BIIB Q1 26 Earnings Presentation Final

April 29, 2026

OTHER INFORMATION

Non-GAAP Financial Information

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 Q1 2026 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®, FUMADERM®, PLEGRIDY®, QALSODY®, RITUXAN®, RITUXAN HYCELA®, SKYCLARYS®, SPINRAZA®, TECFIDERA®, THECAFLEX DRX ®, TYSABRI®, and VUMERITY®

are registered trademarks of Biogen. BENEPALI , FLIXABI , and IMRALDI are trademarks of Biogen. COLUMVI®, EMPAVELI®, FAMPYRA , GAZYVA®, IQLIK , LEQEMBI®, LUNSUMIO®, OCREVUS®, SYFOVRE®, TOFIDENCE®, ZURZUVAE® and other trademarks referenced in this report are the property of their respective owners.

Digital Media Disclosure

From time to time we have used, or expect in the future to use, our investor relations website (investors.biogen.com), the Biogen LinkedIn account (linkedin.com/company/biogen-), and the Biogen X account (x.com/biogen) as a means of disclosing information to the public in a broad, non-exclusionary manner, including for purposes of the SEC's Regulation Fair Disclosure (Reg FD). Accordingly, investors should monitor our investor relations website and these social media channels in addition to our press releases, SEC filings, public conference calls and webcasts, as the information posted on them could be material to investors.

3

Alisha Alaimo

President, North America

Robin Kramer

Chief Financial Officer

Priya Singhal, M.D.,

M.P.H.

Head of Development

BIOGEN CALL PARTICIPANTS

Christopher A. Viehbacher

President and Chief Executive Officer

4

KEY HIGHLIGHTS

Christopher A. Viehbacher

President and

Chief Executive Officer

DELIVERING THE NEW BIOGEN THROUGH STRONG EXECUTION AND STRATEGIC ACTION

Growth Products*

New High Dose SPINRAZA

LEQEMBI IQLIK

SC-AI Initiation

Generated ~$850M for Q1 2026, up 12% YoY

Now Approved in the U.S.

• Under review in the U.S.,

  Japan and China

• U.S. PDUFA of May 24,

2026 (Priority Review)

Expands our commercial growth portfolio

Accelerates our path into nephrology

Significantly bolsters our growth outlook

Two marketed products

Provides U.S. infrastructure and expertise

Expected to:

• Be accretive in 2027

• Materially increase Biogen's Non-GAAP diluted EPS CAGR through the end of the decade

Obtained exclusive rights to felzartamab in greater China;

Biogen now owns exclusive worldwide rights for felzartamab

Note: LEQEMBI (lecanemab-irmb) is being developed in collaboration with Eisai Co., Ltd; SPIRNAZA and QALSODY is licensed from Ionis Pharmaceuticals

* Growth product revenue includes SKYCLARYS, QALSODY, ZURZUVAE, VUMERITY and SPINRAZA, plus Biogen's 50% share of net revenue and cost of sales, including royalties, from

the LEQEMBI Collaboration; CAGR = compound annual growth rate; SC-AI = subcutaneous autoinjector 6

THE APELLIS DEAL STRENGTHENS OUR EXPECTED EPS GROWTH OUTLOOK

2026

2030+

+ BIIB Late-stage Registrational Pipeline

Potential Biogen Non-GAAP EPS Profile

Illustrative, Not drawn to scale

+ Apellis marketed products

Expected to materially increase

Biogen's Non-GAAP diluted EPS CAGR

through the end of the decade

BIIB Consensus

Roughly flat through 2030*

Non-GAAP EPS projection not drawn to scale, intended to be used for illustrative purposes only

*Biogen Non-GAAP EPS consensus through 2030 per FactSet, accessed March 27, 2026 CAGR = compound annual growth rate

7

DEVELOPMENT UPDATE

Priya Singhal, M.D., M.P.H.

Head of Development

BUILDING MOMENTUM ACROSS MARKETED AND LATE-STAGE PIPELINE PROGRAMS

HD Spinraza now approved in the U.S.

New additional Phase 1b data at MDA

HD SPINRAZA*

50

50

Day 1 Day 15

28 mg

Q4M

Standard dose Nusinersen

12

12

12

12

Day 1 Day 15 Day 29 Day 60

12 mg

Q4M

• Data support the safety and effectiveness of salanersen over one year in children with SMA who previously received gene therapy

  
  
  

• Salanersen has the potential to transform the standard of care in SMA by delivering high efficacy with once-yearly dosing

  Litifilimab in CLE2

New real-world Leqembi persistence data presented at AD/PD

• Results show that ~78% and ~67% of individuals continued

  treatment at 18 and 24 months respectively

• Findings suggest a desire of patients to continue treating

Alzheimer's beyond just the removal of plaques

Received Breakthrough Therapy designation by the FDA

Second positive Phase 2 results presented at AAD

• Litifilimab met the primary endpoint of reduction of disease activity and showed rapid and continued skin improvement

