 (LRRK2 inhibitor)* – Parkinson’s Multiple Sclerosis BIIB091 (peripheral BTK Inhibitor) – MS Phase 1 Phase 2 Phase 3 Phase 3 study now underway Phase 3 study now underway Phase 3 initiation planned by early 2026 Phase 3 study initiation planned in 2025 Randomized Phase 2 study planned New Asset New Program New Phase 3 Asset Phase 3 study now underway

• 8. DEVELOPMENT UPDATE Head of Development Priya Singhal, M.D., M.P.H.

• 9. FURTHER STRENGTHENED OUR PIPELINE IN Q2 TO SUPPORT OUR LONG-TERM GROWTH OBJECTIVE Phase 1 Phase 2 Phase 3 Regulatory Review in Certain Markets Felzartamab (anti-CD38 mAb) – LN BIIB080 (tau ASO)^ Early AD Lecanemab (Aβ mAb)* SC-AI Initiation Early AD Felzartamab (anti-CD38 mAb) Late AMR Lecanemab (Aβ mAb)* SCAI Maintenance Early AD BIIB122 (LRRK2 inhibitor)* – PD Lecanemab (Aβ mAb)* Preclinical AD Felzartamab (anti-CD38 mAb) – IgAN HD Nusinersen (SMN2 splice modulator) SMA BIIB091 (peripheral BTK Inhibitor) – MS Dapirolizumab pegol (anti-CD40L)* – SLE Felzartamab (anti-CD38 mAb) – PMN ZURZUVAE (GABAA PAM)* – PPD Review in Europe Felzartamab (anti-CD38 mAb) Late MVI Phase 2 planned Litifilimab (BDCA2 mAb) – SLE SKYCLARYS (Nrf2 activator) – Pediatric FA Litifilimab (BDCA2 mAb) – CLE Zorevunersen (SCN1A ASO)* – Dravet syndrome Phase 3 planned in 2025 Salanersen (BIIB115) (SMN ASO)^ – SMA Phase 3 planned by early 2026 AD and Dementia Immunology Neuropsych Parkinson’s disease MS Neuromuscular disorders Pipeline Updates: Added = Felzartamab Phase 2 planned in MVI; Advanced = Felzartamab programs in PMN and IgAN to Phase 3, SKYCLARYS in pediatric FA to Phase 3, Salanersen moved to registrational status; Discontinued = Izastobart in complement mediated disease. *Collaboration program; ^ Licensed from Ionis Pharmaceuticals, Inc.; AAIC = Alzheimer’s Association International Conference; AD = Alzheimer’s disease; AMR = antibody mediated rejection; ASO = antisense oligonucleotide; CLE = cutaneous lupus erythematosus; FA = Friedreich ataxia; EULAR = European Alliance of Associations for Rheumatology; EPNS = European Paediatric Neurology Society; GABA = γ-Aminobutyric acid; HD = higher dose; IgAN = IgA nephropathy; LN = lupus nephritis; LRRK2 = leucine rich repeat kinase 2; MS = multiple sclerosis; MVI = microvascular inflammation in kidney transplant patients; PAM = positive allosteric modulator; PD = Parkinson’s disease; PMN = primary membranous nephropathy; PPD = postpartum depression; SC-AI = subcutaneous autoinjector; SLE = systemic lupus erythematosus; SMA = spinal muscular atrophy; SMN = survival motor neuron Neurodevelopmental 9 Development Milestones: Continued scientific leadership with new data presentations at AAIC, EPNS, Cure SMA, EULAR and Lupus 2025 Nephrology • ZURZUVAE: Positive CHMP opinion in the E.U. • SKYCLARYS: Initiated Phase 3 study in pediatric FA • Felzartamab: Phase 3 studies underway with new Phase 2 study planned in MVI • Salanersen: Positive Phase 1b interim results

