Google sheets: 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:

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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:

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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:


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.