LEQEMBI (lecanemab-irmb) is being developed in collaboration with Eisai Co., Ltd; SPIRNAZA and salanersen are licensed from Ionis Pharmaceuticals

1. Castro et al. MDA 2026; 2. Merola et al. AAD 2026; * Patients transitioning from standard dose to HD SPINRAZA will receive a single 50 mg loading dose prior to starting maintenance therapy (28 mg Q4M)

AAD = American Academy of Dermatology annual meeting; AD/PD = International Alzheimer's disease and Parkinson's disease conference; CLE = cutaneous lupus erythematosus; HD = High dose regimen of

SPINRAZA; MDA = muscular dystrophy association annual meeting; SMA = spinal muscular atrophy; Q4M = every 4 months 9

DAPIROLIZUMAB PEGOL

PHOENYCS FLY in SLE

ADVANCING TOWARD A MORE BALANCED, MULTI-ASSET GROWTH PROFILE

LEQEMBI

AHEAD 3-45 in Preclinical AD

SKYCLARYS Pediatric

BRAVE in FA

Neurology Immunology Rare Disease#

SALANERSEN

STELLAR-1 in SMA

Denotes new Biogen study in 2025-2026

FELZARTAMAB

TRANSCEND in AMR

FELZARTAMAB

TRANSPIRE in MVI

LITIFILIMAB

TOPAZ-1 in SLE

LITIFILIMAB

AMETHYST in CLE

FELZARTAMAB

PREVAIL in IgAN

LITIFILIMAB

TOPAZ-2 in SLE

ZOREVUNERSEN

EMPEROR in Dravet syndrome

FELZARTAMAB

PROMINENT in PMN

2026

2027

2028-2030

Note: Planned data flow, subject to change. LEQEMBI (lecanemab-irmb) is being developed in collaboration with Eisai Co; Zorevunersen is being developed in collaboration with Stoke Therapeutics, Inc.; Dapirolizumab pegol is being developed in collaboration with UCB; Salanersen is licensed from Ionis Pharmaceuticals, Inc. # Rare Disease is a commercial designation that includes multiple therapeutic indications. AD = Alzheimer's disease; AMR = antibody mediated rejection; CLE = cutaneous lupus erythematosus; FA = Friedreich ataxia; IgAN = IgA nephropathy; MVI = microvascular inflammation in

kidney transplant patients; PMN = primary membranous nephropathy; SC-AI = subcutaneous autoinjector; SLE = systemic lupus erythematosus; SMA = spinal muscular atrophy 10

KEY PIPELINE MILESTONES EXPECTED OVER THE NEXT 18 MONTHS

Litifilimab

High Dose

FDA Approval

SC-AI For Treatment Initiation

Felzartamab

Phase 3 readout in AMR

Litifilimab

Phase 3 readout in CLE

Salanersen

Phase 1b data

New Phase 2 CLE data

FDA PDUFA: May 24, 2026

Litifilimab

Two Phase 3 readouts in SLE

Zorevunersen

Phase 3 readout in Dravet syndrome

Q1 2026

Q2 2026

Q3 2026

Q4 2026

Q1 2027

Mid-year 2027

= Milestone achieved

BIIB091

Phase 2 readout

BIIB122

BIIB080

Phase 2 PoC readout

Phase 2 PoC readout

Neurology Immunology Rare Disease#

Note: Timeline is not comprehensive and reflects the estimated timing of data flow which is subject to change. LEQEMBI IQLIK (lecanemab-irmb) is being developed in collaboration with Eisai Co; SPIRNAZA, BIIB080, and Salanersen are licensed from Ionis Pharmaceuticals, Inc; Zorevunersen is being developed in collaboration with Stoke Therapeutics, Inc.; BIIB122 is being developed in collaboration with Denali Therapeutics, Inc; AMR = antibody mediated rejection; CLE = cutaneous lupus erythematosus; PoC = proof of concept; SC-AI = subcutaneous autoinjector; SLE = systemic lupus erythematosus; # Rare Disease

is a commercial designation that includes multiple therapeutic indications. 11

FINANCIAL UPDATE

Robin Kramer

Chief Financial Officer

FIRST QUARTER 2026 KEY FINANCIAL HIGHLIGHTS

$2.5B

2% YoY $2.15 31% YoY $3.57 18% YoY

• Revenue of $851M, up 12% YoY

• LEQEMBI WW in-market sales2: $168M; US: $86M; ROW: $82M

  Core OpEx3

• GAAP: $1.15B

• Non-GAAP: $1.08B

  Cash and Cashflow

• Generated $594M of free cash flow4

• $4.7B in cash and marketable securities and $1.5B of net debt as of March 31, 2026

  Proposed Apellis Transaction

• $41/share in cash in addition to a CVR

• Adds two commercial medicines, SYFOVRE and EMPAVELI, to our growth portfolio

  
  
  

• Expected to materially increase Biogen's Non-GAAP diluted EPS CAGR through the end of the decade

Our GAAP financial measures and a reconciliation of GAAP to Non-GAAP financial results are at the end of this presentation.

