The Company has stock option and equity compensation plans for which a total of 42.3 million shares of the Company’s common stock have been reserved for issuance since the inception of the plans. At September 30, 2018, there were a total of 13.0 million shares available for future grants under the plans.

During the quarter ended September 30, 2018, the Board voted to amend the Amended and Restated 2005 Equity Compensation Plan to increase the number of shares available under the plan from 32.9 million shares to 37.9 million shares, bringing the total number of shares reserved for issuance since inception of all plans from 37.3 million shares at June 30, 2018 to 42.3 million shares at September 30, 2018. The amendment received shareholder approval at the September 20, 2018 annual shareholders' meeting.


				Weighted-average
		Weighted-average		remaining	Aggregate
	Number of	exercise price		contractual term	Intrinsic value
	shares	per share		(in years)	(in thousands)
Outstanding at March 31, 2018	2,456,184	$	13.30

Exercised	(273,009)	$	9.59		$	7,144
Forfeited or canceled	(18,646)	$	19.07
Outstanding at September 30, 2018	2,164,529	$	13.72	4.9	$	75,248
Exercisable at September 30, 2018	1,951,500	$	14.43	4.7	$	66,462

The aggregate intrinsic value at period end represents the total pre-tax intrinsic value (the difference between Acxiom’s closing stock price on the last trading day of the period and the exercise price for each in-the-money option) that would have been received by the option holders had option holders exercised their options on September 30, 2018. This amount changes based upon changes in the fair market value of Acxiom’s common stock.


					Options outstanding							Options exercisable
Range of									Weighted-average	Weighted-average			Weighted-average
exercise price							Options		remaining	exercise price		Options	exercise price
per share							outstanding		contractual life	per share		exercisable	per share
$	0.61	—	$	9.99	478,039	5.4 years	$	1.37	341,363	$	1.35
$	10.00	—	$	19.99	1,043,507	4.1 years	$	14.62	967,154	$	14.39
$	20.00	—	$	24.99	636,293	5.9 years	$	21.31	636,293	$	21.31
$	25.00	—	$	32.85	6,690	5.1 years	$	32.85	6,690	$	32.85
					2,164,529	4.9 years	$	13.72	1,951,500	$	14.43

Total expense related to stock options for the six months ended September 30, 2018 and 2017 was approximately $1.7 million and $2.7 million, respectively. Future expense for these options is expected to be approximately $4.3 million in total over the next three years.


				Weighted-average
		Weighted-average		remaining	Aggregate
	Number	exercise price		contractual term	intrinsic value
	of shares	per share		(in years)	(in thousands)
Outstanding at March 31, 2018	322,823	$	21.42


Forfeited or canceled	(186,090)	$	21.41
Outstanding at September 30, 2018	136,733	$	21.44	1.6	$	3,698
Exercisable at September 30, 2018	—	$	—	—	$	—

Of the performance stock option units outstanding at March 31, 2018, 161,412 reached maturity of the relevant performance period at March 31, 2018. The units attained a 0% attainment level. As a result, they were cancelled in the current fiscal quarter.

Total expense related to performance stock option units for the six months ended September 30, 2018 and 2017 was not material in both periods. Future expense for these performance stock option units is expected to be approximately $0.8 million in total over the next three years.

During the six months ended September 30, 2018, the Company granted time-vesting restricted stock units covering 1,383,409 shares of common stock with a fair value at the date of grant of $40.3 million. Of the restricted stock units granted in the current period, 197,115 vest in equal annual increments over four years, 1,172,263 vest 25% at the one-year anniversary and 75% in equal quarterly increments over the subsequent three years, and 14,031 vest in one year. Grant date fair value of these units is equal to the quoted market price for the shares on the date of grant.


