On Nov 7, 7:17*am, martinbarnes
wrote:
i'm trying to set up a formula that calculates
interest over a period, based on a compounding
interest rate... any ideas

Click on Help Excel Help and enter "compound interest", and you
should get lots of ideas.

If you are still stumped, post a follow-up with a specific example.

Suppose you deposit $1000 into an account that earns 3% interest
compounded daily. After a typical year, the account balance will be:

=round(fv(3%/365, 365, 0, -1000), 2)

If you want just the interest:

=round(fv(3%/365, 365, 0, -1000), 2) - 1000

HTH.