Daily Periodic Rate Calculator and Formula

A daily periodic rate is the interest rate applied to a balance for one day; this calculator estimates it by dividing an annual percentage rate (APR) by the number of days in the year used for the calculation. Enter an APR and choose a 360- or 365-day basis to see the daily rate and the estimated interest on a balance for one day.

Formula

Daily periodic rate = annual percentage rate ÷ days in the rate year. The output is expressed as a percentage per day.

• APR is the annual percentage rate entered as a percent, such as 18 for 18%.
• Days is the divisor used by the account’s calculation, typically 360 or 365. This calculator permits those two common conventions.
• Balance is the dollar amount on which one day of interest is estimated.
• Daily interest is balance × APR ÷ (100 × days), in dollars, before any account-specific rounding or adjustments.

For example, an APR of 18% divided by 365 gives a daily periodic rate of about 0.049315% per day. In decimal form, that is 0.00049315 per day. The percentage and decimal forms describe the same rate: divide the percentage figure by 100 to convert it to a decimal.

Worked Example

Using the calculator’s defaults—APR 18%, 365 days, and a $1,000 balance:

1. Daily periodic rate = 18 ÷ 365 = 0.049315% per day, rounded to six decimal places.
2. Convert the APR percentage to a decimal and divide by 365: 0.18 ÷ 365 = 0.0004931507 per day.
3. One-day interest = $1,000 × 18 ÷ (100 × 365) = $0.4931507, which rounds to $0.49 to the nearest cent.

The displayed rate is rounded for readability. The interest estimate is calculated from the unrounded inputs, not by multiplying the rounded six-decimal rate.

How Daily Periodic Rates Work

A periodic rate is the portion of an annual rate assigned to a shorter period. For an account using a daily rate, the issuer or lender may apply that rate to a balance for each day in the billing or accrual period. A simplified daily interest calculation is balance × daily rate, with the daily rate written as a decimal.

Actual account calculations can involve more than one daily multiplication. For example, a revolving balance may change when purchases, payments, credits, or fees post. An account may calculate interest each day on that day’s balance, then add or otherwise account for accrued interest according to its terms. Consequently, the one-day figure here is an illustration, not a prediction of a statement’s final interest charge.

Some disclosures describe a daily periodic rate directly. Others show an APR and explain the daily-rate convention. Use the rate and method stated in the relevant account disclosure rather than assuming the calculator’s divisor matches a particular product.

Choosing 360 or 365 Days

The divisor matters because the same APR produces a slightly different daily rate with different day counts. Dividing by 360 yields a higher daily rate than dividing by 365. The calculator includes both options because financial agreements may specify different conventions; it does not decide which convention applies to an account.

• Choose 360 if the governing terms say the daily rate uses a 360-day year.
• Choose 365 if the terms specify a 365-day year.
• If the disclosure states a daily periodic rate, use that disclosed figure when assessing the account; a rounded APR conversion may not reproduce it exactly.

A leap year does not automatically mean that the divisor is 366. The relevant basis is whatever the agreement or disclosed calculation method specifies. Check the terms if they do not clearly state the day-count convention.

Using the Result and Common Errors

The daily periodic rate is useful for understanding how an annual rate is scaled to a daily period. The one-day interest output shows the approximate dollar effect on the entered balance for one day, before transaction timing, compounding details, and account-specific rounding.

• Entering 18 instead of 0.18: The APR input is a percentage, so enter 18 for 18%, not 0.18.
• Confusing percentage with decimal: A displayed rate of 0.049315% equals about 0.00049315 as a decimal. Multiplying a balance by 0.049315 directly would overstate the result by a factor of 100.
• Using a convenient but incorrect divisor: Do not pick 360 or 365 without checking the applicable terms.
• Rounding too early: Multiplying by the displayed rounded daily rate can create small differences. Keep more precision during intermediate steps and round money only at the end for an estimate.
• Assuming the balance stays fixed: Daily balances can change as transactions post, so one day’s interest cannot usually be multiplied by the number of days to reproduce an entire bill.

Daily Rate Compared With APR and Periodic Interest

APR is an annualized rate shown as a percentage per year. A daily periodic rate expresses a rate for one day. The simple conversion in this calculator divides the APR by a stated day count; it is not a separate fee and should not be confused with the total interest charged over a year.

Periodic rates can also be monthly or tied to another interval. A monthly periodic rate is not obtained by dividing by 30 unless the account’s method says so. Nor does a daily rate by itself tell you the total cost of borrowing: that depends on the balance over time, payment and posting dates, compounding method, and the agreement’s other terms.

Limits of This Estimate

This tool applies a straightforward APR-to-daily-rate conversion and estimates interest for one unchanged balance over one day. It does not calculate a statement balance, a multi-day average daily balance, compound interest, payment allocation, grace-period treatment, fees, or any special account rules. It also does not infer whether an APR includes particular charges or how an account handles rounding.

For a statement reconciliation, use the account’s disclosed rate, day-count basis, balance method, transaction dates, and rounding rules. The result is an estimate, and the lender’s disclosure gives the exact figures.

Frequently Asked Questions

How do you calculate a daily periodic rate?
Divide the APR percentage by the number of days specified for the rate year. For example, 18% ÷ 365 is approximately 0.049315% per day.

Is a daily periodic rate the same as APR?
No. APR is an annualized percentage; a daily periodic rate is the rate assigned to a day under a stated calculation convention.

Should I divide APR by 360 or 365?
Use the divisor specified in the account agreement or disclosure. The calculator shows both conventions but cannot determine which one applies to your account.

How do I estimate one day of interest?
Convert APR to a decimal, divide by the day-count basis, then multiply by the balance. For a percentage APR, the equivalent expression is balance × APR ÷ (100 × days).

Why does my statement’s interest differ from this result?
A statement may reflect changing daily balances, transaction timing, multiple balances or rates, compounding, and rounding rules. This calculator estimates interest on one fixed balance for one day only.

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in apr | Annual percentage rate (APR) | % | 18 | 0.01 | 100
in days | Days in rate year | days | 365 | 360 | 365
in bal | Balance | $ | 1000 | 0 | 100000000
out dpr | Daily periodic rate | % | apr / days | 6
out int | One-day interest | $ | bal * apr / (100 * days) | 2