Debt Payoff CalculatorFree online financial calculator — instant results, no sign-up
Months and interest to clear a debt, with extra payments.
Estimates only, based on the inputs and assumptions shown. This is not financial, investment, tax, or legal advice. Prices, rates and local rules may change; crypto scenarios do not predict returns. Confirm important decisions with a qualified professional.
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About the Debt Payoff Calculator
This calculator determines how many months it will take to pay off a debt with your current monthly payment compared to an accelerated payment that includes an extra monthly amount. It also calculates the total interest saved by applying that extra payment. Borrowers managing credit cards, personal loans, or auto loans use it to evaluate debt acceleration strategies.
- Balance
- The outstanding principal balance on the debt, entered in dollars (sensible range: $100 to $1,000,000).
- Rate
- The annual percentage rate (APR) charged on the debt, entered as a percentage (sensible range: 0.1% to 40%).
- Monthly payment
- The base amount paid each month toward the balance, in dollars (must exceed monthly accrued interest).
- Extra
- Additional amount paid each month on top of the regular monthly payment, entered in dollars (default is $100).
Formula and method
n = -ln(1 - (P × r) / PMT) / ln(1 + r) Interest Saved = (PMT_reg × n_reg) - (PMT_extra × n_extra)
- nNumber of monthly repayment periods (calculated as n_reg for regular payment and n_extra with extra payment)
- PCurrent debt balance
- rMonthly interest rate, equal to annual rate divided by 1,200
- PMTMonthly payment amount (PMT_reg is regular payment; PMT_extra is regular payment plus extra amount)
The tool computes the number of periods (nper) using standard logarithmic loan amortization formulas for both the baseline payment and the augmented payment. Total costs for each schedule are calculated by multiplying each monthly payment amount by its respective duration, and the difference yields interest saved. Payoff months are rounded to one decimal place, and interest saved is formatted to two decimal places.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Balance15000 $
- Rate12 %
- Monthly payment400 $
- Extra100 $
Results
- Months (regular)47.2
- Months (with extra)35.8
- Interest saved$971.22
How to use the Debt Payoff Calculator
- 1Convert the annual percentage rate to a monthly decimal interest rate by dividing by 1,200.
- 2Calculate baseline payoff duration (Months regular) using the balance, monthly interest rate, and base payment.
- 3Calculate accelerated payoff duration (Months with extra) using the base payment plus the extra monthly payment.
- 4Multiply each duration by its corresponding total monthly payment and subtract the accelerated total from the baseline total to find interest saved.
Reading your result
Comparing regular months to months with extra shows the reduction in repayment time achieved by the extra contribution. Interest saved reflects the cumulative dollar savings resulting from reducing the principal faster and minimizing accrued compound interest. If regular monthly payment does not cover monthly interest, the calculation cannot resolve to a payoff time.
Limitations
The calculation assumes a constant annual interest rate and an unchanging extra payment each month until zero balance is reached. It does not account for variable APRs, introductory promotional rates, prepayment penalties, annual fees, or compounding intervals other than standard monthly compounding.
Common questions
What happens if my monthly payment is smaller than the monthly interest?+
If your payment is less than or equal to the balance multiplied by the monthly interest rate, the principal balance will never decrease, leading to negative amortization where the debt is never paid off.
Does this calculator apply the extra payment directly to the principal?+
Yes, standard loan mathematics assumes that any amount paid beyond the scheduled interest goes directly toward reducing the outstanding principal balance.
Why is the final payoff time reported with a decimal fraction of a month?+
The formula solves for exact fractional repayment cycles; in practice, the final month requires a smaller, partial payment rather than a full payment.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.