Interest Per Day Calculator

Written by Great Medico

Updated September 27, 2026 •2 min read

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Interest can feel abstract when it is quoted as an annual percentage. The Interest Per Day Calculator converts an annual rate into a simple daily rate and estimates how much interest accrues each day on the balance you enter.

What this calculator does

Choose a currency, enter the current loan balance, and enter the annual interest rate. The calculator reports estimated interest per day and the equivalent daily percentage rate using a 365-day year.

How to use it

Use the principal or outstanding balance on which interest is actually being calculated. Enter the annual rate as a percentage—for example, enter 4 for 4%. The result is most useful for simple daily-accrual estimates and for seeing how balance changes affect daily interest.

Interest per day formula

The calculator uses daily rate = annual interest rate ÷ 365. The percentage is then converted to decimal form, and interest per day = loan balance × daily rate. This is a simple daily-interest model; it does not compound the daily interest back into the balance automatically.

Worked examples

With a $500,000 balance at 4% per year, annual simple interest is $20,000. Dividing by 365 gives about $54.79 per day. A $1,000,000 balance at the same rate produces about $109.59 per day.

How to interpret the result

The figure is an estimate of one day’s interest at the entered balance and annual rate. If the balance changes after payments, draws, capitalization, or fees, the next day’s interest may change as well. The daily percentage is simply the annual nominal percentage spread across 365 days in this model.

Limitations and practical notes

Actual lenders may use 360-day, 365-day, or actual-day conventions; compound interest; periodic rates; minimum-interest rules; or specific posting dates. Mortgages, credit cards, student loans, and commercial loans can each use different accrual methods. Check the loan agreement or lender statement when an exact payoff or contractual interest amount is required.