Free Invoice Generator

Late payment interest calculator

Work out what an overdue invoice has accrued at an annual rate, simple or compounded, and what one more day of waiting adds to it.

The unpaid invoice

What is still unpaid. Interest runs on this, not on the total invoiced.

Used only if you press Create this invoice, as the name of the balance line.

How long it has been outstanding

Interest runs from the day after this one. The due date calculator works it out from your terms.

Today, or the day you expect to be paid.

The rate

The rate your contract sets, or the statutory one where you invoice. This page doesn't know it and doesn't guess.

Statutory interest is normally simple. Use compound only if the agreement says so.

GuideLate payment interestHow this works, and where the figures go wrong →

What the late payment interest calculator does not do

  • It doesn't know whether you're entitled to charge interest. That depends on your contract and your jurisdiction, and in some places on whether the debt is commercial. The rate you enter is yours to check.
  • It adds interest and nothing else. Some statutory schemes allow fixed compensation or recovery costs alongside interest. Those are separate amounts with their own rules, and they aren't included here.
  • It assumes one balance for the whole period. If the client paid part of it halfway through, work out each stretch separately and add them up.
  • It doesn't keep anything. Nothing is written to your browser's storage while you use it and nothing is sent to us, so the figures are gone when you close the tab.

Related

To find the statutory rate where you invoice, late payment laws by country gives the formula for each country and links to the current figure. For a flat or one-off late charge rather than interest running daily, use the late payment fee calculator. To work out the due date this page counts from, use the invoice due date calculator. To put the interest in a formal reminder, the payment reminder email generator works it out the same way and writes the email around it. If the formal reminder's date passes too, the final notice letter generator puts the interest, and the fixed sum the UK and EU schemes add, into the last letter before you hand the debt on.

Last updated 21 September 2026