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

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.

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)`.