How to use
- Enter the balance the interest is charged on.
- Enter the annual rate as a percent.
- Enter the number of days.
- Press Calculate. The hero is the interest for that span.
How it's calculated
Interest = principal × (APR ÷ 100) ÷ 365 × days.
A note that uses a 360-day year will not match. Divide by 360 yourself if that is the contract. This page is fixed at 365 and says so in the result.
Worked example
Ten thousand dollars at 6 percent for 15 days: 10,000 × 0.06 ÷ 365 × 15 = $24.66. The same principal for 365 days is $600, which is the simple-interest result for one year.
Assumptions
One rate, one principal, and a 365-day year. No compounding and no fees. The display rounds to the cent.
FAQ
Why 365 and not 360?
365 is the count this page uses. Bank notes sometimes use 360. If yours does, the result here will be a little low.
Does the balance grow each day?
No. The principal stays the number you typed. Compound interest is a different calculator.
Is this the interest-only mortgage payment?
No. Interest-only on this site is one month, using APR divided by 12. This page is a count of days.
Can days be a fraction?
Yes. A day and a half is 1.5 if that matches the note.