If the monthly extra payment is fixed (ie always happens for the same amount
every month), then the term will decrease. Simply calculate the new term using
NPER, then feed this value to Cumipmt.

If the extra payments are irregular, but few in number, you could recalculate
the new loan parameters each time, then use Cumimpt. For example, if someone
paid an extra $1000 47 months into a loan, calculate the FV after 47 payments,
subtract the $1000, then calculate the new term using NPER, and feed this to
Cumipmt.

If irregular payments happen a lot, you're better off building an amortization
table.

--
Regards,
Fred


"Mortgage Man" wrote in message
...
I am looking for a way to find the total interest paid on a loan, if the
borrower decides to make a fixed extra monthly payment toward principal. The
cumipmt function does not allow me to put in a pmt. Is there another way to
do this?

Thanks in advance