=SUMPRODUCT(A3:A13,--(MOD(ROW(A3:A13),3)=0))

--

HTH

RP
(remove nothere from the email address if mailing direct)


"Jim Brass" wrote in message
...
If you have a column of numbers and want to add every third one, what
formula do you use?
I tried stuff like
=SUMIF(A3:A13,MOD(ROW(),3)=0) as an array formula

My mind is drawing a blank. Thanks Jim