Credit Card Payoff Calculator: Time and Interest

A credit card payoff calculator estimates how many months it may take to clear a balance and how much interest you may pay when you make a fixed monthly payment. Enter your current balance, annual percentage rate (APR), and planned payment; the results are estimates based on a constant rate and monthly calculations.

Formula

The calculator models a fixed monthly payment on a balance accruing interest each month. It first estimates the number of payments with the standard level-payment formula, rounding the number of months up to a whole month:

n = ceil(round(−ln(1 − r × B / M) ÷ ln(1 + r), 6))

• B is the starting card balance in dollars.
• A is the APR entered as a percentage per year.
• r is the monthly rate, calculated as A ÷ 1,200.
• M is the fixed payment in dollars per month.
• n is the estimated number of monthly payments.

The other results are total paid = M × n and estimated interest = total paid − B. The payment formula assumes a payment at each monthly period and a fixed rate. It treats the final payment as equal to the regular payment, so total paid and interest may be overstated when the remaining balance would require a smaller final payment. The calculator does not model a minimum payment that changes over time or the exact final payment.

Worked Example

Using the default inputs—$5,000 balance, 20% APR, and $250 monthly payment—the monthly rate is 20 ÷ 1,200 = 0.0166667, or about 1.6667%.

1. Calculate the payment ratio: r × B ÷ M = 0.0166667 × $5,000 ÷ $250 ≈ 0.333333.
2. Calculate the logarithms: −ln(1 − 0.333333) ÷ ln(1 + 0.0166667) ≈ 24.47 months.
3. Round up to a whole payment period: n = 25 months.
4. Estimated total paid: $250 × 25 = $6,250.
5. Estimated interest: $6,250 − $5,000 = $1,250.

The calculator therefore returns 25 months, followed by an estimated total of $6,250 and interest of $1,250.

Assumptions

• The APR stays fixed throughout the payoff period.
• Payments are made monthly, at the end of each monthly period.
• Interest is modeled with monthly compounding at APR ÷ 12.
• No new purchases, cash advances, balance transfers, late charges, fees, taxes, or changes in payment are included.

How to Use and Read the Estimate

Use the balance currently owed, rather than the card’s credit limit. Enter the APR that applies to that balance; a card may have different rates for purchases, transfers, and cash advances, so a single APR may not represent every part of a mixed balance. Enter the payment amount you expect to make every month. The output is a mathematical estimate, not a statement of what the card issuer will charge or require.

The displayed payoff time is rounded up because a fractional month still requires another payment period under this model. Total paid is the monthly payment multiplied by the full number of periods, and estimated interest is the difference between that total and the starting balance. These totals are internally consistent with the stated fixed-payment assumption, but real account statements can differ.

For example, actual card interest is commonly based on daily balances and the issuer’s billing-cycle rules. A payment’s date, new transactions, promotional-rate expiration, fees, or a variable APR can change the result. If you make payments on different dates or amounts, this fixed-payment estimate will not reproduce the account’s exact schedule.

Choosing a Payment Amount and Common Problems

The payment must exceed the interest accruing for the period for the balance to decline. In this formula, that means the monthly payment must be greater than the starting balance multiplied by the monthly rate. If it does not, the logarithm cannot produce a finite payoff time; the calculator may show “Cannot compute.” That does not mean the debt disappears or that the card issuer will accept that payment. It means the entered amount does not repay the modeled balance.

One common misconception is that paying the minimum will produce a fixed payoff date. Credit-card minimums are often determined by account terms and can change as the balance changes. This calculator instead holds the payment constant, so it cannot forecast a minimum-payment schedule. Check the card’s statement or account terms for the required minimum and the issuer’s payoff disclosures.

• Check APR units: enter an annual percentage, such as 20, not the monthly rate of 1.6667.
• Use a payment amount in dollars: do not enter a percentage of the balance.
• Consider new charges separately: purchases added during repayment can extend payoff time and add interest.
• Do not treat rounded outputs as exact: the model rounds months to whole periods and does not calculate a smaller final payment.

Limits and Other Payoff Methods

This calculation is useful for understanding how a fixed payment relates to time and interest, or for comparing hypothetical payment amounts while holding the other inputs constant. It is not a personalized debt plan, and it does not account for income, essential expenses, other debts, promotional terms, or account-specific minimum-payment rules.

Other ways to model a payoff include a month-by-month amortization schedule using actual payment dates and daily interest, or separate calculations for each balance when a card has multiple APRs. A balance-transfer or consolidation scenario also requires its own inputs, including applicable fees, rates, and repayment terms. The calculator does not assume those options are available or evaluate whether they suit a person’s circumstances.

Frequently Asked Questions

How long will it take to pay off my credit card?
It depends on the balance, APR, and payment amount. Enter those figures to get an estimate under a fixed monthly payment assumption; actual account terms and activity can change the timing.

Why does the calculator say it cannot compute?
The entered payment may be no greater than the interest the model adds each month. A payment must exceed that monthly interest for the balance to be repaid under this formula.

Does this calculator use the minimum payment?
No. It assumes the same dollar payment every month. Minimum-payment amounts can change, so a minimum-payment payoff schedule needs the card’s specific calculation rules.

Why is my statement’s interest different?
The calculator uses monthly compounding and a fixed rate, while an issuer may calculate interest from daily balances and billing-cycle details. New charges, payment timing, fees, and rate changes can also affect the statement.

Does the estimate include new purchases or fees?
No. It assumes the balance receives no new charges and excludes fees and other account adjustments.

This result is an estimate for educational purposes; the card issuer’s disclosures and account statements give the exact figures.

Related

• Calculate Loan Interest on a Reducing Balance
• Base e and Compound Interest Explained
• Balance Subject to Interest Rate? How It Works

in bal | Credit card balance | $ | 5000 | 0.01 | 100000000
in apr | Interest rate (APR) | % | 20 | 0.01 | 100
in pay | Monthly payment | $ | 250 | 0.01 | 100000000
out mon | Months to pay off | months | ceil(round(-ln(1 - (apr / 1200) * bal / pay) / ln(1 + apr / 1200), 6)) | 0
out tot | Total paid | $ | pay * mon | 2
out int | Estimated interest | $ | tot - bal | 2