Late Payment Interest: Common Mistakes, Tips and FAQs

Introduction

Business and employment calculations are full of terms that sound alike but mean different things, such as margin and markup.

This article covers the most common mistakes people make with late Payment Interest, what really moves the result, and answers to the questions we hear most often.

Why it matters

Clear numbers help you price profitably, chase late invoices with confidence and understand statutory pay entitlements.

How it's calculated

Under the Late Payment of Commercial Debts Act you can charge 8% plus the Bank of England base rate per year, plus fixed compensation of £40, £70 or £100 depending on the debt size.

What changes the result most

We raised each input by 10% on its own, starting from a typical example where total you can claim is £119.32. Here's what happened:

• Raising invoice amount from £5,000 to £5,500 changes total you can claim to £124.25 (+4.1%).
• Raising days overdue from 30 to 33 changes total you can claim to £124.25 (+4.1%).
• Raising bank of England base rate from 4 % to 4.4 % changes total you can claim to £120.96 (+1.4%).

Focus first on invoice amount, which has the biggest effect in this example.

Common mistakes to avoid

1. Confusing margin and markup when setting prices.
2. Leaving VAT inside revenue figures when calculating profit.
3. Not claiming late payment compensation you're entitled to.
4. Using out-of-date statutory pay or minimum wage rates.

A quick example

With the inputs below, total you can claim comes out at £119.32.

Tips

• Price from margin, not markup, if you want to hit a target profit percentage.
• Quote prices to businesses ex VAT and to consumers inc VAT.
• You can legally claim statutory interest on late B2B invoices.
• Statutory pay rates usually change every April – check GOV.UK.

Frequently asked questions

What's the quickest way to work out late Payment Interest?

Use our free late Payment Interest Calculator. It applies this method automatically: Under the Late Payment of Commercial Debts Act you can charge 8% plus the Bank of England base rate per year, plus fixed compensation of £40, £70 or £100 depending on the debt size.

Are statutory pay figures up to date?

Rates are editable on each calculator. Defaults reflect recent published rates; always confirm current figures on GOV.UK.

Do these work for sole traders?

Yes. Margin, markup and break-even apply to any business size.

Is this legal advice?

No. For disputes about pay, redundancy or debts, contact Acas, Citizens Advice or a solicitor.

Related calculators

• Profit Margin Calculator
• Markup Calculator
• Break-Even Calculator
• ROI Calculator
• Discount Calculator
• Redundancy Pay Calculator

For the full method, read How to Calculate Late Payment Interest in the UK: Step-by-Step Guide.