Stockholders' Equity (Tables)

6 Months Ended

Jul. 31, 2019

A summary of stock option activity for the six months ended July 31, 2019 is as follows:



	Number of shares		Weighted average exercise price		Weighted average remaining contractual term (in years)	Aggregate intrinsic value
Options outstanding at January 31, 2019	12,961,397		$	19.43	5.4	$	1,161,695,032
Options granted	1,355,345		134.98
Options exercised	(1,014,592	)	6.81
Options forfeited/cancelled	(196,824	)	53.45
Options outstanding at July 31, 2019	13,105,326		$	31.85	5.4	$	1,756,820,772
Options vested and exercisable at July 31, 2019	6,478,882		$	5.83	3.6	$	1,037,073,153
Options vested and exercisable at July 31, 2019 and expected to vest thereafter	13,105,326		$	31.85	5.4	$	1,756,820,772

Summary of Restricted Stock Unit (RSU) Activity

A summary of restricted stock unit (RSU) activity for the six months ended July 31, 2019 is as follows:



	Unreleased restricted stock units		Weighted average grant date fair value
Balance at January 31, 2019	2,359,132		$	54.73
RSUs granted	226,058		135.39
RSUs vested	(644,003	)	50.78
RSUs forfeited/cancelled	(129,887	)	58.32
Balance at July 31, 2019	1,811,300		$	65.94

Schedule of Weighted-Average Assumptions Used to Estimate Grant Date Fair Value of Options Granted

The following table presents the weighted-average assumptions used to estimate the grant date fair value of options granted during the periods presented:



	Three months ended July 31,		Six months ended July 31,
	2019	2018	2019	2018
Volatility	41%	—%	41%	41%
Expected term (in years)	6.25	—	5.75 - 6.35	6.35
Risk-free interest rate	1.81% - 2.23%	—%	1.81% - 2.52%	2.73%
Dividend yield	—%	—%	—%	—%

CEO

Schedule of Weighted-Average Assumptions Used to Estimate Grant Date Fair Value of Options Granted

During the fiscal year ended January 31, 2018, we granted 2,838,635 stock options to our CEO. The stock option award is made up of five separate tranches. The first tranche vests over time, while the remaining four tranches vest based on certain stock price targets (market conditions). The grant date fair values of each tranche were calculated using a Monte Carlo simulation model. We have based our expected term on the historical stock activity behavior of our CEO. The following table provides the assumptions used in the Monte Carlo simulation for each tranche granted:



Volatility	41	%
Expected term (in years)	10.00
Risk-free interest rate	2.53	%
Dividend yield	—	%