Finance Charge Calculator
A $1,000 balance at an 18% APR over a 30-day billing cycle adds about $14.79 in finance charge. This finance charge calculator estimates card interest from your purchase balance, APR, and billing-cycle length using a simple daily periodic rate. It works best when the balance stays unchanged for the full cycle. This is an interest estimate, not a reconstruction of a credit card statement. It divides APR by 365 and applies that daily rate to one balance for every day entered. Card issuers may use average daily balance, separate balances for purchases and cash advances, transaction dates, compounding, minimum interest charges, and grace-period rules. Fees can be called finance charges in some disclosures, but this calculator does not add them.
Quick answer
This tool turns APR into a daily periodic rate by dividing the annual rate by 365.
This estimate uses a simple daily periodic rate with a 365-day year and assumes the same balance is carried every day of the cycle.
What this tells you
- •This tool turns APR into a daily periodic rate by dividing the annual rate by 365.
- •The finance charge rises with a larger balance, a higher APR, or a longer billing cycle.
- •This estimate assumes the same balance is carried every day of the cycle and focuses on the interest portion of the finance charge.
- •The calculation uses a 365-day denominator even when the billing cycle falls in a leap year.
- •Payments, purchases, credits, and fees during the cycle are not modeled.
- •An APR of 0% produces no interest in this model, though account fees may still apply.
How to Use
- 1Enter the purchase balance you expect to carry through the billing cycle.
- 2Enter the APR from your card agreement or statement as a percent, such as 18 for 18%.
- 3Enter the billing-cycle length in whole days.
- 4Calculate to see the estimated finance charge, the total balance after the charge, and the daily rate used in the math.
- 5Compare the estimate with the interest calculation section of your cardholder agreement.
- 6Use an average daily balance or statement-specific method when the balance changed during the cycle.
How It Works
Formula
Daily rate = APR ÷ 365
Finance charge = Purchase balance x (APR ÷ 365) x Billing-cycle days
Total balance = Purchase balance + Finance charge
Example: $1,000 x (0.18 ÷ 365) x 30 = $14.79APR must be written as a decimal before you divide by 365 to get the daily periodic rate. That daily rate is applied to the balance for each day in the billing cycle. This tool uses a simple estimate, so it assumes the balance does not change during the cycle.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
A $1,000 balance at 18% APR for 30 days
An 18% APR becomes about 0.0493% per day in this calculator. Apply that daily rate across 30 days and the estimated finance charge is $14.79.
A $2,500 balance at 24% APR for 25 days
$2,500 x (0.24 / 365) x 25 equals $41.0959, which rounds to a $41.10 finance charge. Adding it to the unchanged balance gives $2,541.10.
A $750 balance at 0% APR for 31 days
A 0% APR produces a daily interest rate of zero, so this model adds no interest. A real account could still charge annual, late, transfer, or other fees.
A $5,000 balance at 29.99% APR for 31 days
$5,000 x (0.2999 / 365) x 31 equals $127.3548, which the calculator displays as $127.35 after its two-decimal rounding. Adding that charge gives a total of $5,127.35.
A $1,200 balance at 15% APR for 28 days
$1,200 x (0.15 / 365) x 28 equals about $13.81. This example treats $1,200 as the balance on every one of the 28 days.
Estimated Finance Charge on a $1,000 Balance
These examples use the same simple daily-rate method as the calculator above and assume the balance stays unchanged for the whole cycle.
| APR | 25-day cycle | 30-day cycle | 31-day cycle |
|---|---|---|---|
| 15% | $10.27 | $12.33 | $12.74 |
| 18% | $12.33 | $14.79 | $15.29 |
| 24% | $16.44 | $19.73 | $20.38 |
Small changes in APR or cycle length can move the charge more than most cardholders expect, especially on a balance carried month after month.
Why a statement charge may use different math
The daily periodic rate in this calculator is APR as a decimal divided by 365. An 18% APR becomes about 0.00049315 per day, or 0.0493% when displayed as a percentage. Multiplying that decimal rate by balance and days estimates simple interest for one cycle. The displayed daily rate is rounded to four decimal places, but the finance charge uses the unrounded rate.
Credit cards commonly use an average daily balance. The issuer records the balance for each day, adds those daily balances, and divides by the number of days in the cycle. Purchases, payments, credits, and their posting dates can therefore change the charge. Entering the ending statement balance here may overstate or understate interest if that balance was not present for the full cycle.
A single account can have separate APR buckets for purchases, balance transfers, cash advances, or promotional offers. Grace periods may prevent purchase interest when the statement balance is paid as required. Cash advances may start accruing interest immediately. Fees, penalty APRs, residual interest, and minimum charge provisions require the account agreement, so this three-input model cannot reproduce them.
Common mistakes
- Using the statement balance when part of it did not stay on the card for the full cycle
- Mixing up APR with the daily periodic rate shown on a statement disclosure
- Forgetting that late fees, cash-advance fees, and average daily balance rules can raise the actual finance charge
- Entering the daily rate in the APR field instead of the annual percentage rate
- Using the ending balance as though it had remained unchanged since the first day of the cycle
- Adding account fees to the balance and then describing all calculated interest as the fee itself
- Assuming APR divided by 12 will match a daily-rate statement calculation for every cycle length
Limitations
This calculator uses simple interest with a daily periodic rate based on a 365-day year and assumes the same purchase balance is carried every day of the billing cycle. It does not model daily balance changes, compounding within the cycle, posting dates, payment allocation, grace periods, residual interest, minimum interest, promotional expiration, penalty APRs, separate purchase and cash-advance balances, or any fees. Some products use a 360-day denominator or other contract terms. The total balance shown merely adds this estimated interest to the entered balance and does not predict the next statement balance.
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