variable moving average periods

You have to do the math with the ROW function.
ROW() returns the row number that the function is entered in.
So if you put that formula in H18, then ROW() = 18
Your formula changes from
=(AVERAGEIF(INDEX(G$8:G$2500,ROW()-$H$3-1):INDEX(G$8:G$2500,ROW()),"<>0")
to
=(AVERAGEIF(INDEX(G$8:G$2500,18-$H$3-1):INDEX(G$8:G$2500,18),"<>0")

H3 is 2 you said
=(AVERAGEIF(INDEX(G$8:G$2500,18-$H$3-1):INDEX(G$8:G$2500,18),"<>0")
changes to
=(AVERAGEIF(INDEX(G$8:G$2500,18-2-1):INDEX(G$8:G$2500,18),"<>0")
becomes
=(AVERAGEIF(INDEX(G$8:G$2500,15):INDEX(G$8:G$2500,18),"<>0")

Now, that 15 is NOT a row number.
It's an INDEX number, relative to the range G8:G2500
15 means the 15th cell in G8:G2500
That is G22

=(AVERAGEIF(G22:INDEX(G$8:G$2500,18),"<>0")

The 18th cell in G8:G2500 is G25
=(AVERAGEIF(G22:G25,"<>0")


So your formula, in H18 while H3 = 2 is averaging G22:G25

Hi Jonmo, thanks. I was playing around with the wrong number. I appreciate your help!

You're welcome.