Calculation note
Debt payoff arithmetic is a month-by-month balance ledger. It is useful because the borrower can see how much of a payment survives after interest and fees, and how an extra payment changes both payoff time and total interest.
Debt payoff is a ledger, not a single subtraction
A debt balance usually grows by interest before a payment reduces it. That is why the calculator repeats the same monthly rule instead of simply dividing balance by payment.
The payment must beat interest and fees
If monthly interest and fees are larger than the payment, the balance cannot fall under the entered assumptions. Showing that failure condition is more useful than returning a false payoff date.
Extra payments work by shrinking the next interest charge
An extra payment does not only reduce this month’s balance. It can also lower the interest charged in later months because the future balance is smaller.
Printed payoff records need assumptions attached
Payoff estimates are easy to misunderstand when the rate, payment, extra payment and fee basis disappear. The report keeps those fields beside the result so the plan can be compared with a statement or lender payoff quote.