Schedule II VALUATION AND QUALIFYING ACCOUNTS

12 Months Ended

Dec. 31, 2017

Schedule II VALUATION AND QUALIFYING ACCOUNTS

Schedule II VALUATION AND QUALIFYING ACCOUNTS

Schedule II
COGENT COMMUNICATIONS HOLDINGS, INC. AND SUBSIDIARIES
VALUATION AND QUALIFYING ACCOUNTS
(in thousands)

Description	Balance at Beginning of Period		Charged to Costs and Expenses		(Deductions)			Balance at End of Period
Allowance for doubtful service accounts receivable (deducted from accounts receivable)(a)
Year ended December 31, 2015	$	1,707	$	4,746	$	(4,696	)	$	1,757
Year ended December 31, 2016	$	1,757	$	3,840	$	(3,863	)	$	1,734
Year ended December 31, 2017	$	1,734	$	4,835	$	(5,070	)	$	1,499
Deferred tax valuation allowance
Year ended December 31, 2015	$	245,104	$	1,058	$	(132,770	)	$	113,392
Year ended December 31, 2016	$	113,392	$	3,102	$	(6,300	)	$	110,194
Year ended December 31, 2017	$	110,194	$	20,102	$	(623	)	$	129,673

(a)         Bad debt expense, net of recoveries, was approximately $3.7 million for the year ended December 31, 2017, $2.8 million for the year ended December 31, 2016 and $3.3 million for the year ended December 31, 2015.