Stock Option Plans (Tables)

9 Months Ended

Sep. 30, 2017

Stock Option Plans [Abstract]

Summary of stock option activity

A summary of BioTime's 2012 Plan activity and related information follows (in thousands, except per share amounts):

	Shares Available for Grant			Number of Options Outstanding			Number of RSUs Outstanding			Weighted Average Exercise Price of Options
December 31, 2016		2,894			6,958			100		$	3.60
Increase to the 2012 Plan option pool		6,000			-			-			-
Options granted		(1,762	)		1,762			-			3.11
Options exercised		-			(9	)		-			2.66
Restricted stock units vested		-			-			(31	)		-
Options forfeited/cancelled		426			(606	)		-			3.99
September 30, 2017 (1)		7,558			8,105			69		$	3.47
Options exercisable at September 30, 2017					4,072					$	3.71

⁽¹⁾On October 13, 2017, BioTime’s Board of Directors (the “Board”) determined to temporarily set a limit on shares available for grants of share-based awards pursuant to the 2012 Plan. While that limit remains in place, BioTime will not grant share-based awards for more than a total of approximately 2.5 million of the common shares remaining available for awards under the 2012 Plan.

Schedule of weighted average assumptions to calculate fair value of stock options

The fair value of each option award is estimated on the date of grant using a Black-Scholes option pricing model applying the weighted-average assumptions in the following table:

	Nine Months Ended September 30,
	2017			2016
Expected life (in years)		5.47			4.97
Risk-free interest rates		1.78	%		1.43	%
Volatility		59.04	%		60.77	%
Dividend yield		-	%		-	%

Schedule of stock based compensation expense

Operating expenses include stock-based compensation expense as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
		2017	2016		2017		2016
Research and development	$	326	$	237	$	822	$	2,022
General and administrative		647		473		2,081		4,281
Total stock-based compensation expense	$	973	$	710	$	2,903	$	6,303