Simplified, I have a table with 2 time dimension fields: Subscription Month and Cancellation Month, plus two values, Amount and Cancellation Amount - please see below and attached. I want to calculate in MDX Amount minus Cancellation Amount where Subscription Month=Cancellation Month and be able to filter the formula on other dimensions, not involved in this formula, such as Client. I have tried AGGREGATE Cancellation Amount by Cancellation Month but when filtered by Subscription Month in pivot, it gives incorrect results.