A question you mentioned B2 to B298 but in your equation you use column C?
and mod of row 22 with 12 basis is 10

try instead

=SUM(IF(MOD(ROW(C22:C298),12)=10,C22:C298,""))
entered as an array (Control/Shift enter)

I was surprise that the sumproduct function would not work with the
correction to the mod section. but it didn't

Hi
In B301 I need a formula that will add the contents of every 12th cell
starting at b22 and ending at b298. I am unsucessfully using
=SUMPRODUCT(C22:C296,--(MOD(ROW(C22:C296),12)+1=1))
What am I doing wrong?
Thanks!