I'm doing an amortization.

I have everything working except I want to do a 'payoff' cell....

The payoff will be the sum of payments plus the principal balance.

How can I have this cell update and change as new payments are made?

IE.... if 5 pmts are made, payoff is sum of 5 payments plus the principal
balance.

If 6 pmts are made, its the sum of 6 payments plus the new principal balance.

I only want to count the principal balance if there is a corresponding
payment,
if there is not payment then payoff stops at the last payment made