20. Stock-Based Compensation

During the year-to-date period ended September 29, 2017, the Company granted stock-based compensation awards under the Amended and Restated 2008 Long Term Performance Plan in the form of stock options, restricted stock units and performance units. The stock-based compensation awards granted during the year-to-date period ended September 29, 2017 are further discussed below.

Stock Options. During the quarterly period ended March 31, 2017, the Company granted 363,939 stock options with a weighted average exercise price of $168.80 per option, which was equal to the closing price of L3’s common stock on the date of grant. The options expire 10 years after the date of grant and vest ratably over a three-year period on the annual anniversary of the date of grant. The options granted to the Company’s Chairman and Chief Executive Officer are also subject to performance-based vesting conditions. The weighted average grant date fair value for the options of $27.18 per option was estimated using the Black-Scholes option-pricing model. The weighted average assumptions used in the valuation model for this grant are presented in the table below.

First Quarter Ended March 31, 2017
Expected holding period (in years)	5.2
Expected volatility	20.1	%
Expected dividend yield	2.0	%
Risk-free interest rate	2.0	%

Restricted Stock Units. During the first half period ended June 30, 2017, the Company granted 293,032 restricted stock units with a weighted average grant date fair value of $168.77 per share. Restricted stock units typically vest three years after the grant date for employees and one year after the grant date for non-employee directors, or if earlier, on the date of the first annual stockholders meeting held after the grant date. The restricted stock units automatically convert into shares of L3’s common stock upon vesting. The grant date fair value of the restricted stock unit awards is based on L3’s closing stock price at the date of grant and is generally recognized as compensation expense on a straight-line basis over the vesting period. However, for employees who attain retirement eligibility status prior to the end of the three-year cliff vesting period and who have provided at least one year of service after the date of grant, compensation expense is recognized over the shorter period from the date of grant to the retirement eligibility date. For grants of restricted stock units made during the year-to-date period ended September 29, 2017, retirement eligible employees are those employees that either: (1) have attained the age of 60 and completed at least five years of service (which service must be continuous through the date of termination except for a single break in service that does not exceed one year in length) or (2) have attained the age of 65 (without regard to their length of service at L3).

Performance Units. During the quarterly period ended March 31, 2017, the Company granted 33,883 performance units with a weighted average grant date fair value per unit of $168.80. The final payout for these units is based on the achievement of pre-determined EPS goals established by the compensation committee of the Company’s Board of Directors for the three-year period ending December 31, 2019. Units earned can range from zero to 200% of the original number of units awarded, which are converted into shares of L3’s common stock.