In short: every UK VAT number carries two built-in check digits, so you can validate the maths instantly — try it below. But passing the maths only proves the number is well-formed, not that it's registered. For that, use the official Check a UK VAT number service on GOV.UK, which also shows the name and address HMRC holds. Do both before you reclaim VAT on any invoice from a new supplier.
Instant check: run the HMRC checksum
Paste a number from an invoice — works with or without the GB prefix and spaces:
Maths check only — it runs entirely in your browser (nothing is sent anywhere). Always confirm registration and trading name on the official GOV.UK checker as well. Tip: GB 123 4567 82 is a valid example to try.
What a UK VAT number looks like
One standard shape, four official variants:
| Format | Example | Who uses it |
|---|---|---|
| GB + 9 digits | GB 123 4567 89 | Standard UK businesses |
| GB + 12 digits | GB 123 4567 89 001 | Large groups registering branches or divisions separately |
| GD + 3 digits | GB GD 001 | UK government departments |
| HA + 3 digits | GB HA 599 | NHS health authorities |
| XI + 9 digits | XI 123 4567 89 | Northern Ireland businesses trading goods with the EU (Windsor Framework) |
For EU member states the layouts differ per country (two letters plus 8–12 characters) — the per-country patterns are on the European Commission's VIES pages.
The two-layer check: maths, then the register
- Checksum (instant, offline). Multiply the first seven digits by 8, 7, 6, 5, 4, 3, 2 and add the products. 97 minus the remainder when divided by 97 gives the check digits. Numbers issued from November 2009 use the parallel "9755" series where the check digits come out 55 lower (mod 97). Our tool above runs both variants.
- GOV.UK lookup (the truth). The official service confirms the number exists today and shows the registered name and address. Compare both with what's on your invoice.
- EU suppliers or customers? Use the Commission's VIES checker. GB numbers left VIES at Brexit; Northern Ireland goods traders appear under the XI prefix instead.
Red flags of a fake VAT number
- The digits fail the checksum — a typo or an invented number; either way, query it before paying.
- The number passes the maths but GOV.UK shows a different business name — a stolen number pasted onto fake invoices is the oldest trick in the fraud book.
- A supplier can't produce a number for weeks but keeps charging VAT on invoices.
- Prices too cheap to be true, pressure to pay quickly, and an unfamiliar new supplier — the classic profile of carousel (missing-trader) fraud.
If a number fails: what to do
- Don't reclaim the VAT yet — input reclaims depend on a valid invoice from a genuinely registered supplier.
- Re-check the digits against the invoice (transposition is the most common cause), then re-run both layers above.
- Ask the supplier to confirm their registration in writing and re-issue the invoice once confirmed.
- Keep a record of the checks you ran and when — that paper trail is your due-diligence defence if HMRC ever queries the transaction.
- If answers don't come and VAT was charged, you can report it via HMRC's fraud reporting service.
Why the checks matter beyond one invoice
Under the "knew or should have known" principle (the Kittel doctrine), HMRC can deny input VAT across a whole transaction chain if your deal was connected to VAT fraud and reasonable checks would have uncovered it. A two-minute checksum plus GOV.UK lookup — filed away with the invoice — is the cheapest insurance in VAT.
⚡ Number checks out? Work out the VAT — free UK calculator Add or remove VAT at 20%, 5% or any rate, with copy-ready net, VAT and gross figures.Frequently asked questions
How do I check whether a UK VAT number is valid?
Two layers. First, the structure: strip the GB prefix and you should have nine digits whose final two pass HMRC's modulus-97 checksum — the tool on this page does that instantly. Second, existence: use the official 'Check a UK VAT number' service on GOV.UK, which confirms the number is registered and shows the name and address HMRC holds for it.
What does a UK VAT number look like?
Nine digits, usually written as GB followed by three blocks, like GB 123 4567 89. Variants exist: branch traders get 12-digit numbers, government departments use GD followed by three digits, health authorities use HA, and Northern Ireland businesses trading goods with the EU use the same nine digits under an XI prefix.
GOV.UK shows a different company name from my invoice — what's wrong?
Possibly just a trading name that differs from the registered legal name — ask the supplier to confirm in writing. If they can't or won't, treat it as a fraud red flag: a number stolen from an unrelated business is a classic fake-invoice trick, and HMRC can refuse your input VAT reclaim.
The checksum passes but GOV.UK says 'not registered' — which is right?
Trust GOV.UK. The checksum only proves the digits are mathematically consistent — anyone can generate numbers that pass it. Registration is today's truth, so a valid-looking number with no record on GOV.UK means ask the supplier to explain before you pay or reclaim anything.
How do I check an EU VAT number?
Use the European Commission's free VIES service. Since Brexit, GB numbers no longer appear in VIES; for Northern Ireland businesses trading goods with the EU under the Windsor Framework, look up the XI-prefixed version of the number instead.
Can I reclaim VAT if a supplier's number turns out to be invalid?
Not safely. Input VAT reclaims depend on holding a valid invoice from a genuinely registered supplier — if the number proves invalid, HMRC can refuse the reclaim or claw it back later. Ask for a corrected invoice with a verifiable number; if you have already claimed, correct it promptly.
Is charging VAT without being VAT-registered illegal?
Yes. Only VAT-registered businesses may charge VAT; an invoice showing VAT from an unregistered trader is unlawful and HMRC treats invented VAT numbers as fraud. If you spot one, you can report it through HMRC's tax fraud reporting service.
Is a VAT number the same as a company number or UTR?
No. A VAT registration number (GB plus nine digits) comes from HMRC's VAT office; a company registration number is the eight-character Companies House identifier; a UTR is the ten-digit tax reference used for Self Assessment and Corporation Tax. Three different systems — a VAT invoice needs the VAT one.
Sources and review
This guide was checked against the official validation services — HM Revenue & Customs' Check a UK VAT number and the European Commission's VIES — on 3 August 2026. The checksum described (modulus 97 with the November 2009 "9755" parallel series) is the algorithm HMRC publishes on request and is current at the review date.
This guide is general information, not tax advice — always rely on the official GOV.UK result as the final word on a number's status. See our disclaimer. Spot an error? Tell us and we'll fix it.