On Jun 6, 6:04 pm, Amanda wrote:
hi,

I need a formula which will add together the total number of units (shown
monthly) and for every 90th unit put a cost of £250.

So, for example:

Month 1 2 3 4 5
Units 45 46 15 76 22
Cost £0 £250 £0 £250 £0

How can I do this without it showing £250 in every month???

Thanks

Amanda

Amanda,
in your example the 250 cost appears every 60, not every 90 days, i.e.
every two months.

=SUMPRODUCT(B2:F2+250*(MOD(B1:F1,2)=0))

My formula uses MOD(...,2) for every two months. Change to 3 if you
mean every 3 months.

HTH
Kostis Vezerides