An overdue invoice costs you more than the money itself. It costs time spent chasing, cash flow shortfalls, and the awkward dynamic of pressing a client for something they already owe. Charging a late payment fee is one of the most effective tools available to freelancers and small businesses — but most do not use it because they are unsure how to set it up, what rate to use, and how to actually add it to an invoice.
This guide explains how late payment fees work, how to calculate the interest charge, how to include the clause in your payment terms, and how to issue a supplemental invoice when a client is overdue.
What is an invoice late fee?
A late payment fee — also called a late payment interest charge or finance charge — is an additional amount added to an invoice when the client pays after the agreed due date. It compensates the supplier for the cost of delayed payment: lost investment returns, bank charges, and the administrative burden of chasing.
Late fees can take two forms:
- Interest-based: a percentage of the outstanding amount per day, week, or month
- Fixed penalty: a flat fee triggered the moment the invoice becomes overdue
In practice, most professional invoicing uses interest-based charges, sometimes combined with a fixed administrative penalty.
Legal framework: what rates apply?
The applicable rate depends on the country. Here is an overview of the main jurisdictions:
United Kingdom
The Late Payment of Commercial Debts (Interest) Act 1998 gives businesses the statutory right to charge interest on overdue B2B invoices at 8% above the Bank of England base rate. As of June 2026, with the base rate at approximately 4.25%, the statutory rate is around 12.25% per annum.
In addition, businesses can claim a fixed debt recovery compensation:
- £40 for debts up to £999.99
- £70 for debts between £1,000 and £9,999.99
- £100 for debts of £10,000 or more
This statutory right applies automatically, even if you did not include a specific late fee clause — provided the transaction is B2B.
European Union
EU Directive 2011/7/EU on combating late payment requires member states to allow businesses to charge interest at the European Central Bank reference rate plus 8 percentage points (10%+ in most years) for commercial transactions. Most EU countries have implemented this minimum rate, and many allow higher contractual rates.
United States
There is no federal late payment rate for commercial invoices. Most states allow contractual late fees between 1.5% and 3% per month (18% to 36% annually), provided the rate is disclosed in the contract or invoice terms. Some states cap the maximum rate, so check your state laws.
Contractual vs statutory rates
You can always agree on a contractual rate with the client — higher or lower than the statutory rate — provided you include the clause in your terms and conditions or on the invoice itself before the work begins. If no rate is specified, the statutory rate typically applies by default in the UK and EU.
How to calculate a late payment interest charge
The formula for interest-based late fees is straightforward:
Interest = Outstanding amount × Annual rate ÷ 365 × Number of days overdue
Example
- Invoice amount: £2,500
- Annual rate: 12.25% (UK statutory, June 2026)
- Days overdue: 45
Calculation:
£2,500 × 0.1225 ÷ 365 × 45 = £37.84
If you also apply the statutory UK debt recovery compensation of £70 (for a debt between £1,000 and £9,999.99), the total additional charge is:
£37.84 + £70.00 = £107.84
You would issue a supplemental invoice for £107.84, clearly referencing the original overdue invoice.
How to include a late fee clause in your payment terms
The most effective way to charge late fees is to include the clause before any dispute arises — ideally in your contract, your terms and conditions, and on every invoice.
On the invoice itself
Most professional invoices include a line at the bottom of the payment terms section:
"Invoices unpaid after [due date] will incur late payment interest at [rate]% per annum ([rate ÷ 12]% per month) under the Late Payment of Commercial Debts (Interest) Act 1998, plus a statutory debt recovery fee of £[amount]."
If you are in the EU:
"In accordance with Directive 2011/7/EU, overdue amounts will accrue interest at the ECB reference rate plus 8 percentage points from the due date."
For a US-based business:
"A late payment fee of 1.5% per month will be applied to all balances unpaid after the due date."
