As of March 31, 2020, the 2005 Incentive Plan (as amended) has a total reserve of 27,783,379 shares of which 4,662,468 shares are available for issuance.

Stock-based compensation is based on the estimated fair value of awards, net of estimated forfeitures, and recognized over the requisite service period. Estimated forfeitures are based on historical experience at the time of grant and may be revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The stock-based compensation related to all of our stock-based awards and employee stock purchases for the three months ended March 31, 2020 and 2019 is as follows (in thousands):


	Three Months Ended March 31,
	2020		2019
Cost of net revenues	$	1,347	$	1,112
Selling, general and administrative	18,130		16,890

Research and development	3,450		3,042
Total stock-based compensation	$	22,927	$	21,044

The fair value of RSUs is based on our closing stock price on the date of grant. A summary for the three months ended March 31, 2020 is as follows:


	Number of Shares Underlying RSUs (in thousands)	Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Unvested as of December 31, 2019	696	$	190.60
Granted	251	272.24
Vested and released	(259)	145.91
Forfeited	(11)	233.45
Unvested as of March 31, 2020	677	$	237.27	1.8	$	117,738

As of March 31, 2020, we expect to recognize $133.4 million of total unamortized compensation cost, net of estimated forfeitures, related to RSUs over a weighted average period of 2.7 years.

We grant MSUs to our executive officers. Each MSU represents the right to one share of Align’s common stock. The actual number of MSUs which will be eligible to vest will be based on the performance of Align’s stock price relative to the

performance of a stock market index over the vesting period, and certain MSU grants are also based on Align’s stock price at the end of the performance period. The maximum number of MSUs which will be eligible to vest range from 250% to 300% of the MSUs initially granted and the vesting period is three years.


	Number of Shares Underlying MSUs (in thousands)	Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Unvested as of December 31, 2019	244	$	331.35
Granted	156	242.04
Vested and released	(173)	120.39

Unvested as of March 31, 2020	227	$	430.50	1.9	$	39,529

As of March 31, 2020, we expect to recognize $52.9 million of total unamortized compensation cost, net of estimated forfeitures, related to MSUs over a weighted average period of 1.9 years.

In May 2010, our shareholders approved the 2010 Employee Stock Purchase Plan (the “2010 Purchase Plan”) which will continue until terminated by either the Board of Directors or its administrator. The maximum number of shares available for purchase under the 2010 Purchase Plan is 2,400,000 shares. As of March 31, 2020, we have 379,304 shares available for future issuance.

The fair value of the option component of the 2010 Purchase Plan shares was estimated at the grant date using the Black-Scholes option pricing model with the following weighted average assumptions:


	Three Months Ended March 31,
	2020			2019
Expected term (in years)	1.0			1.4
Expected volatility	41.7		%	48.6		%
Risk-free interest rate	1.5		%	2.5		%
Expected dividends	—			—
Weighted average fair value at grant date	$	80.54		$	90.36

As of March 31, 2020, there was $8.4 million of total unamortized compensation costs related to employee stock purchases which we expect to be recognized over a weighted average period of 0.7 year.