Debt Payoff Calculator
Solving for Time Instead of Payment
Most loan calculators start with a term and solve for the payment. This one flips the question: given a balance, an interest rate, and a fixed payment you're already able to make, how long will it actually take to reach zero? That requires solving the amortization formula for the number of periods rather than the payment amount, using logarithms.
The Formula
n is the number of months to pay off the debt, r is the monthly interest rate, P is the current balance, and M is the fixed monthly payment. If the payment doesn't exceed the first month's interest charge, this equation has no valid solution — the debt would never be paid off, and the calculator flags that case directly.
Where This Is Useful
- Personal loans and fixed debts — seeing the real payoff timeline for a debt you're paying down at a set monthly amount.
- "What if I pay more?" scenarios — testing how a higher fixed payment shortens the payoff timeline and cuts total interest.
- Setting a realistic debt-free date — converting a payment plan into an actual month count rather than an open-ended guess.
$8,000 Balance at 19.99% APR — Payment Speed
| Monthly Payment | Time to Pay Off | Total Interest |
|---|---|---|
| $150 | 132.75 months (11y 1m) | $11,913.01 |
| $200 | 66.44 months (5y 6m) | $5,287.40 |
| $300 | 35.55 months (3y 0m) | $2,666.12 |
At a payment of $150, total interest actually exceeds the original balance — a reminder of how much high-APR debt costs when paid down slowly.
How to Use This Calculator
- Enter the Current Debt Balance.
- Enter the Annual Interest Rate.
- Enter the Monthly Payment you plan to make.
- Select Calculate to see the time to pay off and total interest paid.
Related Calculations
Paying off a credit card specifically? See the Credit Card Payoff Calculator, or evaluate combining several balances with the Debt Consolidation Calculator.