Credit card interest calculator

Estimate a cycle’s interest as average daily balance × annual rate/divisor × days charged.

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Average daily interest-bearing balance

Nominal annual interest (%)

More inputs and assumptions

Days charged

Rate divisor days per year

Answer

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Estimate a cycle’s interest as average daily balance × annual rate/divisor × days charged.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Step-by-step calculation

Inputs are substituted below. Each line evaluates the next operation; intermediate values are displayed to 12 significant digits while the calculation uses full precision.

Saved scenario

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Formula and assumptions

Use the average daily interest-bearing balance, not automatically the statement balance. Enter the agreement’s divisor. Grace periods, fees, promotional rates, daily compounding and changing APRs are not inferred.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Credit card interest calculator

Estimate a cycle’s interest as average daily balance × annual rate/divisor × days charged.

Next: Credit card payoff calculator

A worked example

Example inputs: average daily interest-bearing balance = 1000, nominal annual interest (%) = 18, days charged = 30, rate divisor days per year = 365. Estimated cycle interest = 14.7945205479.

Before you use the result

Example results for average daily interest-bearing balance

These examples use Nominal annual interest (%): 18; Days charged: 30; Rate divisor days per year: 365. They are reference calculations, not recommended settings.

Average daily interest-bearing balance	Estimated cycle interest
500	7.39726027397
1000	14.7945205479
2000	29.5890410959

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