• 10. WE RAN A PHASE 1B STUDY TO EVALUATE ONCE YEARLY SALANERSEN IN SMA PATIENTS WHO PREVIOUSLY RECEIVED GENE THERAPY Source: Sansone et al., Annual Cure SMA Research and Clinical Care Meeting, 2025 1. Schedule shown reflects in-person visits. Not shown: 2 telephone visits per year. AE = adverse event; ASO = anti-sense oligonucleotide; CHOP-INTEND: Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders; CSF = cerebrospinal fluid’ IV = intravenous; HFMSE = Hammersmith Functional Motor Scale – Expanded; HINE = Hammersmith Infant Neurological Examination; IT = intrathecal; OA = Onasemnogene abeparvovec; RULM = revised upper limb module; SAE = serious adverse event; SMA = spinal muscular atrophy; WHO = world health organization Primary Endpoint • Safety (incidence of AEs / SAEs) Key Secondary Endpoint • Pharmacokinetics (serum and CSF) Key Exploratory Endpoints • Neurofilaments • WHO motor milestones • Motor function assessments • Older: HFMSE, RULM • Younger: HINE-2, CHOP-INTEND Participants must have suboptimal clinical status in > 1 of 4 domains as determined by study investigator at screening: • Motor function • Respiratory function • Swallowing or feeding ability for age • Other Salanersen is a novel ASO leveraging the same mechanism of action of SPINRAZA but designed for high potency to address the remaining unmet need in SMA Intracohort dose staggering: safety review of older subgroup (aged 2-12 yrs) prior to dosing younger subgroup (aged 0.5 to <2 yrs) IT salanersen: • 40 mg dose, n = 12 • 80 mg dose, n = 12 SMA diagnosis IV OA Screening (Days --28 to –1) ≥ 6 mo before Study Day 1 Salanersen Dose Study Day1 1 8 30 90 180 270 360 368 390 450 540 630 720 10

• 11. 11 INTERIM PHASE 1B RESULTS SUPPORT ADVANCEMENT TO PHASE 3 AND HIGHLIGHT SALANERSEN’S POTENTIAL TO TRANSFORM SMA CARE Next Steps: Phase 3 study expected to start by early 2026 Case study examples* Study Day: 1 90 180 • Clinically meaningful improvements in motor function from baseline to 1-year on the HFMSE and the RULM scales (n=8)1 • 70% reduction in NfL at 6 months and sustained through 1-year (n =24)2 • Cumulative Phase 1 data indicate that salanersen has a generally well tolerated safety profile Interim Phase 1b results Source: Sansone et al., Annual Cure SMA Research and Clinical Care Meeting, 2025 1. Interim analysis at a time point where all of the older, 2-12 year old participants in the lower dose cohort had the opportunity for at least 1 year of follow-up. Clinical outcome results are only presented for this cohort; 2. In participants with elevated NfL levels at baseline. Elevated baseline defined as exceeding 95th percentile for serum in neurologically healthy children of similar ages. * Each patient experience is unique and not representative of the patient population as a whole. These patient’s experience is not intended to depict what other patients may experience. SMN = survival motor neuron Data shows that salanersen resulted in substantial slowing of neurodegeneration and clinically meaningful improvements in children previously treated with gene therapy Patient #2: 5 years old with 3 SMN2 copies; received gene therapy >3 years prior to 40 mg salanersen initiation Unable to walk alone Walking alone Walking alone 360 Patient #1: 5 years old with 2 SMN2 copies; received gene therapy ~4 years prior to 80 mg salanersen initiation Unable to sit without support Sitting without support Sitting without support

• 12. Note: Dapirolizumab pegol is being developed in collaboration with UCB; 1. Touma et al., Lupus, 2025; 2. Parodis et al., EULAR, 2025; 3.Morand et al., EULAR, 2025; *Nominal p<0.05 DZP = dapirolizumab pegol; FACIT = Functional Assessment of Chronic Illness Therapy; HRQoL = health-related quality of life; SoC = standard of care 12 NEW DATA HIGHLIGHTS THE POTENTIAL OF DAPIROLIZUMAB PEGOL TO ALLEVIATE FATIGUE, REDUCE DISEASE ACTIVITY AND IMPROVE QUALITY OF LIFE IN LUPUS Dapirolizumab pegol showed efficacy across multiple clinical endpoints in the positive PHOENYCS GO Phase 3 study, including fatigue, measures of disease activity and patient reported outcomes • Improvements from baseline to week 48 in LupusQoL scores across all domains1 • Improvements across multiple domains of fatigue measured by both FACIT and FATIGUE-PRO2 • Measures of disease activity and remission, improved over time through 48 weeks of treatment3 New PHOENYCS GO data show that compared to SoC alone, DZP + SoC resulted in: Worse HRQoL Better HRQoL 0 100 PBO+SOC (n=107) DZP+SOC (n=208) Second confirmatory PHOENYCS FLY Phase 3 study ongoing Change in LupusQoL scores from baseline to Week 48

