How to Write an Invoice: A Step-by-Step Guide for UK Businesses
Whether you're a freelancer, sole trader, or limited company, knowing how to write a proper invoice is essential. A well-structured invoice not only looks professional — it ensures you get paid correctly and on time.
This guide walks you through everything you need to include on a UK invoice, step by step.
What Is an Invoice?
An invoice is a formal document you send to a client requesting payment for goods or services. It's a legal record of the transaction and is essential for your accounting records.
In the UK, there is no single mandatory invoice format — but HMRC has clear expectations about what should be included, especially if you're VAT-registered.
What to Include on a UK Invoice
1. The word "Invoice"
Always label the document clearly as an invoice. This sounds obvious, but it matters for legal and accounting purposes.
2. A unique invoice number
Every invoice should have a unique, sequential reference number. This helps you track outstanding payments and makes it easy to reference in any disputes.
Example: INV-001, INV-2026-042
3. Your business details
Include:
- Your full name or business name
- Your address
- Your contact email or phone number
- If you're VAT-registered: your VAT registration number
4. Your client's details
Include:
- The client's name or company name
- Their address
5. Invoice date
The date the invoice was issued. This is also your reference point for calculating payment due dates.
6. Payment due date
Clearly state when payment is due. In the UK, the standard is 30 days unless otherwise agreed. You can use:
- "Payment due within 30 days"
- "Due by 6 May 2026"
Under the Late Payment of Commercial Debts Act 1998, if you're a small business invoicing another business, you're legally entitled to charge interest on late payments.
7. Description of goods or services
Be specific. List each product or service separately with:
- A clear description
- Quantity
- Unit price
Vague descriptions slow down payment and can lead to disputes.
8. Subtotal, VAT (if applicable), and total
- Show the subtotal before tax
- If you're VAT-registered, show the VAT amount separately (e.g. 20% standard rate)
- Show the total amount due
9. Payment method and bank details
Tell your client how to pay. Include:
- Bank name
- Account name
- Sort code and account number
- Any reference they should use (e.g. your invoice number)
If you use PayPal or Stripe, include those details instead or as an alternative.
Do You Need to Include VAT?
Only if you're VAT-registered. You must register for VAT if your taxable turnover exceeds £90,000 in a 12-month rolling period (as of 2026).
If you are VAT-registered, you must issue a VAT invoice that includes:
- Your VAT registration number
- The VAT rate charged
- The VAT amount
If you're not VAT-registered, do not add VAT to your invoices.
Invoice Example
INVOICE
Invoice number: INV-2026-042
Date: 6 April 2026
Due date: 6 May 2026
From:
Jane Smith Freelance Design
123 Studio Lane, London, EC1A 1BB
jane@designbysmith.co.uk
To:
Acme Ltd
456 Business Park, Manchester, M1 2AB
Services:
Website redesign — April 2026 £1,500.00
Subtotal: £1,500.00
VAT (20%): £300.00
Total due: £1,800.00
Payment: BACS
Account name: Jane Smith
Sort code: 12-34-56
Account: 78901234
Reference: INV-2026-042
Thank you for your business.
Common Invoice Mistakes to Avoid
- Missing contact details — makes it hard for clients to raise queries
- No payment due date — clients may delay indefinitely
- No bank details — causes unnecessary back-and-forth
- Inconsistent invoice numbers — creates confusion in your records
- Vague descriptions — "Consultancy work" is less clear than "Brand strategy session, 3 hours @ £100/hr"
The Fastest Way to Write a UK Invoice
Writing invoices from scratch is time-consuming. Billdrop lets you create a professional UK invoice in under two minutes — no account needed, free PDF download.
It automatically handles:
- Sequential invoice numbering
- VAT calculations
- Multiple currencies
- Discounts and line items
- Instant PDF export