Aggregated column based on a pivot table column

Question

My data set consists of items along with a date attached to each one. I created a pivot table that shows the count items per each year, like this:

Year        Count
1976        1
1978        1
1983        1
1984        2
1992        2
2000        1
2002        2
2003        8
2004        2
2005        2

I'd like to add another value to the pivot table that shows the aggregate count up to and including that year, so:

Year        Count         Aggregate
1976        1             1
1978        1             2
1983        1             3
1984        2             5
1992        2             7
2000        1             8
2002        2            10
2003        8            18
2004        2            20
2005        2            22

Any tips?