Total share-based compensation included in net income for the years ended January 1, 2021, December 27, 2019, and December 28, 2018 is as follows:

	Year Ended
	January 1,		December 27,		December 28,
	2021		2019		2018
Restricted stock units	$	8,676	$	6,762	$	7,053
Common stock subject to vesting requirements		1,064		954		2,027
	$	9,740	$	7,716	$	9,080

The number of shares available for future issuance under the Company's stock plans as of January 1, 2021 were 2,052,508. The Company issues new shares as they are required to be delivered under the plan.

The Company has granted stock options to employees and directors of the Company at exercise prices equal to the fair value of the stock at the date of grant. The options generally vest ratably over four years, based on continued employment, with a maximum term of ten years. Stock option activity under the Company’s stock option plans for the year ended January 1, 2021 is summarized as follows:

	Option Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of December 27, 2019		180,000	$	4.00
Exercised		—		—
Forfeited or expired		—		—
Outstanding as of January 1, 2021		180,000	$	4.00		1.21	$	1,870,200
Exercisable at January 1, 2021		180,000	$	4.00		1.21	$	1,870,200

A summary of the Company’s stock option activity for the years ended December 27, 2019 and December 28, 2018 was as follows:

	December 27, 2019					December 28, 2018
	Option Shares			Weighted Average Exercise Price		Option Shares		Weighted Average Exercise Price
Outstanding at beginning of year		180,167		$	4.00		180,167	$	4.00
Exercised		—			—		—		—
Forfeited or expired		(167	)		3.63		—		—
Outstanding at end of year		180,000		$	4.00		180,167	$	4.00
Exercisable at end of year		180,000		$	4.00		180,167	$	4.00

The fair value of the SARs and stock options is estimated using the Black-Scholes option pricing valuation model. The determination of fair value is affected by the Company's stock price, expected stock price volatility, expected term of the award and the risk-free rate of interest.

	Number of SARs		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding as of December 27, 2019		2,916,563	$	4.00		1.10
Expired		—		—		—
Outstanding as of January 1, 2021		2,916,563	$	4.00	$	1.10
Exercisable at January 1, 2021		2,916,563	$	4.00	$	1.10

Under the stock plans, participants may be granted restricted stock units, each of which represents a conditional right to receive a common share in the future. The restricted stock units granted under this plan generally vest over one of the following vesting schedules: (1) a four -year period, with 50% vesting on the second anniversary and 25% of the shares vesting on the third and fourth anniversaries of the grant date, (2) a four -year period, with 25% vesting on the first, second, third and fourth anniversary, (3) a three -year period with 33% vesting on the first, second and third anniversary, or (4) a one-year period with 100% vest on the first anniversary. Upon vesting, the restricted stock units will convert into an equivalent number of shares of common stock. The amount of expense relating to the restricted stock units is based on the closing market price of the Company’s common stock on the date of grant and is amortized on a straight-line basis over the applicable requisite service period. Restricted stock unit activity for the year ended January 1, 2021, was as follows:

	Number of Restricted Stock Units			Weighted Average Grant-Date Fair Value
Nonvested balance as of December 27, 2019		1,042,543			17.34
Granted		646,659			15.43
Vested		(464,932	)		16.93
Forfeited		(33,083	)		17.15
Nonvested balance as of January 1, 2021		1,191,187		$	16.47

The Company recorded restricted stock units based compensation expense of $8.7 million, $6.8 million and $7.1 million in 2020, 2019, and 2018 respectively, which is included in stock compensation expense, based on the vesting provisions of the restricted stock units and the fair value of the stock on the grant date. As of January 1, 2021, there was $11.1 million of total restricted stock unit compensation expense related to the unvested awards not yet recognized, which is expected to be recognized over a weighted average period of 2.3 years. The Company accounts for certain restricted stock units under liability accounting as a result of the fixed monetary amount and a variable number of shares that will be issued.

Shares of common stock subject to vesting requirements were issued to employees of acquired companies. These shares vest over a period of up to four years. Compensation expense was based on the fair value of the Company’s common stock at the time of grant and is recognized on a straight-line basis. The activity for common stock subject to vesting requirements for the year ended January 1, 2021 was as follows:

	Number of Shares of Common Stock Subject to Vesting Requirements			Weighted Average Grant-Date Fair Value
Nonvested balance as of December 27, 2019		128,791		$	18.64
Granted		—			—
Vested		(59,797	)		18.84
Forfeited		(2,318	)		17.38
Nonvested balance as of January 1, 2021		66,676		$	18.51

Common stock subject to vesting requirements of $1.0 million was issued in 2019 in relation to acquisitions. These shares are subject to up to a four-year vesting period.

The Company recorded compensation expense of $1.1 million, $1.0 million and $2.0 million, during the years ended January 1, 2021, December 27, 2019, and December 28, 2018 respectively, related to common stock subject to vesting requirements.

As of January 1, 2021, there was $0.5 million of total stock-based compensation expense related to common stock granted subject to vesting requirements not yet recognized, which is expected to be recognized over a weighted average period of 0.9 years.