In your contract or terms and conditions
Your signed contract or general terms should include a dedicated clause covering:
- The due date (or payment period, e.g. 30 days from invoice date)
- The applicable interest rate and how it accrues
- Any fixed debt recovery fee
- The currency in which charges will be calculated
Without this clause, enforcing a late fee against a reluctant client becomes significantly harder.
How to write a late fee invoice
When a client is overdue and you want to formalise the interest charge, you issue a supplemental invoice specifically for the late payment fee. This is separate from the original invoice.
The supplemental invoice should include:
- A unique invoice number (from your own sequential series)
- The date of issue
- Reference to the original overdue invoice (number and amount)
- The period of delay (from the due date to the date of the supplemental invoice)
- The interest rate used
- The calculation showing how the amount was reached
- The fixed penalty if applicable
- The total amount due
Sample supplemental invoice text
INVOICE — LATE PAYMENT INTEREST CHARGE
Invoice number: INV-2026-057
Date: 2 June 2026
Reference: Original invoice INV-2026-031 (issued 1 April 2026, due 1 May 2026)
Late payment interest:
£2,500 × 12.25% ÷ 365 × 32 days overdue = £26.92
Statutory debt recovery compensation (UK): £40.00
Total due: £66.92
Payment terms: Due immediately on receipt
Does late fee income count as taxable revenue?
Yes. In most jurisdictions, interest and late fees received from clients are treated as business income and are subject to the same tax treatment as your primary income. You should include them in your accounts and declare them accordingly.
For VAT purposes, late payment interest is generally outside the scope of VAT in the UK and EU — it is financial compensation, not a supply of goods or services. However, a fixed admin fee charged as part of a service supply might be treated differently. If in doubt, consult your accountant.
Common mistakes when charging late fees
Not disclosing the rate upfront
A late fee clause you invent after the invoice is overdue will not hold up legally. The rate must be agreed before the transaction. If it is not in your contract or on your invoice, the client can legitimately dispute the charge.
Applying fees to consumer invoices without checking local rules
In most jurisdictions, the statutory late payment legislation applies to B2B transactions only. Different rules apply when invoicing consumers (B2C), and excessive consumer charges may be unenforceable or even illegal.
Charging compound interest without disclosure
Simple interest is standard. Compound interest (interest on interest) must be explicitly agreed in advance and is unusual in commercial invoicing.
Letting overdue balances accumulate too long
A late fee is a tool, not a collection strategy. If an invoice is seriously overdue, the practical priority is recovering the original amount. See our guide on what to do when an invoice is unpaid for a full escalation process.
Should you always charge a late fee?
Legally, yes, you are entitled to. Practically, the answer depends on context.
For long-term clients who rarely pay late, a quiet reminder is often enough, and charging a small fee risks damaging a valuable relationship. For new clients, late-paying clients, or large overdue amounts, charging the fee sends a clear signal that your payment terms are serious — and that there is a cost to ignoring them.
Many freelancers find that simply mentioning their late fee clause during the initial project discussion significantly improves payment behaviour, even if the fee is never actually applied.
Setting payment terms to reduce late payments
The most effective late fee is one you never need to issue. Some practical steps:
- Issue invoices immediately upon completion, not days or weeks later
- Use a specific due date rather than "net 30" or "within 30 days"
- Send a proactive reminder a few days before the due date
- Accept multiple payment methods (bank transfer, card, online payment)
- For larger projects, consider staged payments with partial invoices
For guidance on structuring payment terms effectively, see our article on invoice payment terms.
Summary
Charging a late payment fee is a legitimate and often legally automatic right in most countries. The key steps are: set the clause in your payment terms before the work starts, calculate the interest correctly using the applicable rate and the exact number of days overdue, and issue a separate supplemental invoice clearly referencing the original debt.
Invoice Creator helps you generate clean, professional invoices with your payment terms already included, and makes it easy to issue supplemental invoices for late fees when they arise. For ready-made invoice structures, use the invoice templates library.