The ACCO Brands Corporation Incentive Plan (the "Plan") provides for stock based awards generally in the form of stock options, restricted stock units ("RSUs") and performance stock units ("PSUs"), any of which may be granted alone or with other types of awards and dividend equivalents. A total of up to 11,775,000 shares may be issued under awards to key employees and non-employee directors under the Plan.

Beginning in 2018, the Company initiated a cash dividend to stockholders and began accruing dividend equivalents (“DEs") on all outstanding RSUs and PSUs as permitted by the Plan. DEs entitle holders of RSUs and PSUs to the same dividend value per share as holders of common stock. RSUs and PSUs are credited with DEs that are converted to RSUs and PSUs at the fair market value of our common stock on the dates the dividend payments are made and are subject to the same terms and conditions as the underlying award. DEs credited to RSUs and PSUs will only be paid to the extent the awards vest and any performance goals are achieved.

The following table summarizes the impact of all stock-based compensation expense on our Consolidated Statements of Income for the years ended December 31, 2020, 2019 and 2018:


(in millions)	2020		2019		2018
Selling, general and administrative expense	$	6.5	$	10.1	$	8.8
Loss before income tax	(6.5)		(10.1)		(8.8)
Income tax benefit	(1.6)		(2.4)		(2.2)
Net loss	$	(4.9)	$	(7.7)	$	(6.6)


(in millions)	2020		2019		2018
Stock option compensation expense	$	2.7	$	2.7	$	2.0

RSU compensation expense	5.2		5.1		4.7
PSU compensation expense	(1.4)		2.3		2.1
Total stock-based compensation expense	$	6.5	$	10.1	$	8.8

The exercise price of each stock option equals or exceeds the fair market price of our stock on the date of grant. Options granted prior to 2020 can generally be exercised over a maximum term of up to seven years and starting in 2020 options can generally be exercised over a maximum term of up to ten years. Stock options outstanding as of December 31, 2020, generally vest ratably over three years from the grant date. The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model and the weighted average assumptions as outlined in the following table:


	Year Ended December 31,
	2020			2019			2018
Weighted average expected lives	6.0		years	4.6		years	4.8		years
Weighted average risk-free interest rate	0.81		%	2.49		%	2.62		%
Weighted average expected volatility	36.0		%	36.1		%	36.4		%
Expected dividend yield	3.16		%	2.65		%	1.87		%
Weighted average grant date fair value	$	2.03		$	2.40		$	3.76

Volatility is calculated using ACCO Brands' historic volatility. The weighted average expected option term reflects the application of the simplified method, which defines the life as the average of the contractual term of the option and the weighted average vesting period for options granted in 2020. The weighted average expected option term reflects ACCO Brands' historic life for all options granted prior to 2020. The risk-free interest rate for the expected term of the option is based on the U.S. Treasury yield curve in effect at the time of grant.


	Number Outstanding	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Outstanding at December 31, 2019	4,417,693	$	9.32
Granted	1,437,188	$	8.25
Exercised	(683,718)	$	6.49
Forfeited	(208,278)	$	9.43
Outstanding at December 31, 2020	4,962,885	$	9.40	5.0 years	$	1.7	million

Exercisable shares at December 31, 2020	2,564,242	$	9.84	2.7 years	$	1.4	million

We received cash of $4.4 million, $4.2 million and $6.8 million from the exercise of stock options during the years ended December 31, 2020, 2019 and 2018, respectively. The aggregate intrinsic value of options exercised during the years ended December 31, 2020, 2019 and 2018 totaled $1.6 million, $1.0 million and $4.1 million, respectively.

The fair value of options vested during the years ended December 31, 2020, 2019 and 2018 was $2.7 million, $1.9 million and $2.3 million, respectively. As of December 31, 2020, we had unrecognized compensation expense related to stock options of $3.3 million, which will be recognized over a weighted-average period of 1.7 years.

RSUs vest over a pre-determined period of time, generally three years from the date of grant. Stock-based compensation expense for the years ended December 31, 2020, 2019 and 2018 includes $0.9 million, $1.1 million and $1.1 million, respectively, of expense related to shares of stock (included in RSU compensation expense) which were RSUs granted to non-employee directors as a component of their compensation. The non-employee director RSUs became fully vested on the grant date. PSUs also vest over a pre-determined period of time, generally not longer than three years, but are further subject to the achievement of certain business performance criteria being met during the three-year performance period. Based upon the level of achieved performance, the number of shares actually awarded can vary from 0% to 200% of the original grant.

There were 2,050,085 RSUs outstanding as of December 31, 2020. All outstanding RSUs as of December 31, 2020 vest within three years of their date of grant. We generally recognize compensation expense for our RSU awards ratably over the service period. Upon vesting, all of the RSU awards will be converted into the right to receive one share of common stock of the Company for each unit that vests. The cost of these awards is determined using the fair value of the shares on the date of grant, and compensation expense is generally recognized over the period during which the employee provides the requisite service to the Company.


	Stock Units	Weighted Average Grant Date Fair Value
Outstanding at December 31, 2019	1,716,445	$	10.53
Granted	724,319	$	7.92
Vested and distributed	(323,818)	$	12.49

Forfeited and cancelled	(66,861)	$	10.20
Outstanding at December 31, 2020	2,050,085	$	9.31
Vested and deferred at December 31, 2020(1)	613,853	$	8.82

For the years ended December 31, 2019 and 2018, we granted 679,601 and 465,378 RSUs, respectively. The weighted-average grant date fair value of our RSUs was $7.92, $8.74, and $12.71 for the years ended December 31, 2020, 2019 and 2018, respectively. The fair value of RSUs that vested during the years ended December 31, 2020, 2019 and 2018 was $4.7 million, $3.6 million and $4.7 million, respectively. As of December 31, 2020, we have unrecognized compensation expense related to RSUs of $5.7 million, which will be recognized over a weighted-average period of 1.8 years.


	Stock Units	Weighted Average Grant Date Fair Value
Outstanding at December 31, 2019	1,021,543	$	9.98
Granted	939,529	$	8.25
Vested	(377,073)	$	12.75
Forfeited and cancelled	(67,145)	$	8.56
Other - decrease due to performance of PSUs	(1,516,854)	$	8.28
Outstanding at December 31, 2020	—	$	—

For the years ended December 31, 2019 and 2018, we granted 895,389 and 747,996 PSUs, respectively. For the years ended December 31, 2020, 2019 and 2018, 377,073, 1,059,825 and 1,327,613 PSUs vested, respectively. The weighted-average grant date fair value of our PSUs was $8.25, $8.35, and $12.82 for the years ended December 31, 2020, 2019 and 2018, respectively. The fair value of PSUs that vested during the years ended December 31, 2020, 2019 and 2018 was $4.8 million, $8.1 million and $10.0 million respectively. Based on the level of achievement of the performance targets associated with the