Late payment interest calculator
See simple interest on an overdue amount from the rate and dates you type.
Result
Late payment interest calculator
Interest
—
Enter the amount, the rate, the due date and the as-of date.
Ballpark estimate, check before you buy or quote.
Rates as of 2026-10-03, tax year 2026. This is a simple estimate, not advice. It is not a fee you can add unless your own agreement says so.
Estimate for planning only. This is not tax, legal, accounting or financial advice. Results depend on the figures you enter. Check all numbers, rates and rules with the official source or a qualified professional before relying on them.
How this works and common questions
About this tool
Interest is simple, not compounded, from the annual rate and the dates you type. This is a simple estimate, not advice. It is not a fee you can add unless your own agreement says so.
How it works
Days overdue are the as-of date minus the due date. Interest is the amount times the annual rate you type times those days, divided by 365, rounded half away from zero to the cent. It is not compounded.
Rules
Rates as of 2026-10-03, tax year 2026. This is a simple estimate, not advice. It is not a fee you can add unless your own agreement says so. You type the rate. The year is 365 days. Nothing is stored.
Questions
How is the interest calculated?
Simple interest: amount times the annual rate you type times the days overdue, divided by 365, rounded half away from zero to the cent. $1,000.00 at 12% for 30 days is $9.86.
What if the as-of date is before the due date?
Days overdue are 0 and interest is $0.00. The page does not treat that as a credit.
Can I add this to an invoice?
Only if your own agreement says so. This page does not state a legal rate or a right to charge interest.
Do I need an account?
No. The tools work without one. You only need to sign in to save your work.
Is what I type saved?
No. Nothing is saved unless you sign in and choose Save. Otherwise it stays on the page.
Do you show ads or sell my information?
No. We show no ads and we do not sell your information.
Is this tax or legal advice?
No. Results are estimates for planning. Check rates and rules with the official source or a qualified professional.
Sign in to save this. Your entries stay on screen.
Estimate for planning only. This is not tax, legal, accounting or financial advice. Results depend on the figures you enter. Check all numbers, rates and rules with the official source or a qualified professional before relying on them.