Perhaps:
An array formula. The values are stored in a range named Data

{SUM(IF(MOD(ROW(INDIRECT("1:"&COUNT(Data)))-1,8)=0,Data,""))}

"Kell2604" wrote:

I need a formula that will sum every x number of cells. For example: I have
data in every 8th cell and I want to write a formula that totals that data.
Is the only way to do that to write my formula =sum(C1...and hold my ctrl key
down while manually selecting each cell...C9,C17,C25) Or can a formula be
written to sum each 8th cell??