		Weighted-average
		fair value per		Weighted-average
	Number	share at grant		remaining contractual
	of shares	date		term (in years)
Outstanding at March 31, 2018	2,702,497	$	24.60	2.34
Granted	1,383,409	$	29.15
Vested	(745,573)	$	23.94
Forfeited or canceled	(200,222)	$	25.18
Outstanding at September 30, 2018	3,140,111	$	26.73	2.71

During the six months ended September 30, 2018, the Company granted performance-based restricted stock units covering 186,539 shares of common stock having a fair value at the date of grant of $5.8 million, determined using a Monte Carlo simulation model. The units vest subject to attainment of market conditions established by the compensation committee of the board of directors (“compensation committee”) and continuous employment through the vesting date. The 186,539 units may vest in a number of shares from 25% to 200% of the award, based on the total shareholder return of Acxiom common stock compared to total shareholder return of a group of peer companies established by the compensation committee for the period from April 1, 2018 to March 31, 2021.


		Weighted-average
		fair value per		Weighted-average
	Number	share at grant		remaining contractual
	of shares	date		term (in years)
Outstanding at March 31, 2018	561,018	$	25.58	1.67
Granted	186,539	$	31.07


Forfeited or canceled	(110,536)	$	25.08
Outstanding at September 30, 2018	637,021	$	27.28	1.56

Total expense related to restricted stock for the six months ended September 30, 2018 and 2017 was approximately $17.5 million and $14.9 million, respectively. Future expense for restricted stock units is expected to be approximately $20.5 million for the six months ending March 31, 2019, $29.2 million in fiscal 2020, $19.8 million in fiscal 2021, $10.5 million in fiscal 2022, and $1.4 million in fiscal 2023.


		Weighted-average
		fair value per		Weighted-average
	Number	share at grant		remaining contractual
	of shares	date		term (in years)
Outstanding at March 31, 2018	111,111	$	5.33	-
Vested	(45,364)	$	5.33
Forfeited or canceled	(65,747)	$	5.33
Outstanding at September 30, 2018	—	$	—	-

The 111,111 performance-based units outstanding at March 31, 2018 reached maturity of the relevant performance period on March 31, 2018. The units achieved a 100% performance attainment level. However, application of the share price adjustment factor resulted in a 59% reduction in shares vested in the current fiscal quarter.

During the six months ended September 30, 2018, shares having a fair value of approximately $14.6 million were withheld from the units vested and exercised in the tables above. The withheld shares represented the value of employee payroll tax withholding for taxable stock-based compensation awards. The $14.6 million fair value resulted in the return of 496,055 shares to treasury stock and is included in sale of common stock, net of stock acquired for withholding taxes in the condensed consolidated statements of cash flows.

Total share-based compensation expense related to discontinued operations for the six months ended September 30, 2018 and 2017 was $5.7 million and $5.2 million, respectively.

As part of the Company’s acquisition of Arbor in fiscal 2017, $38.3 million of the acquisition consideration otherwise payable with respect to shares of restricted Arbor common stock held by certain key employees was subject to holdback by the Company pursuant to agreements with those employees (each, a “Holdback Agreement”). Total expense related to the Holdback Agreements for the six months ended September 30, 2018 and 2017 was $7.7 million in each period. Through September 30, 2018, the Company had recognized a total of $28.1 million expense related to the Holdback Agreements. Future expense related to the Holdback Agreements is expected to be approximately $10.2 million over the next two fiscal years.

In connection with the fiscal 2018 acquisition of PDP, the Company assumed the outstanding performance compensation plan under the 2018 Equity Compensation Plan of Pacific Data Partners, LLC ("PDP PSU plan"). Total expense related to the PDP PSU plan for the six months ended September 30, 2018 was $7.9 million. Through September 30, 2018, the Company had recognized a total of $9.8 million related to the PDP PSU plan. Future expense is expected to be approximately $7.9 million in fiscal 2019, $15.8 million in fiscal 2020, $15.8 million in fiscal 2021, and $15.7 million in fiscal 2022, based on expectations of full attainment. At March 31, 2018, the recognized, but unpaid, portion balance related to the PDP PSU plan in other accrued expenses in the condensed consolidated balance sheet was $8.9 million.