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Not certain what you are doing but see the calculation below for rolling sum
this will give you an R12 - you need to put in the limits - your calculation for last month is not correct it should be dateadd('month',-1,[Order Date]) but I don't know where or if you would use it
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Find my approach as reference below and stored in attached workbook version 10.5 located in the original thread.
1. "Proof of the Pudding";)
2. Define Custom Date NM D1. Order Date (Month/Year)
3. NM M1. Sales LTM: window_sum(sum([Sales Target]),-11,0)
//calculate the sum over the last 11 month & current month for each month
4. Drag the required objects to the indicated locations
5. NM M1 Sales LTM > Right Click > Text menu > Compute using > NM D1. Order Date (Month/Year)
Forum - Rolling LTM_nalmai_10.5.twbx 707.3 KB
Thanks! Saw this now.
WINDOW_SUM is what I need - not sure how I could miss that.
Perfect, thanks again, Jim.
Glad to help out