Credit Card Interest Calculator
Calculate how long a credit-card balance takes to pay off at a fixed monthly payment, and the total interest you will pay at a given APR.
How to use this tool
- Enter your current card balance.
- Enter the purchase APR.
- Enter the fixed monthly payment you will make.
- Read the months to pay off, total interest, and total paid.
See how long a credit-card balance takes to clear at a fixed payment and how much interest you will pay. Enter the balance, APR, and monthly payment.
Formula
Each month the balance accrues interest at the monthly rate r = APR ÷ 12:
Interest = Balance × r, then the payment covers that interest and the rest reduces principal.
The simulation repeats until the balance reaches zero; the final month pays only what remains.
If the payment is not greater than the first month's interest, the balance never clears.
How it works
This calculator answers the two questions that matter most about a card balance: how long will it take to clear at a fixed payment, and how much interest will that cost? It simulates the balance month by month using the monthly periodic rate (APR ÷ 12). Each month interest is added, the payment is applied — interest first, the remainder to principal — and the loop continues until the balance reaches zero, with a clean final partial payment.
The single most important check is that your payment exceeds the first month's interest; if it does not, the balance grows forever and the tool returns a flag. This model assumes a fixed payment and a constant APR with no new charges; real statements may compound daily and add purchases, so treat the result as a close planning estimate. Raising the payment even modestly cuts both the months and the total interest sharply, which the calculator makes easy to test.
Reviewed by the AbraCalc Credit Desk. This is general information, not financial advice; confirm your card's terms (APR, fees, minimum-payment rule) with your issuer or a qualified advisor.
Worked example
$1,200 at 0% APR, $100/month
- At 0% APR no interest accrues, so every payment reduces principal.
- 1,200 ÷ 100 = 12 equal payments.
- Total interest = 0; total paid = 1,200.
Months to pay off = 12, total interest = $0.00
Months to pay off $1,000 at 12% APR by monthly payment
| Monthly payment | Months to pay off | Total interest |
|---|---|---|
| $50 | 22 months | $110.40 |
| $100 | 11 months | $58.13 |
| $150 | 7 months | $35.65 |
| $200 | 6 months | $31.12 |
| $250 | 5 months | $25.50 |
| $500 | 3 months | $15.05 |
Key terms
- Annual percentage rate (APR)
- The yearly interest rate on the card; the monthly rate is APR ÷ 12.
- Monthly periodic rate
- APR divided by 12 — the rate applied to the balance each month in this model.
- Fixed monthly payment
- A constant amount paid every month; higher payments cut both time and total interest.
- Total interest
- The sum of all interest charged from now until the balance reaches zero.
Frequently asked questions
- Why does a small extra payment cut the time so much?
- Once the payment clears the monthly interest, the entire extra amount reduces principal, which lowers next month's interest too. The effect compounds, so a modest increase shortens payoff and cuts total interest sharply.
- What happens if my payment is too small?
- If the payment does not exceed the first month's interest, the balance grows instead of shrinking and never clears. The calculator returns a flag in that case.
- Does this account for new purchases?
- No. It assumes a fixed payment, a constant APR, and no new charges. Adding purchases extends payoff and increases total interest beyond the estimate.