Each sheet references a month and are titled as followed January '21, February '21 etc.

Within each of these sheets I collect scores gathered on a certain date. Column C contains date that result was collected and Column D contains result.

I have collected overall average of results using =IFERROR(AVERAGE('March ''21:May "21'!D4:D18),"")

But as I add a sheet for each month I'd like to review a rolling 90 day average so it is relevant for result analysis.

I've used an average of averageifs for each page but that only gives me an average of averages. It doesnt average the scores themselves.

I also tried using =AVERAGEIFS('March ''21:May ''21'!D4:D18,'March ''21:May ''21'!C4:C18,">"&TODAY()-90,'March ''21:May ''21'!C4:C18,"<"&TODAY()) but this was not successful.

Any help would be greatly appreciated.

Each row represents a person that I've collected the result for and my end game would be to be able to calculate rolling averages for each person too