An unpaid balance accrues interest each period it stays outstanding. A Debt Calculator turns your balance, rate, and payment into a payoff timeline and total interest owed overall.
Calculate How Fast Extra Payments Pay Off a Credit Card or Personal Loan Balance
This calculator projects how long it takes to pay off a revolving or fixed-rate balance — a credit card, personal loan, or line of credit — when a set payment is made every period, plus an optional extra amount applied to principal. It’s built for anyone currently carrying a balance who wants to see how a bigger payment changes the payoff date and total interest, not for someone who already has a lender-calculated fixed-term loan payment.
Entering Your Balance, APR, and Payment Frequency
Enter the current balance, the card or loan’s APR (not a monthly finance rate), how often payments post — monthly, biweekly, or weekly — and the base payment plus any extra amount going toward principal. The output shows the payoff timeline, total interest, and interest saved by the extra payment. The calculator assumes a nominal annual rate split evenly across each payment period, not the daily-balance compounding some card issuers use on statements.
How the Payoff Timeline and Interest Are Calculated
Each period, interest is charged first: that period’s interest equals the prior balance multiplied by the periodic rate (the APR divided by the number of payments per year), the method the Consumer Financial Protection Bureau describes in its explanation of how loan amortization works.
Whatever remains of the payment after that interest charge reduces the principal, and the smaller balance carries into the next period — the calculation repeats period by period until the balance reaches zero. The periodic rate itself follows the Regulation Z convention reported in the Federal Reserve’s G.19 Consumer Credit release: a nominal annual rate divided by payment frequency, not a compounded effective rate.
$$I_t = B_{t-1} \times \frac{APR}{n}$$
$$B_t = B_{t-1} – (\text{Payment} – I_t)$$
The most common input mistake is entering a monthly rate — for example, a card’s stated 1.8% monthly finance charge — into the APR field, which the calculator then divides again by the payment frequency and understates interest by roughly a factor of twelve.
A second frequent error is setting the base payment below the first period’s interest charge; the calculator flags this as an invalid, non-amortizing input rather than a valid payoff. A third is treating the extra payment field as a single one-time lump sum instead of a recurring amount added every period, which produces a payoff date much later than expected.
The math holds for any balance above zero and any APR from 0% (a promotional balance-transfer rate, for instance) upward; a negative rate has no real-world equivalent and isn’t supported. If the base payment plus extra payment doesn’t exceed the first period’s interest charge, the balance never shrinks — that’s treated as an invalid input rather than an infinite payoff, since an ever-growing balance has no practical payoff date to report.
At the other extreme, a very small payment against a large balance can mathematically stretch past any realistic debt term; the calculation is capped at 50,000 payment periods as a safeguard against that boundary case.
Because each period’s interest is charged only on the balance still outstanding, an extra principal payment doesn’t just cancel out one period’s interest — it lowers every subsequent period’s balance too, so the same extra dollar amount saves more total interest the earlier it’s applied.
The APR and periodic-rate convention used here follows U.S. Regulation Z disclosure practice; the currency selector only changes the displayed symbol, not the underlying math, so anyone outside the U.S. should confirm their lender uses an equivalent periodic-rate method.
These figures are illustrative estimates based on the exact balance, rate, and payment entered — not a guarantee of what a specific issuer or lender will report, since real statements can involve daily-balance compounding, grace periods, and fee timing this simplified model doesn’t capture — and the results are for general education, not personalized financial, tax, or legal advice.
How the Interest-to-Principal Split Shifts as the Balance Shrinks
Early on, most of each payment covers interest on the still-large balance; by the last payment, nearly all of it reduces principal — the same mechanic that drives why extra payments made early in a payoff save more than the same amount paid later.
Average U.S. Credit Card APRs for Comparison (Federal Reserve Data)
| Measure | Average APR | Period |
|---|---|---|
| All credit card accounts (stated APR, all balances) | 20.94% | Q2 2026 |
| Accounts assessed interest (balances actually carried) | 22.15% | Q2 2026 |
Source: Federal Reserve Board, G.19 Consumer Credit release (terms of credit reported under Regulation Z), Q2 2026 data. These rates are U.S. commercial bank averages, reported quarterly and subject to change — confirm the current release before using a figure for an actual decision.
Common Questions About Payoff Timelines and Extra Payments
Does the extra payment need to be paid every period, or can it be a one-time payment?
This calculator assumes the extra amount recurs every period. A single one-time extra payment will still pay off the balance faster than making no extra payment, but not as fast as this tool’s ongoing extra-payment projection.
Is APR the same as the interest rate shown on my statement?
Usually close, but card issuers often calculate the actual finance charge from a daily average balance rather than this calculator’s per-period method, so the real interest charged can differ slightly from the projection here.
What happens if I set the payment lower than the interest charge?
The balance can’t shrink, since none of the payment reaches principal. The calculator treats this as an invalid input instead of a payoff date, because the debt would grow indefinitely rather than reach zero.
Does switching from monthly to biweekly payments change the results even at the same payment amount?
Yes. Biweekly payments post 26 times a year instead of 12, which works out to one extra full payment annually purely from the calendar — separate from anything entered in the extra payment field.
Can I use this for a mortgage or auto loan instead of a credit card?
The same interest-then-principal mechanics apply, but those loans usually have a lender-set fixed payment calculated to hit a specific term; entering your own payment here shows what happens if you pay more or less than that.
Why does the same extra payment save more interest on a high-rate balance than a low-rate one?
Interest each period equals balance times rate, so a higher rate makes every dollar of principal removed early worth more in avoided interest — extra payments have an outsized effect on high-APR debt like credit cards.