=SUM(M13:M16)/(WEEKNUM(TODAY())-17)
The 17 needs to be adjusted the first time you use it to make sure you get
your 3 divisor.

Or, you could just type the 3 in a helper cell, say A1, and then you would
just change it weekly instead of having to modify the formula(s)
=SUM(M13:M16)/A1

Vaya con Dios,
Chuck, CABGx3






"Donnas" wrote:

This may be really stupid questions but here it goes...
Below is my formula, I am adding some columns then dividing by 3. Next
week I will need the same columns added but will need to divide by 4, the
follwing week by 5. Is there any way Excel will do this without me manually
changing the number each week?

=SUM(M13:M16)/3