Calculating Yearly Average by current month

I need to create a SS that calculates the yearly average from January until the end of the previous month.


Excel example.JPG

Currently I have =SUM(A2:G2)/12 and each month I go in an change the range, but I would like it to update each month to include the month that just finished.
Any help would be appreciated.

thanks! This got rid of the #VALUE error I was getting, but I don't think it's calculating correctly. The average should be 929 but the result of that formula is 125

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TOTAL Monthly Avg.
0 0 1500 0 2500 2500 0 2200 2000 900 600 600 12800 CY Actuals 125

I'm confused
The sum of Jan:July is 6200. If you're dividing by 7 (number of months summed) the result is 886, if you're dividing by 12 the result is 517 (what the formula returns when I try in my worksheet). Where would 929 come from?