How this loan payoff calculator works
This tool simulates your loan one month at a time, the same way your lender's system does. Each month, interest accrues on the remaining balance at your APR divided by 12; your payment first covers that interest, and whatever remains — plus any extra payment — reduces the principal. The loop repeats until the balance reaches zero, giving you an exact payoff date rather than an estimate.
The closed-form version of the same math is the standard amortization formula. If B is your balance, P your total monthly payment, and r the monthly rate (APR ÷ 12 ÷ 100), the number of months to payoff is:
n = −log(1 − r·B / P) / log(1 + r)
When the formula's inner term goes negative, your payment isn't covering the monthly interest — the balance would grow forever. The calculator flags this so you can raise the payment.
Why small extra payments have outsized impact
Interest is charged on the balance, so every dollar of principal you remove today stops generating interest for the entire remaining life of the loan. Early in a loan, most of each payment goes to interest; an extra $100 in month one might eliminate what would otherwise take $150–$180 of scheduled payments to clear years later. That's why the "interest saved" figure in the ledger above is often surprisingly large relative to the extra amount.
Two practical notes. First, confirm with your lender that extra amounts are applied to principal, not held as a prepayment of next month's installment — the wording on the payment form matters. Second, check for prepayment penalties; they're rare on personal loans and US mortgages today, but some auto and international loans still carry them.
Reading the year-by-year table
The table shows, for each year of the payoff, how much you paid in total, how it split between interest and principal, and the balance remaining at year end. Watch how the interest column shrinks each year while the principal column grows — that crossover accelerating is exactly what extra payments buy you.
Frequently asked questions
Does this work for credit cards?
Yes, as a good approximation. Enter your card balance, the APR, and the fixed amount you plan to pay monthly. Card issuers compound daily rather than monthly, so real-world interest will be slightly higher, but the payoff timeline and savings comparison remain accurate enough to plan with.
Should I pay off debt or invest the extra money?
A guaranteed "return" equal to your loan's APR is what early payoff gives you. If your APR is higher than what you'd conservatively expect from investing after tax, payoff usually wins; if the APR is very low, investing may. This is a personal decision that also depends on emergency savings and risk tolerance.
Why is my payoff time "never"?
Your monthly payment is less than or equal to the interest the balance generates each month, so the principal never shrinks. Increase the payment above the monthly interest amount shown in the warning.
Is my data stored anywhere?
No. Every calculation runs in JavaScript on your own device. Nothing you type is sent to a server.