• 13. OUR DISCIPLINED SCIENTIFIC APPROACH IS POISED TO DELIVER KEY EXPECTED MILESTONES OVER THE NEXT 18 MONTHS LEQEMBI (lecanemab-irmb) is being developed in collaboration with Eisai Co; BIIB080 is licensed from Ionis Pharmaceuticals, Inc.; Zorevunersen is being developed in collaboration with Stoke therapeutics; *Stoke has disclosed that first sites have initiated in the U.S. in May 2025; # Readout expected H2 2026 to H1 2027. AD = Alzheimer’s disease; AI = autoinjector; CHMP = Committee for Medicinal Products for Human Use; CLE = cutaneous lupus erythematosus; DS = Dravet syndrome; FA = Friedreich’s ataxia; IgAN = IgA nephropathy; IND = investigational new drug application; LN = lupus nephritis; MVI = microvascular inflammation; PD = Parkinson’s disease; PPD = postpartum depression; PMN = primary membranous nephropathy; SC = subcutaneous; SLE = systemic lupus erythematosus; SMA = spinal muscular atrophy Study Starts Clinical Trial Readouts Regulatory Decisions • Felzartamab Phase 3 in IgAN • Felzartamab Phase 3 in PMN • SKYCLARYS Phase 3 in pediatric FA • Zorevunersen Phase 3 in DS* • Salanersen Phase 3 in SMA • Felzartamab randomized Phase 2 in Late MVI • Potential new IND in immunology • Salanersen Phase 1b interim in SMA • Litifilimab Phase 3 in SLE • Litifilimab Phase 3 in CLE# • BIIB080 Phase 2 in Early AD • Felzartamab Phase 1 in LN • Zuranolone in PPD • LEQEMBI SC-AI maintenance in Early AD • LEQEMBI SC-AI initiation in Early AD • Nusinersen (SPINRAZA) higher dose in SMA 4 4 3 13 New First Phase 3 by end of 2026 Late 2026 to early 2027 By mid-year 2026 2026 Positive CHMP opinion FDA PDUFA: August 31, 2025 Expected regulatory decision in H1 2026 FDA PDUFA: September 22, 2025 Biogen will host our next thematic seminar on September 3rd and will focus on our lupus pipeline

• 14. COMMERCIAL UPDATE President and Head of North America Alisha A. Alaimo

• 15. EXPANDING SKYCLARYS GLOBALLY TO REALIZE FULL POTENTIAL • Now available in 291 countries with Q2 worldwide sales of $130 million, up 30% YoY and 5% QoQ • U.S. seeing impact of focused investments on reaching community HCPs and slower progressing patients o ~70% of Q2 new U.S. patient starts from community prescribers o U.S. sales of $78 million, up 3% YoY and 13% QoQ • SKYCLARYS is now included in treatment guidelines For Friedreich Ataxia See SKYCLARYS USPI for full prescriber information FA stands for Friedreich Ataxia; HCPs stands for health care professionals Actual paid patient 1. Includes markets with either a commercial launch or access through a paid or free early access mechanism as of July 30, 2025. 15

• 16. ZURZUVAE RAPIDLY GROWING AS A FIRST LINE THERAPY FOR PPD • Q2 U.S. sales of $46 million, up 213% YoY and 68% QoQ • Field expansion driving performance across key metrics in Q2 o 29% increase in prescribers in Q2 o 70% of prescriptions from repeat prescribers o 80% of prescriptions are for first line therapy1 See ZUZRUVAE USPI for full prescriber information PPD stands for Postpartum Depression Actual paid patient 16 For Postpartum Depression 1. Based on second quarter claims data through end of May.

