Have you tried the formula DIBO posted? Just put this in a cell somewhere and change the 'A:A' and 'B:B' references to reflect the column letters of the relevant ones in your spreadsheet containing dates and weekly amounts. It should always calculate a total based on the last 365 days.
Just a thought, but you can also do something like this (based on the same two column approach and assuming that you've got an entry for every week):
Put this formula in the third column at the end: =SUM(OFFSET(B53, -51,0):B53)
If the cell you're putting this in is say on the 65th row, change B53 to B65 (both instances). You can copy this formula down to the rows below and it should give you a total for the last 52 rows. If there are less than 52 rows in your sheet, it will give you an error message as the result. If you're getting an error message when entering the formula, check if you're using a system set up to use a comma as a decimal separator. If that is the case, you will need to use semicolons instead of commas in the formulas.
Last edited by Jhieminga; 4th Jun 2018 at 14:29.
Reason: added information