Credit Card Interest Calculator
Enter your balance and APR. We estimate this month's interest charge and what the balance would cost over a year if you did not pay it down.
This calculator gives estimates for information only. It is not financial, tax or legal advice. Real results depend on lender terms, fees and local rules.
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The formula
Interest = balance x (APR / 365) x days in the cycle. Cards usually compound this daily.
How card interest is charged
Most cards divide your APR by 365 to get a daily rate, and apply it to your balance each day. A 3,000 balance at 24 percent APR costs about 59 in a 30-day cycle.
The grace period
If you pay your full statement balance by the due date every month, most cards charge no interest on purchases. Interest only starts when you carry a balance. Cash advances usually have no grace period.
What carrying a balance costs
That same 3,000 would cost about 805 in interest over a year at 24 percent if you made no payments, which is why paying more than the minimum is so valuable. The credit card payoff calculator shows how fast you can clear it.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Card balance ($): 3000; APR (%): 24; Days in billing cycle: 30 | Interest this billing cycle: $59.18 |
| Card balance ($): 1500; APR (%): 19.99; Days in billing cycle: 31 | Interest this billing cycle: $25.47 |
| Card balance ($): 8000; APR (%): 27; Days in billing cycle: 30 | Interest this billing cycle: $177.53 |
Credit Card Interest Calculator: frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated on the original amount only. Compound interest is calculated on the amount plus the interest already earned, so it grows faster over time.
Is this financial advice?
No. It gives an estimate from the numbers you enter. Real offers depend on fees, tax and the lender or provider, so check the terms before you commit.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026