• 17. UNLOCKING NEW INVESTMENTS TO DRIVE LEQEMBI GROWTH WITH IMPORTANT OPPORTUNITIES AHEAD • Q2 worldwide sales of $160 million shows continued growth excluding the $35 million stocking in China; U.S. sales of $63M increased 20% QoQ • U.S. prescriber base grew 34% in first half of 2025; increased number of repeat prescribers • Anti-amyloid therapy market growth estimated ~15% in Q21 • Monthly PET increased 5x and blood-based biomarker testing nearly tripled in the last year2 • DTC campaign and primary care pilot to support patient awareness and engagement See LEQEMBI USPI for full prescriber information Actual paid patient 1. Data from new patient starts 2. Data from two of the major lab companies 17 For Early Alzheimer's Disease

• 18. FINANCIAL UPDATE Chief Financial Officer Robin Kramer

• 19. SECOND QUARTER 2025 KEY FINANCIAL HIGHLIGHTS Total Revenue 19 Full Year 2025 Guidance Raised $2.65B 7% YoY GAAP Diluted EPS Non-GAAP Diluted EPS Cash and Cashflow $4.33 8% YoY $5.47 4% YoY • $252M 26% QoQ and 91% YoY • YoY increase in launch revenue offset YoY decline in MS product revenue • Generated $134M of free cash flow - includes impact from $745M of Q2 2025 tax payments • $2.8B of cash and $3.5B of net debt as of June 30, 2025 Our GAAP financial measures and a reconciliation of GAAP to Non-GAAP financial results are at the end of this presentation. * Launch products = SKYCLARYS, QALSODY, and ZURZUVAE, plus Biogen’s 50% share of net revenue and cost of sales, including royalties, from the LEQEMBI Collaboration free cash flow = net cash flow from operations less capital expenditures – see slide 22 for details; FY = full year; IPR&D = in-process research and development; Q2 = second quarter; YoY = year-over-year • Expect FY 2025 Non-GAAP diluted EPS between $15.50 and $16.00, up from between $14.50 and $15.50 previously • Expect FY 2025 total revenue to be approximately flat, at constant currency, versus FY 2024, up from a mid-single digit decline previously GAAP Operating Income • 1% YoY ( 6% YoY excluding impact from acquired IPR&D charges) Launch Products* Performance Non-GAAP Operating Income • 1% YoY ( 5% YoY excluding impact from acquired IPR&D charges)

• 20. SECOND QUARTER 2025 REVENUE HIGHLIGHTS CC = Constant Currency – Percentage changes in revenue growth at constant currency are presented excluding the impact of changes in foreign currency exchange rates and hedging gains or losses. Foreign currency revenue values are converted into U.S. Dollars using the exchange rates from the end of the previous calendar year. NMF = no meaningful figure; YoY = year-over-year Note: Numbers may not foot due to rounding. Percent changes represented as favorable/(unfavorable). 1 includes TECFIDERA, VUMERITY, AVONEX, PLEGRIDY, TYSABRI, and FAMPYRA. Effective January 1, 2025, our collaboration and license agreement for FAMPYRA global commercialization rights was terminated. 2 includes SPINRAZA, SKYCLARYS, and QALSODY. 3 includes ADUHELM, FUMADERM and ZURZUVAE. 4 includes Biogen’s 50% share of net revenue and cost of sales, including royalties, from the LEQEMBI Collaboration. ($ in Millions) Q2 2025 Q2 2024  YoY  CC* Multiple sclerosis product revenue1 $1,107 $1,150 (4%) (4%) Total rare disease revenue2 $543 $534 2% 3% Biosimilars revenue $182 $198 (8%) (8%) Other product revenue3 $47 $18 169% 170% Revenue from anti-CD20 therapeutic programs $467 $445 5% 5% Alzheimer’s collaboration revenue4 $55 $12 NMF NMF Contract manufacturing, royalty and other revenue $245 $109 124% 119% Total revenue $2,646 $2,465 7% 8% 20

