Credit Card Interest Calculator: One Month of Finance Charges
A credit card interest calculator estimates finance charges using an average daily balance and annual percentage rate. It is useful for understanding carrying cost, but an issuer’s exact result depends on transaction dates, grace periods, balance categories, fees, and compounding rules.
Quick answer
A 24% APR is roughly 0.0658% per day. On a $5,000 average daily balance over 30 days, that is about $98.63 in estimated interest before fees.
At a glance
- What it calculates
- Estimate one month of credit card interest from an average daily balance and APR.
- Who it is for
- US cardholders reconciling a statement finance charge or estimating the cost of carrying a balance for one cycle.
- Coverage
- United States (federal rules; state and local rules vary)
- Data and assumptions
- The average daily balance method with a daily periodic rate of APR divided by 365, applied to a single purchase balance with no grace period.
- Cost
- Free, no signup, calculations run in your browser
- Last reviewed
- 2026-07-09
Calculator
How to use this calculator
- Enter the average daily balance subject to interest.
- Enter the APR for that balance category.
- Enter the number of days in the cycle.
- Compare the estimate with the card agreement and statement.
Explanation
What it is
A credit card interest calculator estimates finance charges using an average daily balance and annual percentage rate. It is useful for understanding carrying cost, but an issuer’s exact result depends on transaction dates, grace periods, balance categories, fees, and compounding rules.
How it works
The estimate converts APR to a daily periodic rate and multiplies it by the average balance and number of days. Actual statements may separate purchases, cash advances, transfers, and promotional balances.
When to use it
Use it when reconciling a finance charge on a statement, or before deciding to carry a balance for one more billing cycle.
Limitations
- Issuers use different daily balance methods and rounding conventions.
- Promotional 0% APR periods, deferred interest and penalty APRs are not modelled.
- Fees, late charges and new transactions during the cycle are excluded.
Key terms
- APR
- Annual percentage rate used to express borrowing cost.
- Average daily balance
- The sum of daily balances divided by days in the cycle.
- Grace period
- A period in which purchases may avoid interest when conditions are met.
- Daily periodic rate
- APR divided by the number of days used by the issuer.
Formula
The estimate converts APR to a daily periodic rate and multiplies it by the average balance and number of days. Actual statements may separate purchases, cash advances, transfers, and promotional balances.
Worked example
At 24% APR, a $5,000 average balance over 30 days produces about $98.63 of estimated interest using a 365-day year.
FAQ
How much interest does a credit card charge per month?
A simple monthly approximation is balance times APR divided by 12, but many issuers use an average daily balance and a daily periodic rate.
Why is my interest charge different from this estimate?
Transaction timing, prior balances, compounding, separate APR categories, fees, and the issuer’s day-count method can change the charge.
Do I pay interest if I pay the statement balance in full?
Many cards provide a purchase grace period when the full statement balance is paid by the due date, but terms vary and cash advances commonly accrue interest immediately.
How can I reduce credit card interest?
Reduce the average balance sooner, pay more than the minimum, avoid new charges, and consider lower-cost options only after comparing fees and terms.
Is 0% APR completely free?
Promotional offers may still have transfer fees, end dates, eligibility conditions, and a higher standard APR after the promotion.
Does credit card interest compound daily?
Most US issuers apply a daily periodic rate (APR ÷ 365) to the average daily balance, and unpaid interest is added to the balance at the end of the cycle, so interest effectively compounds monthly on a daily-calculated basis.
How much interest do credit cards charge per month?
At a 22% APR, one month of interest on a $3,000 average daily balance is roughly $55. The monthly cost is about 1.83% of the balance carried, which is the APR divided by 12.
Common mistakes
- Using the closing balance instead of the average daily balance.
- Applying one APR to a card that has separate purchase, transfer and cash advance rates.
- Assuming a payment made after the statement date removes interest for that cycle.
- Overlooking residual (trailing) interest on the following statement.
Tips
- Use the average daily balance from the statement, not the closing balance.
- Divide the purchase APR by 365 to get the daily periodic rate the issuer applies.
- Calculate cash advance and balance transfer balances separately; they carry different APRs.
- Paying the full statement balance by the due date usually restores the purchase grace period.
Sources and editorial review
Educational estimates only; not personalized financial, tax, legal, lending, investment, or insurance advice.