UK VAT Number Checker

Check a UK VAT number before you trust it

VAT numbers are easy to take at face value - they appear on invoices, websites and quotes, and most of the time they're genuine. But a wrong or fake VAT number can cause real problems: if you reclaim VAT on a purchase backed by an invalid number, HMRC can refuse the claim, and a supplier quoting a made-up number may not be VAT registered at all.

This free validator checks, in an instant, whether a UK VAT number is correctly structured and passes HMRC's built-in checksum - a quick first line of defence against typos and fakes.

What a valid UK VAT number looks like

A standard UK VAT registration number is nine digits long, usually written with the "GB" prefix - for example, GB 123 4567 89. Some larger organisations have twelve-digit numbers, where the extra three digits identify a branch or division. Crucially, the nine digits aren't random: the last two are a check that's mathematically derived from the first seven, using an algorithm HMRC publishes.

That means an obviously wrong number - a transposed digit, a missing figure - can be caught instantly without contacting anyone. This validator checks both the length and the checksum, and tells you clearly whether the number is well-formed.

How the checksum works

Without getting too deep into the maths, the first seven digits are each multiplied by a descending weight (8, 7, 6, 5, 4, 3, 2), the results are added up, and that total is combined with the final two "check" digits. If the combination divides cleanly by 97 - under either of the two methods HMRC uses - the number passes.

It's the same principle as the check digit on a credit card or an ISBN: a clever bit of arithmetic that makes accidental errors stand out. Our tool runs both the original and the newer "9755" variant of the calculation, so a valid number always passes.

What this tool does - and doesn't - tell you

It's important to be clear about the limits. This validator confirms a number is correctly formed: the right length and a valid checksum. It does not confirm that the number is actually registered to a real, trading business, or that it belongs to the company quoting it. A number can be perfectly valid in structure but not currently active, or registered to someone else entirely.

For that, you need HMRC's free official service, Check a UK VAT number, which looks the number up against the live register and can even give you a proof-of-check reference. The sensible workflow is: use our tool for an instant structural check, then HMRC's for confirmation when it matters.

Why VAT number accuracy matters

If you're VAT registered and reclaiming input VAT, your claim needs to be backed by a valid VAT invoice - and a valid VAT invoice must show the supplier's correct VAT number. If that number turns out to be wrong or fake, HMRC can disallow the reclaim, leaving you out of pocket. For businesses buying from new or unfamiliar suppliers, a quick validation is cheap insurance.

It's also useful when issuing your own invoices - checking your number is entered correctly avoids your customers' reclaims being questioned. If you handle invoices regularly, our VAT Invoice Checker reviews whether an invoice has all the elements HMRC requires.

VAT registration: the bigger picture

A VAT number means a business is registered for VAT, which becomes compulsory once taxable turnover crosses the registration threshold - though many businesses register voluntarily to reclaim input VAT or to look established. If you're approaching the threshold or weighing up voluntary registration, it pays to understand the mechanics.

Our VAT Calculator adds or removes VAT at the standard or reduced rate, the Flat Rate VAT Calculator models the simplified scheme many small businesses use, and the VAT Return Generator helps you prepare the nine boxes of a return. The official rules live on GOV.UK's VAT registration pages.

Spotting VAT fraud and dodgy invoices

Invalid VAT numbers are sometimes a sign of something worse than a typo. Fraudsters occasionally add a fake VAT number to an invoice to look legitimate or to charge "VAT" they never intend to pass to HMRC. If a supplier's number fails the checksum, or fails HMRC's live check, treat it as a red flag and ask questions before paying.

Combine that with the usual due-diligence signals - a real trading address, a working phone number, consistent company details - and you'll avoid most problems. For larger or first-time transactions, validating the VAT number is a small step that can save a lot of hassle later.

The bottom line

A VAT number carries more weight than it looks: it underpins VAT reclaims and signals that a business is properly registered. Checking one takes seconds and can save you a disallowed claim or a brush with a fake supplier. Use the validator above for an instant structural check, confirm against HMRC's live service when the money's significant, and lean on the rest of our VAT tools to handle invoices, returns and registration with confidence.

Validating EU and international VAT numbers

This tool checks UK (GB) VAT numbers, which follow their own nine-digit format and checksum. If you trade with businesses in the EU, you'll come across VAT numbers in dozens of other formats - each country has its own length and structure. For those, the European Commission runs the free VIES service, which validates VAT numbers across EU member states against their live registers.

Since Brexit, UK VAT numbers are no longer part of VIES, which is exactly why HMRC provides its own separate checking service for GB numbers. The takeaway: use this tool and HMRC's checker for UK numbers, and VIES for EU ones, and don't assume a format valid in one system will validate in another.

Building VAT checks into your processes

For a business that takes on new suppliers regularly, it pays to make VAT validation a routine step rather than an afterthought. A simple habit - validate the number when you set up a new supplier, and again on any invoice where you're reclaiming a significant amount of VAT - catches most problems early.

Keep a note of when you checked a number against HMRC's live service; the service can provide a reference number as proof you checked, which is useful evidence of due diligence if HMRC ever queries a reclaim. Good record-keeping here dovetails with the digital records you'll keep for VAT returns and, increasingly, for Making Tax Digital.

From checking numbers to filing returns

Validating a VAT number is usually just one moment in a wider VAT workflow. If you're registered, you'll be charging VAT, reclaiming input VAT, and filing returns - all of which our tools support. Use the VAT Calculator to add or strip VAT, the Flat Rate VAT Calculator if you're on the flat-rate scheme, the VAT Invoice Checker to make sure invoices meet HMRC's requirements, and the VAT Return Generator to prepare the nine boxes of your return.

Together they cover the everyday VAT jobs a small business faces, without the cost of full accounting software.

A note on Making Tax Digital for VAT

Most VAT-registered businesses must already keep digital VAT records and file returns through compatible software under Making Tax Digital for VAT. That's separate from MTD for Income Tax, which is being phased in for sole traders and landlords. If you run a VAT-registered business, it's worth making sure your record-keeping meets the digital requirements - HMRC's guidance on Making Tax Digital for VAT explains what's needed.

Validating supplier VAT numbers is a small but sensible part of keeping those records clean and your reclaims defensible.

The bottom line on VAT number checks

A VAT number is a small detail that quietly underpins a lot of business trust. It tells you a supplier is registered, and it's the linchpin of any VAT you reclaim on what you buy. Checking one costs you nothing and takes seconds, yet it can spare you a disallowed reclaim, a brush with a fraudulent invoice, or the embarrassment of your own number being mistyped on customer invoices.

The sensible routine is to use this validator for an instant structural and checksum check, then confirm against HMRC's live "Check a UK VAT number" service whenever the amount at stake is significant or the supplier is new. Treat a failed check as a prompt for questions, not an accusation - most failures are honest typos - but don't ignore it.

Combine VAT validation with the rest of good supplier due diligence and clean digital records, and you'll keep your VAT affairs tidy and your reclaims defensible. For everything else VAT-related, from charging and reclaiming to preparing your return, the TaxFly VAT toolkit has you covered.

Finally, keep in mind that VAT rules evolve - registration thresholds, the treatment of digital services, and reporting obligations all change from time to time. A number that was valid and active last year may have been deregistered since, which is another reason to rely on HMRC's live checker for confirmation rather than structure alone.

Bookmark both this validator and HMRC's service, build the check into how you onboard suppliers, and you'll have a simple, repeatable safeguard that protects your VAT reclaims for years to come.