• 21. SECOND QUARTER 2025 KEY P&L ITEMS ($ in Millions except EPS, Shares in Millions) Q2 2025 Q2 2024 Δ Y/Y ($ in Millions except EPS, Shares in Millions) Q2 2025 Q2 2024 Δ Y/Y Total Revenue $2,646 $2,465 7% Total Revenue $2,646 $2,465 7% GAAP Cost of Sales* $605 $546 (11%) Non-GAAP Cost of Sales* $554 $504 (10%) % of revenue 23% 22% % of revenue 21% 20% GAAP R&D Expense $399 $505 21% Non-GAAP R&D Expense $394 $455 13% GAAP SG&A Expense $584 $554 (5%) Non-GAAP SG&A Expense $579 $542 (7%) GAAP Acquired IPR&D, Upfront and Milestone Expense $47 $9 NMF Non-GAAP Acquired IPR&D, Upfront and Milestone Expense $47 $9 NMF GAAP Operating Income $795 $784 1% Non-GAAP Operating Income $984 $971 1% GAAP Other (Income) Expense $49 $85 42% Non-GAAP Other (Income) Expense $57 $55 (4%) GAAP Taxes % 14.7% 16.5% Non-GAAP Taxes % 13.5% 15.9% GAAP Net Income Attributable to Biogen Inc. $635 $584 9% Non-GAAP Net Income Attributable to Biogen Inc. $803 $771 4% Weighted Average Diluted Shares 147 146 (1%) Weighted Average Diluted Shares 147 146 (1%) GAAP Diluted EPS $4.33 $4.00 8% Non-GAAP Diluted EPS $5.47 $5.28 4% Approx. impact from acquired IPR&D ($0.26) Approx. impact from acquired IPR&D ($0.26) * Excluding amortization and impairment of acquired intangible assets. The above table is not an income statement. Numbers do not foot. Percent changes represented as favorable/(unfavorable). Our GAAP financial measures and a reconciliation of GAAP to Non-GAAP financial results are at the end of this presentation. 21

• 22. EXPECTED CASH FLOW SUPPORTS A BALANCE SHEET THAT ALLOWS FOR INVESTMENT TO AUGMENT GROWTH Balance Sheet* Q2 2025 Cash Flow $2.8B Cash and cash equivalents $6.3B Debt $3.5B Net debt $161M Cash flow from operations $27M Capital expenditures $134M Free cash flow# Note: Numbers may not foot due to rounding. * As of June 30, 2025. # Free cash flow is defined as net cash flow from operations less capital expenditures. 22 Includes impact from $745M of tax payments

• 23. Significant U.S. Manufacturing Footprint OUR BUSINESS MODEL AND FOOTPRINT POSITIONS US FOR POTENTIAL RESILIENCE IN UNCERTAIN ENVIRONMENTS Strong Geographic Diversification ~75% of 2024 U.S. product revenue is attributable to products which are largely manufactured in the U.S. ~55% of 2024 product revenue attributable to sales outside the U.S. * Full year 2024 U.S. product revenue Product revenue includes TECFIDERA, VUMERITY, AVONEX, PLEGRIDY, TYSABRI, FAMPYRA, SPINRAZA, SKYCLARYS, QALSODY, ADUHELM, FUMADERM, ZURZUVAE, TOFIDENCE, BYOOVIZ, FLIXABI, BENEPALI, and IMRALDI Products largely manufactured in the U.S. = AVONEX, PLEGRIDY, SKYCLARYS, SPINRAZA, QALSODY, and TYSABRI Core pharmaceutical revenue = product revenue, excluding biosimilars revenue, plus Biogen’s 50% share of net revenue and cost of sales, including royalties, from the LEQEMBI Collaboration. 23 Diversified U.S. Payor Channel Mix ~60% commercial, ~40% government 75% 25% Products which are largely manufactured in the U.S. Revenue from Rare Disease ~31% of 2024 core pharmaceutical revenue attributable to rare disease products 45% 55% U.S. ROW 31% 69% Rare disease products 60% 40% Commercial channels Government channels U.S. Product Revenue Total Product Revenue Core Pharmaceutical Revenue U.S. Product Revenue*

