Credit Card Debt Calculator: Payoff Time and Interest

A credit card debt calculator estimates how many months it will take to repay a balance at a fixed APR and monthly payment, plus the interest paid along the way. Enter your balance, APR, and payment; the results are an arithmetic estimate, not a lender payoff quote.

Formula

The calculator estimates the number of equal monthly payments needed to reduce a balance to zero while interest accrues monthly at APR divided by 12. It rounds the calculated payoff period up to a whole month, then multiplies that number by the entered payment to estimate total paid.

• B = starting balance, in dollars.
• a = annual percentage rate (APR), entered as a percentage per year.
• r = monthly rate as a decimal, equal to a / 1200.
• M = fixed monthly payment, in dollars.
• N = estimated months to repay: ceil(round(-ln(1 – rB/M) / ln(1 + r), 6)).
• Total paid = M × N, in dollars; estimated interest = total paid − B, in dollars.

The payoff formula assumes the payment is greater than the interest charged in the first month. If it is not, the balance will not decline under this model and the expression cannot produce a valid payoff estimate. Real card statements may calculate interest using daily balances, changing rates, fees, new purchases, and payment allocation rules, so the estimate can differ from an issuer’s figures.

Worked Example

Using the calculator’s defaults, the starting balance is $5,000, APR is 20%, and the payment is $200 per month.

1. Convert APR to a monthly decimal rate: r = 20 / 1200 = 0.0166667, or about 1.66667% per month.
2. Substitute into the payoff formula: N = ceil(round(-ln(1 – 0.0166667 × 5,000 / 200) / ln(1 + 0.0166667), 6)).
3. Calculate the expression: 1 – (0.0166667 × 5,000 / 200) = 0.5833333. The logarithm ratio is about 30.919, so rounding and then rounding up gives 31 months.
4. Total paid = $200 × 31 = $6,200.
5. Estimated interest = $6,200 − $5,000 = $1,200.

These figures use a full $200 payment in every modeled month, including the final month. In practice, the final payment may be smaller than the regular payment because only the remaining balance and accrued interest are due. The rounded-month method therefore makes total paid and interest simple estimates rather than an exact payment schedule.

Assumptions

• The APR stays fixed for the entire payoff period.
• Payments are made monthly and on time; the model treats the payment amount as level in each counted month.
• Interest compounds monthly at APR / 12, rather than being calculated from daily balances.
• No additional purchases, cash advances, late charges, annual fees, balance transfers, or other fees are included.

How to Use the Calculator

Use the balance currently subject to the rate you want to model, enter the APR shown for that balance, and choose a monthly payment amount. If a card has separate balances at different rates, one calculation cannot represent all of them accurately; calculate each portion separately or use the issuer’s payment information as a guide. Check whether a promotional rate or another rate change is scheduled, because this calculator assumes one rate from start to finish.

The first result is the estimated number of months. The following outputs translate that time into total payments and estimated interest. These depend on the payment being fixed; they do not show a month-by-month statement balance. A higher payment generally reduces the modeled payoff time, but the result is only valid when the payment covers accruing interest and reduces principal.

• For a payment amount, use the amount you intend to send each month toward this balance, not the card’s total credit limit.
• For APR, use the rate applicable to the balance, rather than a promotional or purchase rate that applies to a different portion.
• Recalculate after a rate, balance, or planned payment changes. Do not treat a result as a required minimum payment.

Why Credit Card Payoff Estimates Vary

Many card calculations use a daily periodic rate and the balance on each day, while this tool uses a monthly rate for a transparent estimate. The exact interest charge can also depend on transaction dates, the number of days in a billing cycle, when payments post, and whether new transactions are added. Because those details are not inputs here, the calculator cannot reproduce a statement exactly.

Minimum payments can change as the balance changes, and a minimum-payment amount may not remain level. This calculator does not infer a minimum payment from a card agreement: it requires you to enter a fixed amount. If that amount is too low to cover interest, no finite payoff time follows from the formula. A payment that only barely exceeds the interest may also produce a very long estimate.

Common Calculation Mistakes and Limits

• Mixing percentage formats: enter APR as 20 for 20%, not 0.20. The formula converts the percentage to a monthly decimal.
• Using the wrong balance: a card can have purchases, transfers, or cash advances at distinct rates. A single APR and balance may hide that difference.
• Assuming extra spending is included: new purchases increase the balance and can extend repayment; this model assumes no new charges.
• Reading a rounded estimate as a promise: payoff months are rounded upward, while actual interest and the final payment can vary with statement calculations and payment dates.

The calculation is useful for comparing hypothetical fixed payments under the same assumptions. It does not include taxes, insurance, or escrow, which are not components of this card-balance formula; nor does it model fees, card terms, or any effect on a credit score. Check the account statement or contact the card issuer for figures tied to the actual account.

Frequently Asked Questions

How do I calculate credit card debt payoff time?
Convert APR to a monthly rate by dividing by 1,200, then apply the fixed-payment payoff formula shown above. The payment must exceed the interest accruing each month for the balance to be repaid.

Does APR get divided by 12 or 1,200?
When APR is entered as a whole percentage, such as 20, divide by 1,200 to get a monthly decimal rate: 20 / 1,200 = 0.0166667. Dividing by 12 gives a percentage-point figure, not the decimal required in the formula.

Why does my card statement show different interest?
The calculator approximates interest with monthly compounding. An issuer may use daily balances, billing-cycle dates, transaction timing, fees, or changing rates, which can produce a different amount.

Can I use this calculator for several credit cards?
It estimates one balance at one APR and one fixed payment. For cards with different rates or payments, model each balance separately; the combined payoff schedule may depend on how payments are allocated and whether balances change.

What if my monthly payment is less than the interest?
The balance will not be paid off under the fixed-rate model if the payment does not exceed the interest charged. The calculator therefore cannot return a valid finite payoff estimate for that input combination.

This result is an estimate; the card issuer’s disclosure and account figures provide the exact amounts and terms.

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in bal | Credit card balance | $ | 5000 | 0.01 | 100000000
in apr | Interest rate (APR) | % | 20 | 0.01 | 100
in pmt | Monthly payment | $ | 200 | 0.01 | 100000000
out mon | Months to repay | months | ceil(round(-ln(1 - (apr / 1200) * bal / pmt) / ln(1 + apr / 1200), 6)) | 0
out tot | Total paid | $ | pmt * mon | 2
out int | Total interest | $ | tot - bal | 2