Simple Interest Calculator for Invoices

Calculate simple interest on overdue invoices quickly. Enter the invoice amount, annual rate, and dates to get interest and total due.

Why simple interest?

Many invoice agreements apply a simple annual rate over the overdue period. This page focuses on the simple interest method (no compounding).

Amount owed

Annual interest rate (%)

Start date

End date

Currency

Formula: Interest = Amount × Rate × (Days/365). Verify your contract or statutory rules for the correct rate.

Days overdue

—

Interest

—

Total

—

How it’s calculated

—

No. This page calculates simple interest only. If you need daily compounding, use the Daily Compound page.

No. This tool provides an estimate only.