Debt Payoff Calculator
See how long it takes to pay off a debt, the total interest, and how much an extra monthly payment saves.
How it works
Months = log(payment ÷ (payment − balance × r)) ÷ log(1 + r), where r = APR ÷ 12
Each month, interest is charged on the remaining balance and your payment covers that first; whatever is left reduces the balance. If the payment barely exceeds the monthly interest, payoff drags on for years. An extra payment goes straight to principal, so it shortens the term and cuts total interest — and the effect is largest early, when the balance is highest.
Worked example
An $8,000 balance at 22% APR paid at $250 a month takes about 49 months and roughly $4,160 in interest. Adding $100 (to $350 a month) clears it in about 30 months and $2,463 interest — saving around $1,695 and 19 months.
Frequently asked questions
Why do small extra payments help so much?
Extra money goes entirely to principal, which lowers every future interest charge. On high-APR debt this compounds into large savings and a much shorter payoff.
Snowball or avalanche across several debts?
Avalanche (highest APR first) saves the most interest mathematically. Snowball (smallest balance first) delivers quick wins that keep you motivated. The best is the one you will stick with.
What if my payment barely covers the interest?
The balance shrinks painfully slowly and payoff can take decades. Any amount above the monthly interest is what actually reduces the debt — raise it if you can.
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This is an educational estimate, not financial advice. Confirm figures with your lender, advisor or tax professional.