Daily Periodic Rate Calculator and Formula

A daily periodic rate is the interest rate applied to a balance for one day. Enter the annual percentage rate (APR) to calculate the daily rate, expressed as a percentage or decimal; the result is a rate, not a dollar amount of interest.

Formula

For the standard 365-day calculation, divide the annual percentage rate by 365:

Daily periodic rate (%) = APR (%) ÷ 365

• APR is the annual percentage rate entered as a percentage, such as 18 for 18% per year.
• Daily periodic rate is the rate for one day, shown here as a percentage.
• Daily rate as a decimal is the percentage divided by 100, in a form that can be multiplied by a balance to estimate one day’s interest.

The calculator assumes a 365-day year. Some financial products use a different day-count convention, such as 360 days or the actual number of days in a year. Use the convention stated in the account or loan terms when it differs from this calculation.

Worked Example

Using the calculator’s default APR of 18%:

1. Divide the APR by 365: 18 ÷ 365 = 0.0493150685 percentage points per day.
2. Rounded to six decimal places, the daily periodic rate is 0.049315%.
3. Convert the percentage to a decimal by dividing by 100: 0.0493150685 ÷ 100 = 0.000493150685.
4. Rounded to eight decimal places, the daily rate as a decimal is 0.00049315.

These results are the per-day rate. To estimate one day of interest on a balance, multiply the balance by the decimal rate. For example, on a constant $1,000 balance, the unrounded estimate is $1,000 × 0.000493150685, or about $0.49 for one day.

Assumptions

• The APR is treated as a fixed annual rate for this calculation.
• The rate is divided by 365; daily accrual is represented as one day at that periodic rate.
• This rate conversion does not model payment timing, compounding over multiple days, or changes in the balance.
• Fees, taxes, insurance, and other charges are not included.

How the Daily Rate Works

A periodic rate is the interest rate applicable to a particular interval. A daily periodic rate applies to one day; a monthly periodic rate applies to a month. In a simple daily-interest estimate, the daily rate is multiplied by the balance subject to interest. If that balance changes, the interest estimate changes too.

For example, multiplying the decimal daily rate by a balance estimates interest for one day only. Over several days, a calculation might apply the rate each day to the balance for that day. If interest is added to the balance and then itself accrues interest, compounding affects the cumulative amount. The calculator does not project that process or calculate a bill, payoff amount, or total interest for an account.

Also distinguish a periodic rate from APR. APR is an annualized rate shown as a percentage per year; the daily periodic rate is a per-day rate derived from it using a chosen day-count convention. They are related but not interchangeable. A quoted APR may also be defined or disclosed differently depending on the product and its terms, so the contract’s stated rate and calculation method matter.

When to Use It and How to Read the Result

Use this calculation when you need to convert an APR into an estimated daily rate using a 365-day denominator. It can help explain how a daily rate is derived or provide the rate component for a separate estimate. Check the account or loan disclosure for the APR and the method used to accrue interest before relying on a calculation.

• The first output is the daily rate as a percentage. At the default 18% APR, that is 0.049315% per day after rounding.
• The second output is the same rate as a decimal. Use this form when multiplying by a balance.
• For an approximate one-day amount, use: balance × daily rate as a decimal. Keep extra precision during the calculation, then round the resulting money amount as appropriate.

Do not read 0.049315% as 4.9315%. The percent sign matters: 0.049315% equals approximately 0.00049315 as a decimal. Multiplying by the percentage number without converting it to a decimal would overstate the estimate by a factor of 100.

Day-Count Methods and Related Calculations

A 365-day divisor is a common way to express an annual rate per day, but it is not universal. A 360-day convention produces a different daily periodic rate from the same APR. Some calculations may use actual calendar days and account for leap years or the precise number of days in a period. The applicable method is determined by the product’s terms, not by this calculator.

For comparison, at an 18% APR, dividing by 360 gives 0.05% per day, while dividing by 365 gives about 0.049315% per day. The difference comes from the denominator, not a different APR. Do not substitute one convention for another just because it produces a convenient result.

To estimate interest across multiple days, you need more than the daily rate if the balance varies, payments or charges occur, or interest compounds. The calculation must follow the account’s timing and balance rules. This tool isolates the rate conversion so those details are not silently assumed.

Common Mistakes and Limits

• Mixing percent and decimal forms: 18% is entered as 18, while the equivalent decimal is 0.18. The calculator’s decimal output already includes the conversion.
• Using the wrong divisor: Dividing by 12 gives a monthly rate estimate, not a daily rate. Confirm whether the terms specify 360, 365, or another method.
• Rounding too soon: Keep the full rate in intermediate calculations. Rounding the daily percentage aggressively can change a multi-day estimate.
• Assuming a daily rate gives the final charge: The interest amount can depend on changing balances, transaction dates, payments, compounding, grace periods, and contract-specific rules, none of which this rate-only calculation models.

The result is therefore a mathematical conversion under the stated 365-day assumption, not a promise of the interest that will appear on an account statement. For actual amounts, use the rate and calculation method in the relevant disclosure or account terms.

Frequently Asked Questions

How do I calculate a daily periodic rate?
Divide the APR by the number of days specified by the applicable method. With a 365-day convention, daily periodic rate (%) = APR (%) ÷ 365.

What is the daily periodic rate for an 18% APR?
Using 365 days, 18% ÷ 365 is approximately 0.049315% per day, or 0.00049315 as a decimal.

Is the daily periodic rate the same as APR?
No. APR is an annual rate, while a daily periodic rate is the rate assigned to one day under a specified day-count convention.

Should I divide APR by 360 or 365?
Use the day-count method stated in the account or loan terms. This calculator uses 365 days; a 360-day divisor gives a different result.

How do I estimate one day of interest?
Multiply the balance subject to interest by the daily rate expressed as a decimal. The estimate may differ from a posted charge if the balance or calculation rules vary.

This result is an estimate, and the lender’s disclosure gives the exact figures.

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in apr | Annual percentage rate (APR) | % | 18 | 0.01 | 100
out daily | Daily periodic rate | % | apr / 365 | 6
out dec | Daily rate as a decimal | - | (apr / 365) / 100 | 8