Trailing 12 Months (TTM) Formula For Sales Sheet

Hello Everyone,

I have a sales sheet where I am tracking sales for 3 different businesses.

I wanted a Trailing Twelve Month (TTM) formula where it can add the latest sales of the past month for all 3 businesses and give me an average sales figure. This will help me in seeing a trend whether the sales is increasing or decreasing or remaining somewhat constant.

I would also like it to be updated continuously. For e.g. if I add October sales then it should ignore October of last year and calculate average sales from last November to this year's October thereby taking into consideration the new TTM for this year.

I am attaching a false sales sheet so that the person helping can get sales figures and help me out with the help of it.

I thank everyone who has come to my thread with the intention of helping regardless of him able to help or not