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Credit card interest calculator

Enter your balance, APR and billing cycle to see the interest charge the way card issuers work it out. Add a purchase and a payment to see how timing changes it.

By the Calcist team · Checked against known answers · Updated October 28, 2026

Minimum payment rule

Private: calculated on your device. Nothing you type is sent anywhere.

Estimates for planning, not financial, tax or legal advice. Figures use US rules unless the page says otherwise.

Next: Ready to plan your way out? The credit card payoff calculator sets a payment or a payoff date, and the debt payoff calculator handles several cards.

What APR means on a credit card

The APR is the yearly interest rate on the balance you carry. Card issuers don't charge it once a year. The CFPB explains that many issuers use a daily periodic rate: the APR divided by 365 (or 360), applied to what you owe at the end of each day.

How the interest charge is calculated

Daily periodic rate = APR ÷ 365
Average daily balance = (sum of each day's balance) ÷ days in the cycle
Interest = daily periodic rate × average daily balance × days in the cycle

The CFPB adds that this interest is added to your balance, so it compounds. The result also shows the slightly higher figure you'd get if interest compounds every day.

Worked example

A $3,000 balance at 24% APR over a 30-day cycle: the daily rate is 24% ÷ 365 = 0.065753%. Interest = 0.00065753 × 3,000 × 30 = $59.18.

Now pay $1,000 on day 11 and make a $500 purchase on day 16. The balance is $3,000 for 10 days, $2,000 for 5 days and $2,500 for 15 days, so the average daily balance is $2,583.33 and the interest falls to $50.96. Paying earlier in the cycle cuts the interest, even when the total paid is the same.

Interest on purchases and the grace period

According to the CFPB, you may not be charged interest on purchases if you pay your balance in full by the due date. Issuers must get your bill to you at least 21 days before the payment is due. If you carry a balance, you lose that grace period, and new purchases start costing interest from the day you make them. Cash advances usually have no grace period. This calculator assumes you're carrying a balance.

The minimum-payment trap

The result also shows how long the balance takes to clear if you pay only the minimum. Here the minimum is 1% of the balance plus that month's interest, or $25, whichever is greater. That rule varies by issuer, so you can change it. Because the minimum shrinks with the balance, it can take many years. On $5,000 at 22%, it takes 18 years 11 months.

The Credit CARD Act made this visible: under Regulation Z, your statement must carry a "Minimum Payment Warning", say how long paying only the minimum would take and what it would cost, and show the monthly payment that clears the balance in 36 months. This calculator shows the 36-month payment too.

Limitations

  • Issuers differ on details: some use APR ÷ 360, some compound daily, and cards with several APRs (cash advance, balance transfer) apply payments in set ways.
  • Fees and promotional rates aren't included.
  • To plan a payoff by a set payment or date, use the credit card payoff calculator.

Sources

How we checked this

Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:

  • $3,000 at 24% APR, 30-day cycle, ÷365: $59.18 interest ✓
  • Daily periodic rate 24% ÷ 365 = 0.065753% ✓
  • $500 purchase on day 16 and $1,000 payment on day 11: average daily balance $2,583.33, interest $50.96 ✓
  • 31-day cycle with a 360-day year: $62.00 ✓
  • $5,000 at 22% paying the minimum (1% + interest, $25 floor): 18 years 11 months ✓
  • Same: 36-month payoff needs $190.95 a month ✓
  • $20 balance: the $25 floor clears it in 1 month ✓

Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.

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Questions people ask

How is credit card interest calculated?

Most issuers multiply a daily periodic rate (APR ÷ 365 or 360) by your average daily balance and the number of days in the billing cycle. $3,000 at 24% for 30 days is about $59.18.

What is APR on a credit card?

It's the yearly interest rate on balances you carry. Divided by 365, it gives the daily periodic rate the card charges each day.

How do I avoid interest on purchases?

Pay the full statement balance by the due date each month. The grace period then usually covers new purchases, but not cash advances.

How long will it take to pay off a credit card paying the minimum?

With a minimum of 1% plus interest (at least $25), a $5,000 balance at 22% takes 18 years 11 months and costs $7,963.70 in interest.

What is a daily periodic rate?

The APR divided by 365 or 360, depending on the issuer. At 24% APR it's about 0.0658% a day.

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