In January 2015, our board of directors adopted the 2015 Equity Incentive Plan (2015 Plan), which became effective prior to the completion of our initial public offering (IPO). A total of 12,200,000 shares of Class A common stock was initially reserved for issuance pursuant to future awards under the 2015 Plan. On the first day of each fiscal year, shares available for issuance are increased based on the provisions of the 2015 Plan. Any shares subject to outstanding awards under our 2006 Equity Incentive Plan or 2011 Equity Incentive Plan that are cancelled or repurchased subsequent to the 2015 Plan’s effective date are returned to the pool of shares reserved for issuance under the 2015 Plan. Awards granted under the 2015 Plan may be (i) incentive stock options, (ii) nonstatutory stock options, (iii) restricted stock units, (iv) restricted stock awards or (v) stock appreciation rights, as determined by our board of directors at the time of grant. Generally, our restricted stock units vest over four years and, (a) for employee new hire restricted stock unit grants, twenty-five percent vest one year from the vesting commencement date and continue to vest 1/16th per quarter thereafter; or (b) for employee refresh restricted stock unit grants, 1/16th per quarter vest from the vesting commencement date. As of October 31, 2020, 22,898,009 shares were reserved for future issuance under the 2015 Plan.

In January 2015, our board of directors adopted the 2015 Employee Stock Purchase Plan (2015 ESPP), which became effective prior to the completion of our IPO. A total of 2,500,000 shares of Class A common stock was initially reserved for issuance under the 2015 ESPP. On the first day of each fiscal year, shares available for issuance are increased based on the provisions of the 2015 ESPP. The 2015 ESPP allows eligible employees to purchase shares of our Class A common stock at a discount of up to 15% through payroll deductions of their eligible compensation, subject to any plan limitations. The 2015 ESPP provides for 24-month offering periods beginning March 16 and September 16 of each year, and each offering period consists of four six-month purchase periods.

On each purchase date, eligible employees may purchase our stock at a price per share equal to 85% of the lesser of (1) the fair market value of our stock on the offering date or (2) the fair market value of our stock on the purchase date. In the event the price is lower on the last day of any purchase price period, in addition to using that price as the basis for that purchase period, the offering period resets and the new lower price becomes the new offering price for a new 24 month offering period. As of October 31, 2020, 1,288,378 shares were reserved for future issuance under the 2015 ESPP.

The following table summarizes the stock option activity under the equity incentive plans and related information:

	Shares Subject to Options Outstanding					Weighted- Average
				Weighted-		Remaining
				Average Exercise		Contractual Life		Aggregate
	Shares			Price		(Years)		Intrinsic Value
								(in thousands)
Balance as of January 31, 2020		8,772,585		$	9.48		4.27	$	60,221
Options granted		31,666			12.48
Options exercised		(1,830,313	)		5.39
Options forfeited/cancelled		(182,213	)		10.35
Balance as of October 31, 2020		6,791,725		$	10.57		3.96	$	42,880
Vested and expected to vest as of October 31, 2020		6,727,337		$	10.49		3.92	$	42,876
Exercisable as of October 31, 2020		5,455,872		$	8.31		3.02	$	42,803

The aggregate intrinsic value of options vested and expected to vest and exercisable as of October 31, 2020 is calculated based on the difference between the exercise price and the current fair value of our common stock. The aggregate intrinsic value of exercised options for the nine months ended October 31, 2020 and 2019 was $25.4 million and $4.5 million, respectively. The aggregate estimated fair value of stock options granted to employees that vested during the nine months ended October 31, 2020 and 2019 was $1.9 million and $2.4 million, respectively. The weighted-average grant date fair value of options granted to employees during the nine months ended October 31, 2020 and 2019 was $5.41 and $8.00 per share, respectively.

As of October 31, 2020, there was $2.5 million of unrecognized stock-based compensation expense related to outstanding stock options granted to employees that is expected to be recognized over a weighted-average period of 1.59 years.

To further align our stockholders’ interests with executive officers’ interests, the Compensation Committee of our board of directors approved and granted performance-based stock options with market-based performance goals under the 2015 Plan to certain executive officers, which are subject to both the achievement of the market-based performance goal established by the Compensation Committee and the continued employment of the participant. These performance-based stock options vest only to the extent that both the market-based performance goal and time-based condition are satisfied. The market-based performance goal will be satisfied if, before the four-year anniversary of the grant date, the closing price of our Class A common stock is maintained at or above a pre-determined share price for a period of 30 consecutive trading days. The time-based vesting condition will be satisfied over the following four-year schedule: Twenty-five percent of the option’s time-based vesting condition is satisfied one year from the vesting commencement date and the remaining 1/48th of the option’s time-based vesting condition is satisfied monthly thereafter, subject to continued employment through each such date. As of October 31, 2020, the total outstanding balance of performance-based stock options was 1,375,000.

The grant date fair value of these awards was determined using a Monte Carlo valuation model and the related stock-based compensation expense is recognized based on an accelerated attribution method. Of the total $2.5 million in unrecognized stock-based compensation expense for stock options as of October 31, 2020, $1.4 million related to outstanding performance-based stock options with market-based performance goals, which is expected to be recognized over a weighted-average period of 2.09 years.

