Problems with Pivot table

Hi,

I have been searching for ages for a resolution to this issue. I want to insert a calculated field into a PT that adds up dollar margin that has been sorted highest to lowest, to give a cumulative % of the total margin in the table. I have tried everything, including adding an outside helper column however this is not working.

I want to be able to have it so that regardless of how the data is sorted, the cumulative column starts with the first cell in the table, & adds the values as it goes down. For example total margin in the attached example is $285 out of $563 total, so it shows 50.6% as the percentage of total margin. The formula would then add the next line of sorted margin to the cumulative total and express as a percentage. In this example it would be $285 + $241 = $526, which as a cumulative percentage of total is 92.8%.

I really need to have it as a calculated field as I want to be able to manipulate the data and dependent upon the field the data is sorted on, need to have a progressive margin % that can be conditionally formatted.

The attached example is in Excel 2007.

Any help would be appreciated.