The program automatically adds the interest portion of missed blended payment to the balance. The principal portion of the blended payment must be paid back in addition to the interest. The number you type in the prepayment column is normally subtracted from the balance. If the prepayment column number is a negative number, it is added to the balance. Obviously the principal portion of the blended payment must be paid back in addition to the interest. This simple procedure can be repeated anywhere on the schedule for other missed payments in order to keep your amortization schedule intact and accurate so that there are no misunderstandings down the road as to the balance owing. What could be simpler?

It is also interesting to note, if this was the only missed payment and the mortgage was continued at the same interest rate to the end of the amortization period, the result of that missed payment is $10,000 plus in additional interest costs (subtracting the before and after SPREADSHEET Int. = values).