VAT number on invoices (UK): format, rules and checks

Your VAT number is what turns a plain invoice into a VAT invoice. Your customers need it to reclaim the VAT you charge them, and HMRC uses it to match your sales to your returns. Get it wrong — print it when you're not registered, or leave it off when you are — and either your customer can't reclaim the VAT or you're showing VAT you aren't allowed to charge.

This guide covers the UK VAT number format, when it must and must not appear, what to do while you wait for yours, and how to check a customer's number. The free UK invoice generator adds the VAT number field when you choose VAT registered and removes it when you don't.

The format

A UK VAT registration number is:

Spaces don't matter: "GB123456789" and "GB 123 4567 89" are the same number. HMRC also issues a few special formats for government departments and health authorities, which you're unlikely to need on your own invoices.

A number that looks right isn't necessarily live. Only HMRC's check service confirms that a number is valid and who it belongs to. Invoice Native checks that your number has the right format as you type.

When the VAT number must appear

Once you're VAT registered, every VAT invoice you issue must show your VAT registration number, alongside your name and address (HMRC VAT Notice 700, section 16). If you and your customer are both VAT registered, you must give a VAT invoice, so in practice the number goes on every invoice to a VAT-registered business.

It also goes on:

• credit notes that adjust VAT on an earlier invoice;
• simplified invoices for sales up to £250 including VAT, if you use them.

When it must not appear

If you're not VAT registered, your invoice must not show a VAT number of any kind:

• don't print a number you've applied for but haven't received;
• never use someone else's number, such as a supplier's or a former employer's;
• don't show a VAT line, even at £0.00.

Only a VAT-registered business may issue a VAT invoice, and HMRC can charge a penalty for showing VAT when you aren't registered. See invoicing when you're not VAT registered.

Waiting for your VAT number

Registration can take a while, and you may pass the £90,000 threshold before the number arrives. In the meantime:

1. Don't show VAT or a VAT number on your invoices.
2. Raise your prices to cover the VAT you'll owe on those sales, and tell customers why.
3. When the number arrives, reissue VAT invoices for the sales made since your registration date, so VAT-registered customers can reclaim the VAT.

Your customer's VAT number

You don't have to show your customer's VAT number on a normal UK invoice, but it's worth adding in two cases:

• The construction reverse charge. The customer must be VAT registered for it to apply, so their number on the invoice shows why you haven't charged VAT. See reverse charge invoices.
• Business clients abroad. An overseas customer's VAT number is the best evidence that they're in business, which is why you don't charge UK VAT. See invoicing overseas clients.

Checking a customer's VAT number

HMRC's Check a UK VAT number service on GOV.UK is free:

• enter the number (you can't search by name);
• it tells you whether the number is valid and the name and address it's registered to;
• if you're VAT registered, you can enter your own number too and get proof of when you made the check.

Check before you rely on a customer's number, especially for a large reverse-charge job or a new customer. If the name doesn't match the business you're dealing with, ask before you invoice.

Common mistakes

• Showing a VAT number while you wait for registration.
• Labelling it "Reg No.", which reads like a company number.
• Dropping the GB prefix or a digit, so the customer's software rejects it.
• Relying on an unchecked customer number for the reverse charge.

Checklist

• VAT registered: your GB VAT number on every VAT invoice and credit note
• Labelled clearly as your VAT number
• Not registered: no VAT number and no VAT anywhere
• Customer's VAT number for reverse-charge and overseas business sales
• Customer numbers checked with HMRC