optimize this redundancy in the cell function

I want the average gain in a column without writing it by hand.

this is the reiteration I want to optimize —> [ =AVERAGE(B3-B2;B4-B3;B5-B4) ]

what I need to do is take the value of the day subtract the value of the day before and do the avarage of that for every day in a month.

with what I have done, I need to click every cell by hand but I’m lazy and also want to improve that for sake of optimization.

how should I do that?

thanks and sorry for any mistakes in my english.