Credit Card Interest Calculator

How credit card interest is actually calculated

Card issuers do not simply charge your annual percentage rate (APR) once a year. They convert it into a daily periodic rate and apply it to your balance every single day of the billing cycle, then add up those daily charges to get your monthly finance charge. The formula issuers use looks like this:

Daily periodic rate = APR ÷ 365

Daily interest = average daily balance × daily periodic rate

Monthly interest charge = sum of daily interest over the billing cycle (commonly 28 to 31 days)

The 'average daily balance' matters because your balance rarely stays flat all month. Every purchase, payment and refund shifts it, and the issuer averages the balance across every day of the cycle rather than just looking at the balance on your statement date. This calculator uses a simplified 30-day approximation of that same math for the quick answer at the top, then switches to a full month-by-month amortization simulation for the payoff timeline below, applying a monthly rate (APR ÷ 12) to whatever balance remains at the start of each month.

Worked examples

Three quick scenarios show how much APR and payment size change the outcome:

• $3,000 balance, 22% APR, $150 monthly payment: about 26 months to pay off, roughly $771 in total interest.
• $3,000 balance, 22% APR, $90 monthly payment (closer to a typical minimum): about 52 months to pay off, roughly $1,679 in total interest, more than double the interest for a payment 40% smaller.
• $8,000 balance, 27.99% APR, $300 monthly payment: about 43 months to pay off, roughly $4,659 in total interest, a reminder of how much a high APR compounds over a longer payoff.

Typical interest by APR and balance (rough monthly estimate)

These figures use the same 30-day quick-estimate formula as the calculator above (balance × APR ÷ 365 × 30) and assume no payment is made that month, so you can sanity-check the tool's output against a reference table. Your actual first-month charge will usually be somewhat lower once payments start reducing the balance mid-cycle.

Purchase APR, cash advance APR and penalty APR are not the same

Most cards actually carry several different APRs at once, and the calculator above uses whichever rate you enter, so it's worth knowing which one applies to your situation. The purchase APR is what most people mean by 'my card's interest rate,' and it's the one that applies to everyday spending, but only once you're carrying a balance past your due date, since paying in full every cycle avoids interest on purchases entirely thanks to the grace period. A cash advance, by contrast, usually carries a higher APR and starts accruing interest immediately with no grace period at all, plus its own fee, which is different enough that it gets its own cash advance interest calculator on this site. A penalty APR can kick in after a late payment and is typically the highest of the three, sometimes applied to your whole balance rather than just new purchases.

Minimum payment vs. paying more

The calculator above automatically runs both scenarios side by side: what happens if you only ever pay the minimum, and what happens with the payment (or target date) you entered. The minimum payment itself isn't fixed. It typically shrinks every month as your balance drops, following a formula like the greater of a flat floor (often $25) or your interest charge plus 1 to 3% of the balance, which is exactly why minimum-only payoffs stretch out for years even on a modest balance. See the dedicated minimum payment calculator for a closer look at that formula and a month-by-month simulation of what minimum-only payments really cost.

What happens if you pay late

Missing a due date usually triggers two separate costs, and it's worth understanding both because they compound with the interest math above. First, most cards charge a flat late fee, commonly in the $30 to $41 range, added directly to your balance on the date it's assessed. Second, and often more expensive over time, a late payment (especially one that's 60 days or more overdue) can trigger a penalty APR, which is frequently well above your standard purchase APR and can apply to your entire existing balance, not just new charges. Some issuers will reduce a penalty APR back to your standard rate after a run of on-time payments, typically six consecutive months, but that isn't universal, so it's worth checking your card's specific terms. If you think a penalty APR has been applied, plug that higher rate into the calculator above to see the real cost difference versus your normal APR.

Statement balance vs. current balance

Two numbers on your account can both reasonably be called your 'balance,' and mixing them up leads to a wrong interest estimate. Your statement balance is a snapshot taken on your statement closing date, the amount your minimum payment and due date are based on. Your current balance includes anything that's posted since then, new purchases, payments, refunds, and it's a moving target throughout the cycle. For the calculator above, your current balance is the more accurate input if you want to know what you'll be charged going forward, since interest accrues on the average daily balance across the cycle, not on a single fixed statement snapshot. If you're not sure which figure you're looking at, your issuer's app or online portal almost always labels both separately.

Interest charges vs. credit utilization: two different numbers

It's common to mix these up, but they measure different things and only one of them is what this calculator computes. Interest is the dollar cost of carrying a balance, the finance charge calculated from your APR and average daily balance, exactly what the tool above estimates. Credit utilization is a percentage, your balance divided by your credit limit, and it's a factor credit scoring models use, independent of whether you're actually charged any interest that month. A card paid in full every month can still show meaningful utilization on your statement closing date even though zero interest accrues, because utilization is a snapshot of balance-to-limit, not a measure of cost. If you're trying to improve a credit score, lowering utilization (paying down balances, or asking for a higher limit) is the relevant lever; if you're trying to spend less on finance charges, the payment strategies and APR comparisons above are the relevant ones. The two goals often point in the same direction (pay down balances) but they are not the same calculation.

Where your numbers go when you use this calculator

Nowhere but your own browser. Every field above is calculated entirely on your device using JavaScript, your balance, APR and payment are never sent to a server, logged, or stored anywhere. See the full privacy policy for details on exactly what this site does and does not collect.

How to reduce the interest you actually pay

None of these require refinancing or a new card, though a lower-rate option can help too:

• Pay more than the minimum whenever you can, even an extra $20 to $50 a month meaningfully shortens the payoff timeline because it attacks principal instead of just covering interest.
• Pay before your statement closes, not just before the due date, since the average daily balance the issuer calculates interest on is lower the sooner in the cycle your payment lands.
• If your card has a grace period and you carried no balance last cycle, paying your full statement balance by the due date avoids interest on new purchases entirely.
• Avoid cash advances where possible: they skip the grace period and usually carry a higher APR plus an upfront fee (see the cash advance calculator above).
• A 0% introductory APR balance transfer can pause interest accrual entirely for a promotional period, though transfer fees and the rate that applies afterward both matter to the math.