Stock Option Plans (Tables)

6 Months Ended

Jun. 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		(1,509	)		1,509			-			3.12
Options exercised		-			(9	)		-			2.66
Restricted stock units vested		-			-			(25	)		n/a
Options forfeited/cancelled		410			(590	)		-			4.02
June 30, 2017		7,795			7,868			75		$	3.49
Options exercisable at June 30, 2017					3,811					$	3.74

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 noted in the following table:

	Six Months Ended June 30,
	2017			2016
Expected life (in years)		6.08			6.07
Risk-free interest rates		1.92	%		1.45	%
Volatility		59.80	%		61.78	%
Dividend yield		-	%		-	%

Schedule of stock based compensation expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Research and development	$	166	$	579	$	496	$	1,785
General and administrative		739		1,641		1,434		3,808
Total stock-based compensation expense	$	905	$	2,220	$	1,930	$	5,593