Use this free daily interest calculator to find how much interest a balance earns or costs each day, also called per diem interest. It’s useful for mortgage and auto loan payoffs, savings accounts, late payments, and any time you need interest for a specific number of days.
Count days between dates, and day-count basis
Pick both dates and the calculator fills in the number of days for you.
Most U.S. mortgages and savings accounts use 365. Some commercial loans and payoff quotes use 360, which makes each day’s interest a little higher.
Interest per day
$44.52
- Starting balance—
- Interest—
- Balance plus interest—
How interest adds up
Simple daily interest = balance × (annual rate ÷ days in year) × days. Compounded daily adds each day’s interest to the balance. Assumes a fixed rate and no payments or deposits during the period. Estimates for educational use, not financial advice.
How to Use This Daily Interest Calculator
- Choose simple or compounded. Pick Simple daily interest for loan payoffs and per diem quotes. Pick Compounded daily for savings accounts that add interest to your balance every day.
- Enter the balance and annual rate. For a loan, use the current principal balance and the interest rate on your statement.
- Set the number of days. Tap a common period, type any number, or open Count days between dates and pick a start and end date.
- Check the day-count basis. Most U.S. mortgages and deposit accounts divide the annual rate by 365. Some lenders and government payments use 360.
Daily Interest Formula
For simple daily interest, first find the daily rate, then multiply by the balance and the number of days:
Daily interest = Balance × (Annual rate ÷ 365) Interest for a period = Daily interest × Number of days
For interest compounded daily, each day’s interest is added to the balance before the next day’s interest is calculated:
Interest = Balance × [(1 + Annual rate ÷ 365)days − 1]
Daily Interest Examples
Example 1: Mortgage payoff (per diem)
You owe $250,000 on a mortgage at 6.50%. The daily interest is $250,000 × (0.065 ÷ 365) = $44.52 per day. If your payoff happens 15 days after your last payment, about $667.81 of interest will be added to your payoff amount. On a 360-day basis, the same loan would accrue $45.14 a day, or $677.08 over 15 days.
Example 2: Savings compounded daily
You keep $10,000 in a savings account paying 5.00%, compounded daily. After 365 days, you earn about $512.67, compared with $500.00 using simple interest. That extra $12.67 is the effect of compounding. Use our APY calculator to compare accounts that compound on different schedules.
What Is Per Diem Interest?
“Per diem” means “per day.” Per diem interest is the interest that builds up each day on a loan. You’ll see it in a few common places:
- Paying off a mortgage or auto loan. Your payoff amount is usually higher than your current balance because it includes interest through the day the lender receives your payment. A payoff statement shows the exact amount and often the per diem figure for later dates.
- Closing on a home. At closing, buyers often prepay interest from the closing date to the end of the month. That prepaid interest is calculated per day.
- Late payments. Some contracts charge interest for each day a payment is late. Federal agencies, for example, pay interest on late invoices using simple daily interest on a 360-day year under the Prompt Payment Act.
365-Day vs. 360-Day Interest
| 365-day year | 360-day year | |
|---|---|---|
| Daily rate at 6.50% | 0.01781% | 0.01806% |
| Daily interest on $250,000 | $44.52 | $45.14 |
| Where you’ll see it | Most mortgages, savings accounts, credit cards | Some commercial loans, payoff quotes, government late payments |
Dividing by 360 creates a slightly higher daily rate, so the borrower pays a bit more over a full year. Your loan documents say which method your lender uses.
Frequently Asked Questions
How do I calculate daily interest on a loan?
Multiply the principal balance by the annual interest rate, then divide by 365 (or 360 if your lender uses that). For $20,000 at 7%, that’s $20,000 × 0.07 ÷ 365 = about $3.84 a day.
Why is my loan payoff amount higher than my balance?
Your balance doesn’t include interest that has built up since your last payment. The payoff amount adds interest through the day you plan to pay, plus any fees. Ask your lender for a payoff statement for an exact figure.
Does daily compounding earn much more than monthly?
Only a little. At 5.00%, daily compounding earns about $512.67 a year on $10,000, while monthly compounding earns about $511.62. The rate matters far more than the compounding schedule.
How do I find the number of days between two dates?
Open Count days between dates in the calculator and pick a start and end date. The calculator counts the days for you and updates the interest.
More free calculators
Sources
- Consumer Financial Protection Bureau: What is a payoff amount?
- Bureau of the Fiscal Service (U.S. Treasury): Prompt Payment interest calculation
- Consumer Financial Protection Bureau: What is a daily periodic rate?
This calculator provides estimates for educational purposes only and is not financial advice. Your lender’s payoff statement is the official amount owed. Last updated: October 12, 2026.