Pivot tables - calculated fields, cumulative of another field

[astrbac]

Hello all,

I am having what seems to be a trivial issue - how to add a calculated field to an Excel pivot table, a field which keeps the running total (or cumulative) based on some other field?

Example:

----
Total plan: 400
days: 4
----

Day 1. Daily plan: 100; Cost: 90; Running total (cost): 90;
Day 2. Daily plan: 100; Cost: 80; Running total (cost): 90 + 80 = 170
Day 3. Daily plan: 100; Cost: 90; Running total (cost): 170 + 90 = 260
Day 4. Daily plan: 100; Cost: 110; Running total (cost): 260 + 110 = 370


[TABLE="width: 500"]
<tbody>[TR]
[TD]Day[/TD]
[TD]Daily plan[/TD]
[TD]Daily cost[/TD]
[TD]Cumulative cost[/TD]
[TD]Cumulative remaining[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]100[/TD]
[TD]90[/TD]
[TD]90[/TD]
[TD]310 (400-90)[/TD]
[/TR]
[TR]
[TD]2[/TD]
[TD]100[/TD]
[TD]80[/TD]
[TD]170[/TD]
[TD]230 (400-170)[/TD]
[/TR]
[TR]
[TD]3[/TD]
[TD]100[/TD]
[TD]90[/TD]
[TD]260[/TD]
[TD]140 (400-260)[/TD]
[/TR]
[TR]
[TD]4[/TD]
[TD]100[/TD]
[TD]110[/TD]
[TD]370[/TD]
[TD]30 (400-370)[/TD]
[/TR]
</tbody>[/TABLE]


I need to be able to track and predict budget expenditure and adjust on a daily basis so that on the last day all the budget gets spent.

many thanks for all replies!