Credit Card Interest Calculator

Card issuers convert your annual percentage rate into a periodic rate, then apply it to a balance. Two periodic rates are common: a monthly periodic rate (APR / 12) used for headline math and many statements outside the US, and a daily periodic rate (APR / 365) used inside the US. With the daily rate, the issuer multiplies it by the balance each day across the billing cycle. On most US cards, that day-by-day total is then averaged into the average daily balance and interest equals that average times the daily rate times the days in the cycle.

If you want a quick headline number that matches the way most US online payoff schedules are illustrated (including the FTC and CFPB examples), pick monthly periodic. If your statement quotes a daily periodic rate (most major US issuers do), pick daily periodic or average daily balance to mirror that. With a single balance entered, daily periodic and average daily balance produce the same one-month figure, because there is only one balance to average. The 12-month projection always uses the monthly periodic rate so the time series stays comparable across methods.

Because interest compounds. Even when you make a monthly payment, the next month starts with a balance that has had interest added to it, so the dollar charge does not fall as fast as the balance does. At a typical 22% to 23% US card APR, the first 12 months of interest on a $5,000 balance with a $200/month payment can run more than $750, almost an extra 15% on top of the original balance.

The balance grows when your payment is below the monthly interest charge. If the payment exactly equals the interest charge, the balance stays flat because no principal is repaid. In either case, the calculator shows the months-to-payoff value as not applicable.

No. The calculator assumes you stop using the card and only carry the balance you entered, so no new purchases, no late fees, no annual fees, no cash advance APRs. In real life, putting new charges on a card that already carries a balance usually means the entire new total accrues interest from day one, because you lose the interest-free grace period until the balance is paid in full. If your situation involves ongoing purchases, the figures here are a floor on what you will actually pay, not a ceiling.