Invoice generatorFree, no sign-up — your invoice is saved in your browser, not in an account

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 does not know it and does not guess.

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

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

What this calculator does not do

  • It does not know what you are entitled to charge, or whether you are entitled to charge anything. That depends on your contract and your jurisdiction, and in some places on whether the debt is commercial.
  • It does not add the fixed compensation some statutory schemes allow alongside interest, or any recovery costs. Those are separate amounts with their own rules.
  • It does not handle part payments. Interest here runs on one balance for the whole period; if they paid some of it halfway through, work out each stretch separately.
  • It does not 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

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, there is the invoice due date calculator.

Last updated 21 September 2026