I'm creating a debt payoff sheet, paying off multiple monthly payments. I
want to roll one payment into the next when amount reaches zero. For
example. I have one payment of $300.00 per month a minimum monthly payment
of $250 per month for 3 months. I also have a $600 payment per month for 6
months. When that three month payment is over, I want to roll the 300.00
onto the $600 payment to get to $900.00

Right now, i'm manually doing the additions for when a debt amount due is
greater than zero. I'd like formula that is an if then, for example if the
amount due is greater than 0, then subtrack the payment amount, unless the
payment amount is greater than amount due, then only apply the total amount
due. Any suggestions?