I don't know if this has already been discussed or not but I couldn't find
anything about it so here's my question:

I am working on a spreadsheet that calculates interest owed based on how
many months have been paid on a contract. The original spreadsheet was based
on a formula that took the date of the last payment and subtracted it from
the current date, then calculated the interest on that period of time. Well,
that doesn't work if the contract is a 2 year contract from 2001 and is
already over. We can't charge more interest than what they were originally
quoted, and we can't charge negative interest either. So I reworked the
formula to use a beginning date and calculate the ending date based on the
number of months in the contract and if the ending date has already lapsed,
to use that date. Otherwise it uses the current date.
I tell you all this to help you understand my problem. This sheet has an
amortization table built in. I want to use that to calculate the interest
already paid based on the months that have been paid on the contract. I can
vlookup the interest for the last payment, but how do I get the sum of that,
plus all previous months, and subtract that from the total finance charge? I
could just do it the way it was done before, but the interest charges were
always anywhere from a few cents to five dollars off. I want this to be dead
on accurate from now on, I don't like guesswork and approximations.