Interest Per Day Calculator

Formula

Simple daily interest = principal × annual rate ÷ 100 ÷ 365.

Worked example

With Principal balance: 10000 currency units, Nominal annual rate: 6 %, simple interest per day is 1.64 currency units.

Inputs and calculation

Convert the quoted annual percentage to a decimal, multiply by the unchanged principal, then divide one year's simple interest across 365 equal days. Thirty days are shown as a linear extension. The displayed relationship is Simple daily interest = principal × annual rate ÷ 100 ÷ 365. Keep the fields' displayed units attached when reproducing this relationship by hand.

Worked numerical example

For example, enter principal balance 10,000 currency units, nominal annual rate 6 %. Those inputs produce simple interest per day of 1.6438 currency units. The same values also give simple interest over 30 days 49.3151 currency units.

Holding the other example values fixed, change principal balance from 10,000 to 11,000 currency units. The main output becomes 1.8082 currency units. This comparison isolates the effect of that one input.

How to read and use the result

The daily amount is a planning estimate on a fixed balance. It is not a lender statement or a prediction of what a compounding account will charge. Estimate the order of magnitude of daily interest on a debt or deposit.

Practical context

With 10,000 outstanding at a nominal 6% yearly rate on a 365-day basis, simple daily interest is about 1.64. Holding that principal unchanged for thirty days gives about 49.32.

Assumptions and scope

The model uses a 365-day basis and no payments, capitalization, changing rate or fees. Some agreements use actual days, 360-day conventions, average daily balances or compounding. Replace the example defaults with measured inputs for your situation and account separately for factors outside these fields.

Checks and common mistakes

Check the contract's accrual convention before reconciling a bill. Multiplying one day's figure by an entire month is inaccurate if the principal changes after each payment.

Common questions

What should I verify before using the Interest Per Day Calculator result?

If a payment lowers the balance after ten days, the last twenty days accrue on a smaller principal and the thirty-day shortcut overstates the actual amount. Credit-card issuers may use a 360-day divisor and daily compounding, while a loan contract may use a different accrual rule. Match the contract before reconciling cents.

Sources and references

• CFPB: Daily periodic interest rates