Daily Interest Calculator
Enter a balance and annual rate. See what one day of interest costs or earns — the number behind payoff quotes, per-diem loan interest, and savings accrual.
| Over 30 days | — |
| Per week | — |
| Per month (30 days) | — |
The daily interest formula
Daily interest = Balance × annual rate ÷ 365
$20,000 at 7% accrues $3.84 per day — $115 over 30 days. Loans typically accrue this way (simple daily interest on the remaining principal); savings accounts compound daily, which nudges the total slightly higher over longer periods.
Where the per-day number runs your life
- Loan payoff quotes: "good through" dates exist because the payoff grows by the daily interest — pay 10 days late and this example owes $38 more.
- Mortgage closings: prepaid per-diem interest from closing day to month-end is a standard line on the settlement sheet.
- Card grace periods: lose the grace period (by carrying a balance) and daily accrual starts on every purchase from day one.
- Motivation math: knowing your debt costs $3.84 every single morning reframes extra payments better than any annual percentage.
Note lenders' day-count conventions vary (365, 360, or actual/360 in commercial lending) — the 360-day year quietly charges ~1.4% more interest per year at the same stated rate.
Frequently asked questions
How do I calculate daily interest?
Balance × annual rate ÷ 365. $20,000 at 7% = $3.84 per day. Multiply by days for a period, or compound for savings accounts.
Why is my loan payoff amount different from my balance?
Payoff = balance + interest accrued since the last payment, plus interest through the payoff date. Quotes carry a good-through date because the number grows daily.
What is per diem interest at closing?
Mortgage interest from the closing date to month-end, prepaid at settlement: loan × rate ÷ 365 × remaining days. Closing late in the month minimizes it.
Do banks use 360 or 365 days?
Consumer loans and savings mostly use 365; commercial loans often use 360 (raising effective cost ~1.4%). The note or account agreement states the convention.
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Last updated: 2026-07-08