United states securities and exchange commission

Table of Contents
BIOGEN INC. AND SUBSIDIARIES
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued)
F- 30
Estimated Future Amortization of Intangible Assets
 
Our amortization expense is based on the economic consumption and impairment of intangible assets. Our 
most significant intangible assets are related to our TECFIDERA, AVONEX and TYSABRI products. Annually, during our 
long-range planning cycle, we perform an analysis of anticipated lifetime revenues of TECFIDERA, AVONEX and 
TYSABRI. This analysis is also updated whenever events or changes in circumstances would significantly affect the 
anticipated lifetime revenues of any of these products.
Our most recent long-range planning cycle was completed in the third quarter of 2017. Based upon this 
analysis, the estimated future amortization of acquired intangible assets for the next five years is expected to be as 
follows:
(In millions)
As of December 31, 2017
2018
$
423.5
2019
401.8
2020
381.6
2021
254.3
2022
242.3
Goodwill
The following table provides a roll forward of the changes in our goodwill balance:
 
As of December 31,
(In millions)
2017
2016
Goodwill, beginning of year
$
3,669.3
$
2,663.8
Elimination of goodwill allocated to our hemophilia business
(314.1)
—
Increase to goodwill
1,267.3
1,026.9
Other
10.0
(21.4)
Goodwill, end of year
$
4,632.5
$
3,669.3
The elimination of goodwill represents an allocation based upon the relative enterprise fair value of the 
hemophilia business as of the distribution date. For additional information on the spin-off of our hemophilia 
business, please read Note 3, Hemophilia Spin-Off, to these consolidated financial statements.
The increase in goodwill during 2017 and 2016 was related to $1.5 billion and $1.2 billion in contingent 
milestones achieved (exclusive of $232.7 million and $173.1 million in tax benefits), respectively, and payable to the 
former shareholders of Fumapharm AG or holders of their rights. 
Other includes changes related to foreign currency exchange rate fluctuations. As of December 31, 2017, we 
had no accumulated impairment losses related to goodwill.
 For additional information on future contingent payments to the former shareholders of Fumapharm AG or 
holders of their rights, please read Note 22, Commitments and Contingencies, to these consolidated financial 
statements.

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Table of Contents
BIOGEN INC. AND SUBSIDIARIES
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued)
F- 31
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:
(In millions)
As of
December 31,
2017
Quoted
Prices in
Active
Markets
(Level 1)
Significant
Other
Observable
Inputs
(Level 2)
Significant
Unobservable
Inputs
(Level 3)
Assets:
Cash equivalents
$
1,229.4 $
— $
1,229.4 $
—
Marketable debt securities:
Corporate debt securities
2,609.8
—
2,609.8
—
Government securities
1,919.3
—
1,919.3
—
Mortgage and other asset backed securities
643.4
—
643.4
—
Marketable equity securities
11.8
11.8
—
—
Derivative contracts
2.7
—
2.7
—
Plan assets for deferred compensation
28.5
—
28.5
—
Total
$
6,444.9 $
11.8 $
6,433.1 $
—
Liabilities:
Derivative contracts
$
111.3 $
— $
111.3 $
—
Contingent consideration obligations
523.6
—
—
523.6
Total
$
634.9 $
— $
111.3 $
523.6
(In millions)
As of
December 31,
2016
Quoted
Prices
in Active
Markets
(Level 1)
Significant
Other
Observable
Inputs
(Level 2)
Significant
Unobservable
Inputs
(Level 3)
Assets:
Cash equivalents
$
2,039.6 $
— $
2,039.6 $
—
Marketable debt securities:
Corporate debt securities
2,663.8
—
2,663.8
—
Government securities
2,172.5
—
2,172.5
—
Mortgage and other asset backed securities
561.7
—
561.7
—
Marketable equity securities
24.9
24.9
—
—
Derivative contracts
61.0
—
61.0
—
Plan assets for deferred compensation
34.5
—
34.5
—
Total
$
7,558.0 $
24.9 $
7,533.1 $
—
Liabilities:
Derivative contracts
$
13.6 $
— $
13.6 $
—
Contingent consideration obligations
467.6
—
—
467.6
Total
$
481.2 $
— $
13.6 $
467.6
The fair value of Level 2 instruments classified as cash equivalents and marketable debt securities were 
determined through third-party pricing services. For a description of our validation procedures related to prices 
provided by third-party pricing services, please read Note 1, Summary of Significant Accounting Policies: Fair Value 
Measurements, to these consolidated financial statements.

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Table of Contents
BIOGEN INC. AND SUBSIDIARIES
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued)
F- 32
Debt Instruments
The fair values of our debt instruments, which are Level 2 liabilities, are summarized as follows:
 
As of December 31,
(In millions)
2017
2016
Notes payable to Fumedica
$
3.2
$
6.1
6.875% Senior Notes due March 1, 2018
—
583.7
2.900% Senior Notes due September 15, 2020
1,517.7
1,521.5
3.625% Senior Notes due September 15, 2022
1,032.9
1,026.6
4.050% Senior Notes due September 15, 2025
1,851.9
1,796.0
5.200% Senior Notes due September 15, 2045
2,077.6
1,874.5
Total
$
6,483.3
$
6,808.4
In November 2017 we redeemed our 6.875% Senior Notes due March 1, 2018 with an aggregate principal 
amount of $550.0 million. For information on this redemption please read Note 12, Indebtedness, to these 
consolidated financial statements.
The fair value of our notes payable to Fumedica was estimated using market observable inputs, including 
current interest and foreign currency exchange rates. The fair value of each series of our Senior Notes was 
determined through market, observable and corroborated sources. For additional information on our debt 
instruments, please read Note 12, Indebtedness, to these consolidated financial statements.
Contingent Consideration Obligations
In connection with our acquisitions of Convergence, Stromedix and BIN in 2015, 2012 and 2010, respectively, 
we agreed to make additional payments based upon the achievement of certain milestone events. The following 
table provides a roll forward of the fair values of our contingent consideration obligations, which includes Level 3 
measurements:
 
As of December 31,
(In millions)
2017
2016
Fair value, beginning of year
$
467.6
$
506.0
Changes in fair value
62.7
14.8
Payments and other
(6.7)
(53.2)
Fair value, end of year
$
523.6
$
467.6
 
As of December 31, 2017 and 2016, approximately $279.0 million and $246.8 million, respectively, of the fair 
value of our total contingent consideration obligations was reflected as a component of other long-term liabilities in 
our consolidated balance sheets with the remaining balance reflected as a component of accrued expenses and 
other. Changes in the fair value of our contingent consideration obligations are primarily due to changes in the 
expected timing and probabilities of success related to the achievement of certain developmental milestones and 
changes in the discount rate. Payments and other for 2016 includes $7.9 million of a Convergence milestone 
converted to a short-term obligation under the acquisition agreement.
There were no changes in valuation techniques or transfers between fair value measurement levels during the 
years ended December 31, 2017 and 2016. The fair values of the intangible assets and contingent consideration 
liabilities were based on a probability-adjusted discounted cash flow calculation using Level 3 fair value 
measurements and inputs including estimated revenues and probabilities of success. For additional information on 
the valuation techniques and inputs utilized in the valuation of our financial assets and liabilities, please read Note 
1, Summary of Significant Accounting Policies, to these consolidated financial statements.

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