Late Fee Calculator

An invoice is past due. Find out exactly how late it is, how much interest and late fees you're entitled to, and the updated total to put in your next email.

Overdue invoice details

Total now owed

$2,586.99

45 days past due

Original invoice$2,500
Interest accrued$37
Flat late fees$50
Months (or part) late2

How late fees are calculated

This calculator uses simple interest, the standard method for late payment charges:

Interest = Amount × Annual rate × (Days late ÷ 365)

Flat fees = Fee per month × complete months (or part) late

A $2,500 invoice that is 45 days overdue at 12% per year with a $25 monthly late fee accrues $2,500 × 0.12 × (45 ÷ 365) = $36.99 of interest, plus two months of flat fees ($50) — a new total of $2,586.99. Small numbers, but they change the tone of a collection email from annoyed to matter-of-fact.

Make sure you can actually charge it

Late fees hold up best when they were agreed before the work started. Three layers of protection, strongest first:

  1. A contract clause: "Invoices not paid within X days of the due date accrue interest at Y% per year plus a $Z monthly administration fee."
  2. A note on the invoice: repeat the terms on every invoice, next to the due date.
  3. Statutory rights: even without a clause, many places give business creditors automatic interest on late payments. The UK's Late Payment of Commercial Debts (Interest) Act sets 8% above the Bank of England base rate; the EU's Late Payment Directive applies similar defaults for business-to-business debts. Check your jurisdiction.

How to actually collect

Escalate politely and in writing. Send a reminder the day after the due date, a firmer email at 14 days that mentions the accumulating fees, and a final notice before involving a collections service or small-claims court. Keep every email dated — a paper trail of the invoice with a clear due date plus your reminders is usually all a small-claims process needs.

Prevention beats collection: deposits (30–50% upfront), shorter payment terms for new clients, and milestone billing all shrink the amount a late client can hold hostage.

Frequently asked questions

Can I legally charge a late fee on an overdue invoice?

Usually yes, if the fee was agreed in advance — in your contract or on the invoice itself. Many jurisdictions also give you a statutory right to interest on late commercial payments even without a written clause (for example, the UK's Late Payment of Commercial Debts Act and the EU's Late Payment Directive). Check local rules and your contract before demanding a specific amount.

What is a typical late fee for freelancers?

Two common structures: an annual interest rate on the outstanding amount (1–2% per month, i.e. 12–24% per year), or a flat fee per late month (commonly $25–$50). Many freelancers combine both. Whatever you choose, state it on the invoice or in the contract before the work starts.

How is late payment interest calculated?

Simple interest is the standard approach: outstanding amount × annual rate × (days late ÷ 365). For example, $2,500 overdue for 45 days at 12% per year accrues $2,500 × 0.12 × 45/365 = $37 in interest.

My invoice has no due date — is it still late?

Without a due date there is no clean definition of late, which is exactly why every invoice needs one. As a fallback, many jurisdictions treat payment as due within 30 days of receipt by default. Going forward, always put an explicit due date on your invoices — our invoice generator adds one automatically.

Get paid on time

The rest of the billing workflow:

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Invoice Generator

Next invoice: add a due date and late-fee terms so this doesn't recur.

Create an invoice → 🇬🇧

UK Statutory Calculator

In the UK? Claim 8% + base rate interest and £40–£100 fixed compensation by law.

Claim statutory interest → 📦

Project Rate Calculator

Next project: take a deposit and price it properly upfront.

Price a project →

Last updated: September 2026. The calculator runs entirely in your browser — your numbers never leave your device. This tool does not constitute legal advice.