Interesting problem on accumulation of sum

[#1]

I have a data set that contains begin and termination dates I want to sum the column seatcount within.

This is some representative data:

BeginDate     TermDate     SeatCount

12/1/2008	3/31/2009	2
7/16/2014	1
10/23/2012	12/31/2012	0
6/10/2008	7
3/18/2013	10
1/1/2001	3/1/2010	10
8/13/2013	3/31/2014	10
6/26/2014	3
3/1/2008	6
12/4/2013	1
8/7/2013	2
11/7/2013	1

What I have then is a pivot table with a single dimension MonthEnd(BeginDate). The expression i want is based on the following:

sum(if(TermDate<=BeginDate, 0, SeatCount)).DateDate

=MonthEnd(BeginDate)	sum(if(TermDate<=BeginDate, 0, SeatCount))
8/31/2014	10
7/31/2014	293
6/30/2014	231
5/31/2014	215
4/30/2014	354
3/31/2014	321
2/28/2014	158
1/31/2014	296
12/31/2013	157
11/30/2013	203
10/31/2013	151
9/30/2013	270
8/31/2013	148
7/31/2013	188
6/30/2013	188
5/31/2013	186
4/30/2013	264
3/31/2013	178

What I want is the accumulated seatcount minus the seatcount that is terminated. My thought is I should be getting a number that is increasing by date, but that is not happening. Is this a recursion issue?