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Debt Payoff Calculator: Payoff Time, Interest and Extra Payments

A debt payoff calculator estimates how long a balance will take to repay when interest is charged monthly and you make a fixed payment. It helps test how extra payments change the timeline and interest cost.

Updated 2026-07-09Reviewed by US Finance Hub Editorial TeamCalculations run in your browser

Quick answer

Your payment must exceed the monthly interest charge for the balance to decline. Increasing a fixed payment usually reduces both payoff time and total interest.

At a glance

What it calculates
Estimate payoff time and interest for a debt balance using a fixed monthly payment and optional extra payment.
Who it is for
US borrowers prioritising card, personal-loan and auto balances in a payoff plan.
Coverage
United States (federal rules; state and local rules vary)
Data and assumptions
One balance and APR at a time with a fixed monthly payment, no new borrowing and no fees.
Cost
Free, no signup, calculations run in your browser
Last reviewed
2026-07-09

Calculator

Enter your numbers

Current balance to repay.
Annual interest rate.
Regular amount paid each month.
Additional recurring payment.

How to use this calculator

  1. Enter the current balance and annual rate.
  2. Enter the regular monthly payment.
  3. Add an optional recurring extra payment.
  4. Review payoff time and interest.
  5. Confirm how your creditor applies extra payments.

Explanation

What it is

A debt payoff calculator estimates how long a balance will take to repay when interest is charged monthly and you make a fixed payment. It helps test how extra payments change the timeline and interest cost.

How it works

The calculator applies one month of interest to the outstanding balance, subtracts the entered fixed payment, and repeats until the balance is repaid.

When to use it

Use it when you have several balances and need to decide the payment level and payoff order before committing to a plan.

Limitations

  • Each balance is modelled separately with a fixed payment and one APR.
  • Variable rates, deferred interest and balance transfer fees are excluded.
  • Collections, settlements and hardship arrangements change the outcome.

Key terms

Principal
The balance before future interest.
Payoff period
The number of payments needed to reduce the balance to zero.
Avalanche method
Directing extra money to the highest-rate debt while paying minimums on others.
Snowball method
Directing extra money to the smallest balance while paying minimums on others.

Formula

The calculator applies one month of interest to the outstanding balance, subtracts the entered fixed payment, and repeats until the balance is repaid.

Each month: new balance = old balance + interest − payment

Worked example

For a $20,000 balance at 18%, paying $700 instead of $600 per month shortens the payoff period and reduces the amount exposed to interest.

FAQ

How long will it take to pay off my debt?

Enter the balance, rate, and fixed payment. The payment must be higher than the monthly interest for the debt to amortize.

Should I use the debt snowball or avalanche?

The avalanche often minimizes interest; the snowball can provide earlier account closures. The best method is one you can sustain.

How much difference does an extra $100 make?

It depends on balance and rate. Extra principal reduces the balance that generates future interest, so high-rate debt can show a large benefit.

Should I pay debt or build an emergency fund first?

Many people keep a basic cash buffer while paying high-cost debt, but the right balance depends on job stability, rates, minimums, and access to cash.

Does this include late fees or variable rates?

No. Add changing rates, fees, and new borrowing separately when evaluating a real account.

Common mistakes

  • Letting the payment fall as balances shrink instead of rolling it forward.
  • Consolidating into a longer term and paying more interest overall.
  • Leaving the paid-off card open and rebuilding a balance on it.
  • Ignoring an emergency buffer, which forces new borrowing mid-plan.

Tips

  • Pay the highest APR first to minimise interest; pay the smallest balance first if you need early wins.
  • Keep total payments constant as balances clear so the freed payment rolls to the next debt.
  • Direct windfalls and tax refunds to the highest-cost balance.
  • Re-run the plan whenever a rate or minimum payment changes.

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Sources and editorial review

Educational estimates only; not personalized financial, tax, legal, lending, investment, or insurance advice.