• 24. UPDATED GUIDANCE REFLECTS AN EXPECTED STRONGER BUSINESS OUTLOOK FOR FULL YEAR 2025 Please see Biogen’s Q2 2025 earnings release, available at the Investors section of Biogen’s website at investors.biogen.com, for additional 2025 financial guidance assumptions. This financial guidance incorporates the Company's view that Biogen's 2025 financial outlook is not currently expected to be materially impacted by potential pharmaceutical tariffs as announced by the U.S. Administration on April 2, 2025, even if the exemption for pharmaceuticals were to be removed. This is based on both a significant proportion of U.S. revenue being derived from products which have manufacturing operations in the United States, and the Company's current global inventory positions. The U.S. and international tariff landscape remains uncertain, and this guidance does not include contemplation of any new tariffs. This financial guidance does not include any impact from potential acquisitions or business development transactions or pending and future litigation or any impact of potential tax or healthcare reform, as all are hard to predict. Biogen may incur charges, realize gains or losses, or experience other events or circumstances in 2025 that could cause any of these assumptions to change and/or actual results to vary from this financial guidance. Please see slide 3 of this presentation for additional information on our use of Non-GAAP measures, including forward-looking Non-GAAP financial measures. FY = full year Full Year 2025 Non-GAAP Diluted EPS Prior FY 2025 Guidance (May) $14.50 to $15.50 Benefit from stronger business outlook +$0.87 Approx. impact from City Therapeutics transaction ($0.12) Updated FY 2025 Guidance $15.50 to $16.00 24

• 25. UPDATED KEY CONSIDERATIONS FOR FULL YEAR 2025 FINANCIAL GUIDANCE Tariffs/Macro Total Revenue Fit for Growth • On track to deliver $1B/gross and $800M/net savings from Fit for Growth by the end of 2025 • FY 2025 not expected to be materially impacted by the potential tariffs as announced by the U.S. Administration on April 2, 2025, even if the exemption for pharmaceuticals were to be removed. Our guidance does not contemplate any new tariffs that may be announced in the future. • Increased expected full year 2025 total revenue to be approximately flat, at constant currency, versus FY 2024, up from a mid-single digit decline previously Contract Manufacturing Revenue P&L • Expect FY 2025 contract manufacturing revenue to be roughly consistent with FY 2024 • Expect minimal Q4 revenue due to planned plant maintenance • In 2025, we plan to make additional investments in R&D to enable acceleration and expansion of the clinical development pipeline, primarily in support of rare disease – Expect FY 2025 OpEx to be ~$4.0B • Expect FY 2025 OIE to be a net expense of $170-180M • Identified ~$15M of potential acquired IPR&D in 2H to-date • Expect FY 2025 gross margin percentage and operating margin percentage to remain relatively flat versus FY 2024 excluding acquired IPR&D Note: identified acquired IPR&D includes potential milestones and opt-in payments that could occur in the second half of 2025 FY = full year; GTN = gross-to-net; IPR&D = in-process research and development; MS = multiple sclerosis; OIE = Non-GAAP other income and expense; OpEx = Non-GAAP R&D expense and Non-GAAP SG&A expense 25 MS Revenue • Excluding favorability from inventory and one-time GTN adjustments of $75M, U.S. revenue trends for the second half of 2025 expected to be roughly in line with the first half • Expect increased pace of erosion on our ex-U.S. MS business in the second half of 2025, particularly for TECFIDERA in the E.U.

• 26. QUESTIONS & ANSWERS

• 27. APPENDIX

• 28. CONSOLIDATED STATEMENT OF INCOME (unaudited, in millions, except per share amounts) 28

• 29. CONSOLIDATED BALANCE SHEETS (unaudited, in millions) 29

• 30. PRODUCT REVENUE (U.S. AND REST OF WORLD) & TOTAL REVENUE (unaudited, in millions) 30

