APR Daily Interest Calculator
Calculate the daily periodic rate from an APR and the interest a credit-card balance accrues over a number of days, plus the ending balance.
How to use this tool
- Enter the balance interest is charged on.
- Enter the card's APR.
- Enter the number of days (e.g. a billing cycle).
- Read the daily rate, interest per day, period interest, and ending balance.
Convert an APR to a daily periodic rate and see the interest a balance accrues over any number of days. Enter the balance, APR, and the number of days.
Formula
Daily periodic rate (DPR) = APR ÷ 365
Interest per day = Balance × DPR
Interest over the period = Balance × DPR × Days
Ending balance = Balance + Period interest (this simple model does not compound daily).
How it works
Credit-card issuers usually quote an annual APR but actually charge interest on a daily basis. The daily periodic rate is the APR divided by the number of days in the year (365 here), and the interest charged is the balance times that daily rate, multiplied by the number of days in the period. This tool reports the daily rate, the dollars per day, the interest over your chosen window, and the resulting ending balance — handy for understanding a statement or estimating the cost of carrying a balance for a few extra days.
Two modelling notes. First, this uses simple daily interest on a fixed balance; many issuers compound daily by adding each day's interest to the balance, which makes the real figure marginally higher over long windows. Second, some issuers divide by 360 instead of 365 — change the days or read your agreement if you need an exact match. For a single billing cycle on a steady balance, the simple model is very close.
Reviewed by the AbraCalc Credit Desk. This is general information, not financial advice; confirm your card's terms (APR, fees, minimum-payment rule) with your issuer or a qualified advisor.
Worked example
$1,000 at 18.25% APR over 30 days
- Daily periodic rate = 18.25% ÷ 365 = 0.05%.
- Interest per day = 1,000 × 0.05% = 0.50.
- Interest over 30 days = 0.50 × 30 = 15.00.
- Ending balance = 1,000 + 15 = 1,015.
Interest over the period = $15.00 (daily rate 0.0500%, $0.50/day)
Daily periodic rate and 30-day interest on $1,000
| APR | Daily rate | Interest per day | 30-day interest |
|---|---|---|---|
| 12.00% | 0.0329% | $0.33 | $9.86 |
| 18.25% | 0.0500% | $0.50 | $15.00 |
| 21.90% | 0.0600% | $0.60 | $18.00 |
| 24.00% | 0.0658% | $0.66 | $19.73 |
| 29.99% | 0.0822% | $0.82 | $24.65 |
| 36.50% | 0.1000% | $1.00 | $30.00 |
Key terms
- Daily periodic rate (DPR)
- The APR divided by the number of days in the year (commonly 365); the rate applied each day.
- APR
- The annual percentage rate — the yearly interest rate the card quotes.
- Average daily balance
- The balance issuers often use for the period; this tool uses a single fixed balance for clarity.
- Daily compounding
- When each day's interest is added to the balance so the next day's interest is slightly higher.
Frequently asked questions
- How is the daily periodic rate calculated?
- Divide the APR by the number of days in the year. Most issuers use 365, so a 18.25% APR gives a daily rate of 0.05%. Some use 360, which is slightly higher.
- Does this account for daily compounding?
- No — it uses simple daily interest on a fixed balance. Issuers that compound daily add each day's interest to the balance, making the real charge marginally higher over long periods.
- Why do issuers charge interest daily?
- Daily accrual lets issuers charge interest based on your actual balance each day (often via an average daily balance), so paying down sooner reduces the interest you owe.