1. Growth product revenue includes SKYCLARYS, QALSODY, ZURZUVAE, VUMERITY and SPINRAZA, plus Biogen's 50% share of net revenue and cost of sales, including royalties, from the LEQEMBI Collaboration; 2. LEQEMBI in-market revenue booked by Eisai; 3. Core OpEx includes R&D and SG&A expenses; 4. Free cash flow, a non-GAAP financial measure = net cash flow from operations less capital

expenditures - see slide 16 for details; CAGR = compound annual growth rate; CVR = contingent value right; YoY = year-over-year 13

FIRST QUARTER 2026 REVENUE HIGHLIGHTS

Note: Revenue is shown in actual currency; Percent changes represented as favorable/(unfavorable) versus the prior year period; Numbers may not foot.

1. Includes Biogen's 50% share of net revenue and cost of sales, including royalties, from the LEQEMBI Collaboration; 2. Interferons includes: AVONEX and PLEGRIDY; 3. LEQEMBI In-market revenue booked by Eisai

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FIRST QUARTER 2026 KEY P&L ITEMS

The above table is not an income statement. Numbers do not foot. Percent changes represented as favorable/(unfavorable).

* Excluding amortization and impairment of acquired intangible assets. Our GAAP financial measures and a reconciliation of GAAP to Non-GAAP financial results are at the end of this presentation NMF = no meaningful number

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FIRST QUARTER 2026 CASH FLOW AND BALANCE SHEET

$646M

Cash flow from operations

$51M

Capital expenditures

$594M

Free cash flow*

$4.7B

$6.3B

$1.5B

Cash and marketable securities Debt

Net debt

Note: Numbers may not foot due to rounding

* Free cash flow, a non-GAAP financial measure = net cash flow from operations less capital expenditures

16

OUR BUSINESS MODEL AND FOOTPRINT POSITIONS US FOR POTENTIAL RESILIENCE IN UNCERTAIN ENVIRONMENTS

Does not include the impact from the proposed Apellis transaction

U.S. Product Revenue

Products which are largely manufactured in the U.S.

75%

25%

~75% of 2025 U.S. product revenue is

attributable to products which are largely manufactured in the U.S.

~50% of 2025 product revenue is

attributable to sales outside the U.S.

Total Product Revenue

U.S. ROW

50%

50%

Rare disease products

Core Pharmaceutical Revenue

67%

33%

~1/3 of 2025 core pharmaceutical

revenue is attributable to rare disease products

2025 U.S. Product Revenue

Commercial channels Government channels

60%

40%

~60% commercial, ~40% government

Product revenue includes TECFIDERA, VUMERITY, AVONEX, PLEGRIDY, TYSABRI, 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. 17

UPDATED GUIDANCE REFLECTS CONTINUED STRONG BUSINESS OUTLOOK AND INVESTMENT FOR GROWTH

Does not include the impact from the proposed Apellis transaction

Please see Biogen's Q1 2026 earnings release, available at the Investors section of Biogen's website at investors.biogen.com, for additional 2026 financial guidance assumptions.

This financial guidance does not include any impact from potential acquisitions or business development transactions, other than those noted here, or pending and future litigation or any impact of potential healthcare reform, as all are hard to predict. Biogen may incur charges, realize gains or losses, or experience other events or circumstances in 2026 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.

*Includes an expected approximately $0.55 Non-GAAP diluted EPS impact from the deal with TJ Biopharma for felzartamab Greater China region rights and an additional $0.25 Non-GAAP diluted EPS impact from a milestone expected to occur in the second quarter of 2026.

FY = full year

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KEY CONSIDERATIONS FOR FY 2026 FINANCIAL GUIDANCE

Does not include the impact from the proposed Apellis transaction

1. Growth products include SKYCLARYS, QALSODY, ZURZUVAE, VUMERITY and SPINRAZA, plus Biogen's 50% share of net revenue and cost of sales, including royalties, from the LEQEMBI Collaboration; 2.

Includes $100M upfront payment to TJ Bio and $45M from a milestone expected to occur in the second quarter of 2026

FY = full year; IPR&D = in-process research and development; MS = multiple sclerosis; OIE = Non-GAAP other (income) expense; OpEx = Non-GAAP R&D expense and Non-GAAP SG&A expense 19

APELLIS EXPECTED TO SIGNIFICANTLY STRENGTHEN OUR GROWTH PROFILE

Expect combined SYFOVRE and EMPAVELI revenue to grow in the mid- to high-teen percentage for at least the next two years

Transaction close expected in Q2 2026

Expect ~$120-130M OIE impact from financing costs and foregone interest income in 2026

Expect to de-lever by year-end 2027*

Expected to be accretive to Non-GAAP diluted EPS in 2027

Expected to materially increase Biogen's Non-GAAP diluted EPS CAGR through the end of the decade

* ~$2B of bank borrowings related to the Apellis transaction expected to be paid down by the end of 2027

CAGR = compound annual growth rate; OIE = other income and expense 20