How to write an invoice (UK guide)

If you're freelancing or running a small business in the UK, getting your invoices right isn't optional — it's a legal requirement. A properly written invoice makes sure you get paid on time, keeps HMRC happy, and protects you if there's ever a dispute.

Here's exactly what to include, what the rules are, and how to avoid the mistakes that delay payment.

What must appear on a UK invoice

HMRC doesn't mandate a specific format, but every invoice you send should include these details:

• Your business name and contact details — name (or trading name), address, phone number, email
• Your client's name and address
• A unique invoice number — sequential, no gaps (INV-001, INV-002, etc.)
• The invoice date — the date you issue it
• A description of the goods or services — clear enough that your client knows exactly what they're paying for
• The amount due — unit price, quantity, and total for each line item
• The total amount — including any applicable VAT
• Payment terms — when you expect to be paid (e.g., "Net 30" means within 30 days)
• Your payment details — bank account, sort code, or a payment link

If you're VAT-registered, you must also include your VAT number and show VAT separately from the net amount. See our guide on UK VAT invoice requirements for full details.

Invoice numbering rules

HMRC requires invoice numbers to be unique and sequential. You can use any format — INV-001, 2026-001, or ACME-0001 — as long as there are no duplicates and no missing numbers in the sequence.

Why this matters: if you're ever audited, HMRC will check your invoice numbering for gaps. A gap suggests a missing invoice, which suggests unreported income.

Coinvoice assigns invoice numbers automatically using your chosen prefix, so you never have to track this manually.

What to write in the description

Vague descriptions cause payment delays. "Consulting services" tells your client nothing. Be specific:

Bad: "Design work — £500"

Good: "Website redesign for acme.co.uk — homepage layout, 3 inner page templates, mobile responsive. Delivered 15 March 2026 — £500"

The more specific your description, the harder it is for a client to dispute or delay payment. Include dates, deliverables, and any agreed reference numbers.

Setting payment terms

Payment terms tell your client when you expect to be paid. Common options in the UK:

• Due on receipt — payment expected immediately
• Net 7 — within 7 days
• Net 14 — within 14 days
• Net 30 — within 30 days (the most common)

If you don't specify payment terms, the default under UK law is 30 days from the date the invoice is received. But "default" doesn't mean "best" — for smaller projects, Net 14 or even due on receipt gets your money faster.

State your terms clearly on the invoice. Don't bury them in small print.

Common invoicing mistakes

1. Not sending the invoice promptly. Send your invoice as soon as the work is delivered. Every day you delay is a day added to your payment timeline.

2. Missing or wrong details. A wrong address, missing invoice number, or incorrect amount gives your client a reason to "query" the invoice — which means weeks of back-and-forth before you get paid.

3. No payment link. If your client has to look up your bank details, find a chequebook, or phone their bank, you've added friction. Include a direct payment link on every invoice. Coinvoice invoices include a one-click "Pay Now" button that accepts card and PayPal.

4. Not following up on overdue invoices. If your invoice is overdue, send a polite reminder. Under the Late Payment of Commercial Debts Act, you're entitled to charge interest on late payments — read our guide to dealing with late payments for details.

5. Inconsistent formatting. Using a different layout every time looks unprofessional and makes record-keeping harder. Use a consistent invoice template or invoicing tool.

Do I need to charge VAT?

Only if you're VAT-registered. You must register for VAT if your taxable turnover exceeds £90,000 in any 12-month period (as of 2026). You can also register voluntarily below this threshold.

If you're not VAT-registered, do not show VAT on your invoices. You can include a line saying "Not VAT registered" if you want to be explicit.

If you are VAT-registered, your invoice becomes a "VAT invoice" and has additional requirements — see our VAT invoice guide.

How long should I keep invoices?

HMRC requires you to keep records for at least 5 years after the 31 January submission deadline of the relevant tax year. For VAT-registered businesses, keep records for 6 years.

This includes both invoices you've sent and invoices you've received (for expenses). Digital records are fine — you don't need paper copies.

Creating your first invoice

The fastest way to create a professional invoice is with a dedicated tool. You can use our free invoice generator to build and download a PDF right now, no account required.

If you want to send invoices by email, track payments, and get paid online, sign up for Coinvoice — it's free for up to 25 clients with unlimited invoices.