Calculate interest that accumulates daily on loans or savings with this fast Daily Interest Calculator.
| Day | Date | Opening Balance | Daily Interest | Closing Balance |
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Type the opening balance and the annual interest rate (APR). Choose your currency and whether to use simple or compound interest.
Enter a number of days directly, or switch to date mode and pick a start and end date. The calculator counts the exact number of days automatically.
See your per diem rate, weekly and monthly interest, total interest for the period, and ending balance — all updating live as you type.
Download a day-by-day CSV accrual schedule, print a clean PDF report, or copy all results to clipboard for records or further analysis.
Per diem rate, weekly, monthly, and total interest all update instantly as you type — no need to press a button or reload the page.
Switch from entering days manually to picking exact start and end dates. The calculator counts calendar days automatically — including leap years.
Choose between simple interest, daily compound, or monthly compound accrual. See how compounding frequency affects your total interest cost or earnings.
Supports Actual/365 (most common), Actual/360 (US bank loans), and 30/360 (bond markets) — the right basis for every financial context.
All calculations run entirely in your browser. No data is ever sent to a server, stored, or tracked — your financial figures stay completely private.
Toggle on a full per-day accrual table showing each day's opening balance, interest charge, and running total — perfect for audits and reconciliations.
Fully responsive design works perfectly on desktop, tablet, and mobile. Calculate your per diem anywhere — in the office, courtroom, or on the go.
Download results as a CSV for spreadsheets, print a clean PDF report, or copy everything to clipboard to paste into an email or document.
Daily interest (also called per diem interest) is the amount of interest that accrues on a balance in a single calendar day. It is calculated by dividing the annual interest rate by the number of days in the year and multiplying by the outstanding balance.
The standard formula is Daily Interest = Balance × (APR ÷ Day Basis). Most lenders use an Actual/365 or Actual/360 basis. Over multiple days, interest accumulates — and with compound interest, each day's interest is added to the principal before the next day's calculation.
The per diem ("per day") interest rate is simply APR ÷ 365. On a $10,000 balance at 5% APR, you accrue $1.37 every single day — including weekends and holidays.
Lenders using an Actual/360 basis divide by 360 instead of 365, making the effective interest rate about 1.39% higher than the stated APR — a meaningful difference on large balances.
With simple daily interest, the rate always applies to the original balance. With compound daily interest, today's interest is added to the principal before tomorrow's calculation — accelerating accrual over time.
When you request a mortgage payoff amount, your lender calculates the outstanding balance plus per diem interest through the payoff date. Closing a day late means one more day of interest on the full remaining balance.
Credit card issuers typically use daily periodic rate (DPR) = APR ÷ 365. They multiply this by your average daily balance for the billing cycle to calculate the interest charge that appears on your statement.
Paying off a loan even one week early reduces the total interest by 7× the daily interest rate. On a $200,000 mortgage at 7%, that's about $38 saved per day — nearly $1,150 saved if you pay a month early.
Calculate simple interest on loans and savings to understand basic interest calculations.
Calculate compound interest growth on savings or investments with regular contributions.
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Free, instant, and accurate no account required. Run your first calculation in under 10 seconds.
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