• 31. GAAP TO NON-GAAP RECONCILIATION (unaudited, in millions) Use of Non-GAAP Financial Measures We supplement our GAAP consolidated financial statements and GAAP financial measures with other financial measures, such as adjusted net income, adjusted diluted earnings per share, revenue change at constant currency, which excludes the impact of changes in foreign exchange rates and hedging gains or losses, and free cash flow, which is defined as net flow from operations less capital expenditures. We believe that these and other Non-GAAP financial measures provide additional insight into the ongoing economics of our business and reflect how we manage our business internally, set operational goals and form the basis of our management incentive programs. Non-GAAP financial measures are in addition to, not a substitute for, or superior to, measures of financial performance prepared in accordance with GAAP. Our “Non-GAAP net income attributable to Biogen Inc.” and “Non-GAAP earnings per share - Diluted” financial measures exclude the following items from “GAAP net income attributable to Biogen Inc.” and “GAAP earnings per share - Diluted”: 1. Acquisitions and divestitures We exclude transaction, integration and certain other costs related to the acquisition and divestiture of businesses/commercial assets and items associated with the initial consolidation or deconsolidation of variable interest entities. These adjustments include, but are not limited to, the amortization of inventory fair value step-up, amortization and impairment of intangible assets, charges or credits from the fair value remeasurement of our contingent consideration obligations and losses on assets and liabilities held for sale. 2. Restructuring, business transformation and other cost saving initiatives We exclude costs associated with our execution of certain strategies and initiatives to streamline operations, achieve targeted cost reductions, rationalize manufacturing facilities or refocus research and development activities. These costs may include employee separation costs, retention bonuses, facility closing/abandonment and exit costs, asset impairment charges or additional depreciation when the expected useful life of certain assets have been shortened due to changes in anticipated usage and other costs or credits that management believes do not have a direct correlation to our ongoing or future business operations. 3. (Gain) loss on equity security investments We exclude unrealized and realized gains and losses on our equity security investments as we do not believe that these components of income or expense have a direct correlation to our ongoing or future business operations. 4. Other items We evaluate other items of income and expense on an individual basis and consider both the quantitative and qualitative aspects of the item, including (i) its size and nature, (ii) whether or not it relates to our ongoing business operations and (iii) whether or not we expect it to occur as part of our normal business on a regular basis. We also include an adjustment to reflect the related tax effect of all reconciling items within our reconciliation of our GAAP to Non-GAAP net income attributable to Biogen Inc. and earnings per share - diluted. 31

• 32. GAAP TO NON-GAAP RECONCILIATION Continued (unaudited, in millions, except effective tax rates & per share amounts) 32

• 33. GAAP TO NON-GAAP RECONCILIATION Continued Revenue Change at Constant Currency vs Q2 2024 (unaudited) 33

• 34. GAAP TO NON-GAAP RECONCILIATION Continued Free Cash Flow (unaudited, in millions) 34

• 35. LEQEMBI COLLABORATION ACCOUNTING Biogen Revenue Product revenue, net Less cost of sales Less royalties Alzheimer's collaboration revenue • Eisai records 100% of net product revenue globally • Biogen’s 50% share of LEQEMBI revenue, net and cost of sales (including royalties) is recorded in “Alzheimer's collaboration revenue” • Biogen manufactures LEQEMBI drug substance • Biogen sells drug substance to Eisai and recognizes contract manufacturing revenue and contract manufacturing cost of sales Revenue (Manufacturing) Revenue (Commercial) Contract manufacturing revenue Less cost of sales Biogen Revenue Biogen Cost of Sales • Biogen’s 50% share of R&D and SG&A expenditures are reflected within Biogen’s R&D expense and SG&A expense, respectively Expenses 35

• 36. ZURZUVAE COLLABORATION ACCOUNTING Commercial Economics (U.S.) Biogen P&L 50% of operating profits (losses) to/from Sage recorded in Biogen’s collaboration profit sharing/(loss reimbursement) expense line ZURZUVAE net revenue (100%) Biogen cost of sales (100%) Biogen’s SG&A (100%) Collaboration profit sharing/(loss reimbursement) R&D Expense • Biogen’s 50% share of R&D expenditures are reflected within R&D expense • Outside of the U.S., Biogen is responsible for development and commercialization, excluding Japan, Taiwan and South Korea, and may pay Sage potential tiered royalties in the high-teens to low-twenties Ex-U.S. • Biogen reflects net revenue on sales of ZURZUVAE and records Biogen’s cost of sales and SG&A in their respective line items. Biogen shares 50% of the profit or loss with Sage, which is recognized in the “collaboration profit sharing/(loss reimbursement)” line on the P&L 36