Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate interest accrued on a credit card balance for a billing period, using the daily periodic rate.
$36.16
Credit card issuers typically calculate interest using a daily periodic rate (your APR divided by 365) applied to your balance each day of the billing cycle, not a single flat monthly calculation. This calculator estimates interest for a billing period using that same method, a genuinely different calculation than the month-by-month payoff simulation used elsewhere.
Enter your balance, APR, and the number of days in the billing period (30 is a common approximate cycle length).
Daily Periodic Rate = APR ÷ 365
Interest for Period = Balance × Daily Periodic Rate × Days
Real issuers commonly use an "average daily balance" method, applying the daily rate to your balance as it actually changes throughout the cycle (from purchases and payments), rather than a single flat balance for the whole period -- this calculator uses a simplified flat-balance approximation, which is close but not identical to your exact statement.
The example above uses a 30-day cycle. Because the formula is linear, you can adjust it for other cases. A 31-day cycle on the same $1,000 at 24% comes to about $20.38, since the daily rate of roughly 0.0658% is applied for one more day. A balance of $2,500 for the same 30 days would be about $49.32, exactly 2.5 times the original. Seeing these small differences helps you appreciate that the interest is proportional to three things: balance, rate, and days.
If your card has a grace period and you pay the full statement balance by the due date, new purchases usually accrue no interest at all. Once you carry a balance, that grace period is often lost, and interest may begin accruing from the purchase date on new charges too. This tool does not model grace periods, so treat its result as what you would owe if interest applies for the entire period. Check your cardholder agreement for the exact rules that apply to your account.
This is an estimate for a single billing period and a single balance. To see how long it would take to pay a balance off, use the Credit Card Payoff Calculator instead. For your exact charges, rely on your statement.
Most issuers use your average daily balance (which changes as you make purchases and payments throughout the cycle), not a single flat balance for the whole period -- this calculator's flat-balance method is a close approximation, not an exact match.
Yes -- most cards offer a grace period with no interest on new purchases if you pay your full statement balance by the due date every cycle; interest typically only accrues once you carry a balance past the due date.
Often yes, since many issuers compound daily. This tool uses a simple flat-balance calculation, so it may slightly understate the real charge.
Enter the days in your billing cycle, which is shown on your statement. Thirty is a common approximation.
Use the APR listed for the type of balance you have, since purchases and cash advances can differ.
You can multiply by twelve as a rough estimate, but it will only be accurate if your balance stays constant, which is rare.
Reference: Consumer Financial Protection Bureau