Need help determining # of invoices

[Guest]

Hello,

I am trying to create a spreadsheet that will determine the # of invoices
for a contract that will happen in 2005. Primarily will be, how many invoices
will happen in quarterly installments. This is easy if you have say a 12
month contract starting in January. There will be 4 invoices, an invoice
occuring on Jan, April, July and October. But now say the contract starts in
April and it is a 7 month contract. An invoice will occur in April, July and
October. So only 3 invoices will occur. Is there any way to set this up in
Excel to automatically calculate this? Hope this makes sense.

 

[Bob Tarburton]

This should get you close
If A1 is date the contract starts and A2 the date it ends
=ROUNDUP((MONTH(A2)-MONTH(A1))/3,0)+1

Shortcoming is if start date is early in the month and end
date is late in that month, you might get slightly more
than 90 days between billings. Need a more indepth formula
that includes days if you're worried about getting an
early June bill out for a job that starts early March and
ends late June, for example.