SSRS - Aggregate LAST YTD or LAST CHILD Value in an SSAS query

Trying to aggregate an aggregate is not possible in SSRS. You can write custom code to capture the running total of values in a report, which works, but can have unexpected behaviour when groups in your report change. It also prevents you from using some other SSRS functionality, for example repeating column headers on a page.

Here is an example of a solution that works using math, which doesn't prohibit you from using any functionality, since SSRS has no trouble aggregating math equations. This solution has many applications in filtering out unwanted values in a row. I will show you an example where only the most recent (LAST) value of YTD is wanted for each group of rows in a query.