The following table summarizes the restricted stock unit activity under the equity incentive plans and related information:

	Number of			Weighted-
	Restricted			Average
	Stock Units			Grant Date
	Outstanding			Fair Value
Unvested balance - January 31, 2020		21,808,107		$	18.85
Granted		9,766,239			15.59
Vested, net of shares withheld for employee payroll taxes		(4,057,217	)		18.32
Forfeited/cancelled		(2,838,306	)		18.84
Unvested balance - October 31, 2020		24,678,823		$	17.65

As of October 31, 2020, there was $270.7 million of unrecognized stock-based compensation expense related to outstanding restricted stock units granted to employees that is expected to be recognized over a weighted-average period of 2.69 years.

We use performance-based incentives for certain employees, including our named executive officers, to achieve our annual financial and operational objectives, while making progress towards our longer-term strategic and growth goals. Typically, near the beginning of each fiscal year, our Compensation Committee adopts the performance criteria and targets for the incentive compensation plan for that fiscal year, which identifies the plan participants, the performance measures and the associated target levels for each measure, and the potential payouts based on actual performance for the fiscal year.

In the first quarter of fiscal year 2020, our Compensation Committee adopted and approved the performance criteria and targets for fiscal year 2020 under our omnibus Executive Incentive Plan (the Fiscal 2020 Executive Bonus Plan). Based on a review of our actual achievement of pre-established corporate financial objectives and additional inputs from our Compensation Committee, the Fiscal 2020 Executive Bonus Plan was determined, settled and paid out in the first quarter of fiscal year 2021 in the form of fully vested restricted stock units. During the first quarter of fiscal year 2021, we recognized stock-based compensation expense related to the Fiscal 2020 Executive Bonus Plan in the amount of $1.5 million.

In the first quarter of fiscal year 2021, our Compensation Committee adopted and approved the performance criteria and targets for fiscal year 2021 under our omnibus Executive Plan (the Fiscal 2021 Executive Bonus Plan). The Fiscal 2021 Executive Bonus Plan provides opportunities for 100% equity incentive compensation payouts based on our actual achievement of pre-established corporate financial objectives, subject to review and a final approval by our Compensation Committee. During the nine months ended October 31, 2020, we recognized stock-based compensation expense related to the Fiscal 2021 Executive Bonus Plan in the amount of $7.0 million. The unrecognized compensation expense related to the ungranted and unvested Fiscal 2021 Executive Bonus Plan is $4.1 million, based on the expected performance against the pre-established corporate financial objectives as of October 31, 2020, which is expected to be recognized over a remaining weighted-average period of less than one year. The payouts of the Fiscal 2021 Executive Bonus Plan are expected to be made in the form of fully vested restricted stock units in the first quarter of fiscal year 2022.

As of October 31, 2020, there was $38.3 million of unrecognized stock-based compensation expense related to the 2015 ESPP that is expected to be recognized over the remaining term of the respective offering periods. During the first quarter of fiscal year 2021, the fair market value of our stock on the purchase date (i.e., March 15, 2020) was lower than the fair market value of our stock on certain offering dates. As a result, certain offering periods reset and the new lower price became the new offering price for a new 24 month offering period. These resets resulted in a change in fair value and a corresponding incremental stock-based compensation expense initially totaling $3.9 million, which is expected to be recognized over the term of the new offering period.

The following table summarizes the components of stock-based compensation expense recognized in the condensed consolidated statements of operations (in thousands):

	Three Months Ended				Nine Months Ended
	October 31,				October 31,
	2020		2019		2020		2019
Cost of revenue	$	4,731	$	4,428	$	13,673	$	12,399
Research and development		14,581		16,653		46,139		44,878
Sales and marketing		10,619		9,250		31,364		28,644
General and administrative		7,903		7,427		24,262		21,004
Total stock-based compensation	$	37,834	$	37,758	$	115,438	$	106,925

We estimated the fair value of employee stock options and 2015 ESPP purchase rights using a Black-Scholes option pricing model with the following assumptions.

	Three Months Ended										Nine Months Ended
	October 31,										October 31,
	2020					2019					2020					2019
Employee Stock Options
Expected term (in years)				N/A					N/A						5.8		5.5	-		5.8
Risk-free interest rate				N/A					N/A					0.6%					1.8%
Volatility				N/A					N/A					46%					45%
Dividend yield				N/A					N/A					0%					0%
Employee Stock Purchase Plan
Expected term (in years)		0.5	-		2.0		0.5	-		2.0		0.5	-		2.0		0.5	-		2.0
Risk-free interest rate				0.1%		1.7%		-	1.9%		0.1%		-	0.4%		1.7%		-	2.5%
Volatility	48%		-	54%		34%		-	47%		44%		-	54%		34%		-	55%
Dividend yield				0%					0%					0%					0%

The assumptions used in the Black-Scholes option pricing model were determined as follows:

Fair Value of Common Stock. We use the market closing price for our Class A common stock as reported on the New York Stock Exchange to determine the fair value of our common stock at each grant date.

Expected Term. The expected term represents the period that our share-based awards are expected to be outstanding. The expected term assumptions were determined based on the vesting terms, exercise terms and contractual lives of the options and 2015 ESPP purchase rights.

Expected Volatility. We estimate the expected volatility of the stock option grants and 2015 ESPP purchase rights based on the historical volatility of our Class A common stock over a period equivalent to the expected term of the stock option grants and 2015 ESPP purchase rights, respectively.

Risk-free Interest Rate. The risk-free rate that we use is based on the implied yield available on U.S. Treasury zero-coupon issues with remaining terms similar to the expected term on the options and 2015 ESPP purchase rights.

Dividend Yield. We have never declared or paid any cash dividends and do not plan to pay cash dividends in the foreseeable future, and, therefore, use an expected dividend yield of zero.