Debt Payoff Calculator
Calculate how many months it will take to pay off a debt balance and the total interest paid, given a fixed monthly payment and interest rate.
Calculator Inputs
Sets the currency this calculator's numbers are denominated in. This is presentation only — it does NOT convert your numbers between currencies, it only changes how they're formatted.
The current outstanding balance to pay off.
The annual interest rate charged on the balance.
The fixed amount you plan to pay each month.
- Months to Debt-Free
- 31.57
- Total Interest Paid
- $1,313.60
- Status
About these results
CalcSpectrum calculators produce automated estimates using established formulas and the specific values you enter. Because real-world outcomes depend on input accuracy, mathematical assumptions, and rounding conventions, please verify critical figures with an appropriately qualified financial, tax, medical, legal, or other professional, as relevant.
Financial Notice: These figures are informational estimates for personal planning only. They do not constitute financial, investment, tax, or legal advice, nor do they represent a lending offer or credit approval. Provider and financial institution figures, rates, fees, and underwriting requirements may differ.
How It's Calculated
Formula
This calculator answers a simple question: if I pay a fixed amount every month toward a debt balance at a given interest rate, how long until it's paid off, and how much interest will I pay in total? It uses the standard closed-form loan-payoff-period formula — the same math behind a loan amortization schedule, solved in reverse for the number of months instead of the payment amount. Each month, interest accrues on the remaining balance at the monthly rate (annual rate / 12), and your fixed payment covers that interest plus reduces the principal. If your payment doesn't exceed the interest accruing each month, the balance never actually shrinks — it stays flat or grows — so that case is flagged explicitly rather than returning a nonsensical result.
Worked Examples
0% APR case: $2,400 balance, $200/month payment
- With no interest, the payoff is pure division: months = 2,400 / 200 = 12
- Total interest paid: $0, since there's no interest rate
Interest-bearing case: $5,000 balance, 18% APR, $200/month payment
- Monthly rate: r = 18 / 1200 = 0.015
- Monthly interest charge on the starting balance: 5,000 × 0.015 = $75 (well below the $200 payment, so the balance will shrink)
- Months to payoff: n = ln(200 / (200 − 75)) / ln(1.015) ≈ 31.57 months
- Total paid: 200 × 31.568 ≈ $6,313.60; total interest: 6,313.60 − 5,000 = $1,313.60
Frequently Asked Questions
What happens if my payment doesn't cover the monthly interest?
The calculation isn't performed, and a clear message explains why: if your fixed payment is less than or equal to the interest accruing on the balance each month, the balance never actually decreases — it either stays flat (interest-only) or grows. Increase the monthly payment above the interest-only threshold to get a payoff timeline.
Why is the result 'months to payoff' a decimal, not a whole number?
The formula computes the exact continuous point at which the balance mathematically reaches zero, which usually falls partway through a month rather than landing exactly on a monthly boundary. In practice, your final real-world payment would typically be a smaller partial amount that brings the balance to exactly zero — this calculator reports the precise underlying figure rather than rounding it in a way that could misrepresent the total interest.
Does this model multiple debts, like a debt snowball or avalanche strategy?
No — this calculator handles a single balance, rate, and payment. For multiple debts paid off in sequence with strategies like the snowball (smallest balance first) or avalanche (highest rate first) method, run each debt through this calculator individually using the payment schedule for that phase of your strategy.
What if my balance is already $0?
Both outputs are $0 and 0 months — there's nothing to pay off, which is the expected boundary case, not an error.