Teethless Mama, your formula worked for most part but I am getting DIV/0
error on worksheets with no data. Please advise

I am trying to get an average of time spent each month on an activity. The
spreadsheet has 12 months and only 3 of the months are populated.I think it
is still counting months 4-12 in my average. As each months time is entered
I
want it to recalculate the average.
"Teethless mama" wrote:

Try this elegant formula:

=AVERAGE(IF(($M$88:$AT$880)*(MOD(COLUMN($M$88:$AT $88),3)=1),$M$88:$AT$88))

ctrl+shift+enter, not just enter