How to calculate debt payoff
n = −log(1 − rB ÷ P) ÷ log(1 + r)
Worked example. Debt-free in: 48 months.
Example inputs — Debt balance: $15,000; Interest rate (APR): 12%; Monthly payment: $400. Starting values are illustrative.
4 yrs 0 mos
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
Each month interest is added to your balance and your payment is subtracted. We repeat until the balance reaches zero.
Using the debt payoff estimate
This calculator asks how long a balance takes to clear when you make the same payment every month. It applies monthly interest and then reduces the balance by the payment, assuming no new borrowing. The payoff period and interest total show what your payment habit can achieve under a fixed rate. For several debts, work through each balance separately or use a multi-debt strategy tool rather than treating different rates as one exact loan.
Step-by-step inputs
- Debt balance. Enter the outstanding debt being modeled. Do not add future interest to the balance; the calculator generates that interest during repayment. Starting example: $15,000 .
- Interest rate (APR). Use the annual rate for this debt. Monthly interest is approximated using one-twelfth of that percentage. Starting example: 12% .
- Monthly payment. Enter the full fixed monthly payment toward this balance. It needs to exceed the initial monthly interest charge for the balance to shrink. Starting example: $400 .
Worked example with the starting values
Using the starting inputs, the estimate is Debt-free in: 48 months.
Each modeled payment first covers that month's interest and then reduces principal. The final payment can be smaller than the regular amount, so total paid is not necessarily the displayed month count multiplied by the regular payment. The interest total is the cost above the original balance.
4 yrs 0 mos
- Total interest
- $3,894
- Total paid
- $18,894
Compare monthly payment scenarios
All other inputs stay at their starting values. These are modeled comparisons, not quotes, predictions or individual recommendations.
| Monthly payment | Debt-free in |
|---|---|
| $300 | 70 months |
| $400 | 48 months |
| $500 | 36 months |
Make a useful comparison
Compare payment amounts at the same rate and balance. A higher sustainable payment can cut both the timeline and total interest, especially when the original payment barely exceeds the monthly interest charge. Use your take-home budget to choose an amount you can repeat.
Separate old-debt repayment from new purchases. Continuing to add charges means the balance may not follow this estimate even when every scheduled payment is made. A payoff plan needs an explicit way to fund current spending without rebuilding the debt.
Review the result whenever the rate or payment changes. Variable-rate debt, promotional-rate expirations and irregular extra payments change the trajectory. A new calculation from the latest balance is more useful than expecting the original date to remain exact.
Common mistakes to avoid
- Paying only the month's interest leaves principal unchanged. Paying less can increase the balance, so there may be no finite payoff date under that scenario.
- The model does not include late fees, penalty rates or lender-specific minimum-payment rules. A statement's minimum can change as the balance changes.
- Do not assume all debt should receive the same extra payment. Required minimums, rates, penalties and available cash all matter when allocating money across several accounts.
Assumptions & limitations
- Fixed rate and on-time payments.
- Excludes origination fees, late fees and penalties unless entered.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
Which is better: debt snowball or debt avalanche?
Avalanche directs extra money to the highest interest rate while keeping minimum payments on the others; under comparable fixed terms it generally minimizes interest. Snowball targets the smallest balance first for quicker account closures. This single-debt tool models neither ordering; use the debt snowball comparison tool for multiple balances.
Can you combine the snowball and avalanche methods?
Yes. You might clear a small balance first, then prioritize the highest rate. Keep all required payments current. A hybrid's interest cost depends on the balances, rates and how extra payments are reassigned.
How fast can you pay off $30,000 in debt?
There is no single timeline without a rate and payment. For one balance at 12% APR with $800 monthly and no new borrowing, Debt-free in: 48 months. Change those inputs to match your debt.
How long does it take to pay off $10,000 in credit card debt?
At an illustrative 20% APR and $400 monthly with no fees or new purchases, Debt-free in: 33 months. A card's daily interest calculation can differ.
Should I use savings to pay off credit card debt?
Compare the card's interest cost with the need to retain cash for essential bills and emergencies. Emptying savings can force new borrowing. Consider promotional rates, income stability and other obligations before making a lump-sum payment.
Does paying off credit card debt improve your credit score?
Reducing reported revolving balances may improve utilization, but scores depend on several factors and reporting dates. This calculator cannot predict a score change; paying off debt does not erase prior late payments.
What is the best way to pay off debt?
List balances, APRs and minimum payments, keep required payments current and choose an extra payment your budget can sustain. Compare highest-rate-first and smallest-balance-first plans. If payments are unaffordable, speak with the creditor or a reputable nonprofit credit counselor.
Why is the final payment different?
Only the remaining principal and modeled interest need to be cleared. The engine can stop with a smaller last payment rather than charging a full extra installment.
What happens if I keep borrowing?
The estimate no longer describes the balance path. It assumes no new charges or borrowing throughout repayment.