Free calculator
Credit card interest calculator
Estimate finance charges for one billing cycle from the average daily balance (ADB), nominal purchase APR, and days in the cycle. We show the daily periodic rate (APR ÷ 365) and rounded interest—illustration only; real statements use issuer rules, grace periods, and sometimes 360-day conventions we do not switch automatically.
When to use this calculator
A quick check for revolving interest accrual on one statement before you mirror the same math in Sheets or Excel.
- See about how much interest accrues when you carry a balance for one cycle at the APR you type—useful when your ADB is stable or you already know it from a statement footnote.
- Compare 365-day daily rate math to a spreadsheet cell so reviewers agree on APR/365 vs APR/360 questions (we default to 365; see FAQ).
- Pair with the credit card payoff tool when you need months to $0 and total interest over many payments—not the same question as one-cycle interest here.
We use the common textbook average daily balance method with a 365-day year: daily periodic rate = APR ÷ 100 ÷ 365, then interest = ADB × daily rate × days in the billing cycle. Money is rounded to cents for display.
Average daily balance
You enter one ADB number. We do not build a day-by-day ledger from purchases and payments—use your statement detail or a sheet when you need that level.
Daily periodic rate
APR is treated as a nominal annual purchase rate. The daily rate is APR ÷ 100 ÷ 365. Some issuers use 360 days in the divisor—your statement can differ; see FAQ.
Days in the cycle
Interest scales linearly with days in this simplified model—no mid-cycle grace-period logic on-page.
What we do not model
Grace periods (pay in full → often no interest on purchases), fees, cash-advance APRs, 0% promos, minimum payments, and multi-card balances—say so in FAQs when users expect those features.
This page is a teaching and spreadsheet-check aid. For paydown over time, open the credit card payoff calculator.
For savings growth with contributions, use the compound interest calculator.
Google Sheets & Excel
B2 = average daily balance, C2 = APR as a percent, D2 = days in cycle. Interest ≈ B2*(C2/100/365)*D2 for the same 365-day story as this page.
=B2*(C2/100/365)*D2Keep C2 as APR in percent form (e.g. 19.99), not as a decimal rate, so C2/100/365 matches this calculator.
In German Excel, argument separators are often ;—use Formulas → Insert function to match your language pack.
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Frequently asked questions
What does this credit card interest calculator do?
It estimates interest for one billing cycle from average daily balance, nominal APR, and number of days, using APR ÷ 365 as the daily periodic rate. It does not project months to payoff—use the payoff calculator for that.
How is this different from the credit card payoff calculator?
Payoff mode runs month-by-month with a fixed payment or target months until the balance hits zero. This page answers how much interest accrues in one cycle at the ADB and APR you type—different question, different math story.
What if I only know my statement balance, not ADB?
If your balance barely moved, using the statement balance as ADB is a rough check. If you had large purchases or payments mid-cycle, your real ADB is lower or higher—read your issuer disclosure or reconstruct daily balances in a sheet.
Why might my bank use 360 days instead of 365?
Some card agreements divide APR by 360 to get a daily periodic rate. That slightly increases the daily rate vs 365. This page defaults to 365 for clarity; adjust your sheet formula if your agreement says 360.
What about the grace period?
Many cards do not charge purchase interest when you pay the statement balance in full by the due date. We do not model grace-period rules—if you always pay in full, your interest may be $0 even when this math shows a non-zero line for a carried balance scenario.
Is APR the same as the rate on my statement?
Enter the nominal purchase APR that applies to the balance story you care about. Cash-advance APRs, penalty APRs, and promotional rates are separate lines on real statements—we only accept one APR here.
How do I match this in Google Sheets or Excel?
Use =ADB*(APR_percent/100/365)*days with APR as a percent cell, or see the copy card on this page. For paydown schedules, use NPER/PMT on the payoff PDP instead.
Is this debt or legal advice?
No. It is a free educational calculator—not a recommendation to borrow or carry balances, and not a substitute for qualified help when you are in financial distress.