How to create a grouped per-30-day total without filling thousands of cells?

Question

I have a Google Spreadsheet that counts a number of events that happened per day. This is what it currently looks like:

I would like to have a 30-day total running alongside, i.e., the total events for every 30 days. It would look something like this:

Here, U7 consists of the sum of the first 30 events (T7:T36), U8 is the sum of the next 30 (T37:T66), U9 sums the next 30 and so on.

I can quite easily do this by filling all of the cells in column U with:

=SUM(OFFSET($T$7,30*(ROW()-7),0,30,1))

but this means every cell has to be filled and it is a bit slow in the scheme of this spreadsheet, particularly as I will need numerous columns like this. Is there a way to do this with a single filter in the top cell or something of the sort? I haven't been able to figure out a way to do that.

Answer 1

I think on U7 you can use =SUM(T7:T36), then drag the formula all the way down, or copy/paste it down. On U8 it should automatically change the formula to =SUM(T8:T37).

Another suggestion to improve the sheet would be to add another column for days, and keep S column as dates only (so remove the Sunday). Then you can do conditional formatting to highlight the entire row for all Sundays with the new column for days.