Debt calculator
Debt Payoff Calculator
Estimate payoff time, total interest, and how much faster an extra monthly payment could move your plan. Runs in your browser — no sign-up, no data collected.
How this calculator works
The calculator compounds interest monthly using the APR you enter, then subtracts your monthly payment until the balance reaches zero. It is a simplified model designed for learning and planning, not for matching your lender's statement to the penny.
The formula, step by step
For each month, the tool runs three steps:
- Add interest:
monthly interest = current balance × APR / 12 - Subtract payment:
new balance = current balance + monthly interest − (monthly payment + extra payment) - Repeat until the balance reaches zero, counting the months as it goes.
The total of all interest added is your estimated interest. The payoff month count becomes your estimated payoff time. Total paid is the sum of every payment that actually reduced your balance.
Worked example: a credit card balance
Suppose you owe $8,500 at 21.99% APR and pay $325 a month. Month one works like this:
- Interest:
$8,500 × 0.2199 / 12 = $155.85 - New balance:
$8,500 + $155.85 − $325 = $8,330.85
Each following month the balance is a little smaller, so the interest charge shrinks and more of your $325 goes to principal. Add $100 extra a month and that shrink speeds up considerably — you finish sooner and pay far less interest overall. Try it in the tool above and watch the "Estimated interest" number drop.
Why extra payments matter so much
Because interest is calculated on the remaining balance, every extra dollar you pay does two jobs: it removes a dollar of principal and it removes the interest that dollar would have generated for the rest of the loan. This is why even a modest extra payment — $50 or $100 a month — can cut many months off a payoff timeline and save hundreds in interest. Use the extra-payment field to test a few amounts and find the trade-off that fits your budget.
Debt snowball vs. debt avalanche
This calculator handles a single debt at a time. If you have several debts, two common strategies help you decide which one to attack first. You can run each debt through this tool, then apply the strategy across the set.
- Debt snowball: pay the minimum on everything, then throw extra money at the smallest balance first. When that one is gone, roll its payment into the next-smallest. This is built on motivation — quick wins keep you going.
- Debt avalanche: same idea, but target the highest interest rate first. Mathematically this saves the most interest, though the first payoff may take longer to arrive.
For a deeper comparison with examples, read our guide: Debt snowball vs. debt avalanche.
Related tools
- Paying down a card specifically? Use the Credit Card Payoff Calculator.
- Deciding between saving and paying down debt? See Emergency fund or pay off debt.
- Building the budget that funds these payments? Try the Monthly Budget Calculator.
Frequently asked questions
How is the debt payoff time calculated?
Each month the calculator adds interest using balance × APR / 12, subtracts your monthly payment (plus any extra), and repeats until the balance hits zero. The number of cycles is the payoff time.
How do extra payments change the result?
Extra payments reduce principal faster, so less interest accrues every following month. That shortens the payoff time and lowers total interest — often dramatically.
Is this the same as the debt snowball or avalanche method?
No. This tool models a single debt. Snowball and avalanche are ordering strategies for multiple debts. Use this calculator on each debt, then apply your chosen order.
Why does my real payoff differ from this estimate?
Real statements may use a daily balance method, late fees, changing minimums, promotional or penalty APRs, and different statement timing. This tool compounds monthly and ignores fees, so treat the result as an estimate.
Does this tool collect my financial information?
No. Everything runs in your browser. Nothing you type is sent to a server, stored, or tied to your identity.
Important note
This is an educational estimate. Actual payoff timing can change because of fees, promotional APRs, statement timing, and changes to your payment behavior. This page is not credit, lending, financial, tax, legal, or accounting advice. See our disclaimer for full details.