Guides · Updated 10 October 2026

How often should you re-check a customer’s VAT number?

VAT numbers stop being valid without anyone telling you. When to check again, and what to do when a number you rely on is no longer valid.

Why a number that was valid can stop being valid

A VAT number isn't permanent. Businesses close, merge, fall below their country's registration threshold and deregister, or go into insolvency. Tax authorities also cancel numbers themselves, for example when a business stops filing returns or turns out to be a missing trader in a VAT fraud. Nobody tells the business's customers or suppliers when this happens.

A VIES check only answers one question: is this number valid right now? It can't tell you whether it was valid last month. So a check you made when you took on a customer says nothing about an invoice you send them a year later.

When to check

• When you take on a new customer or supplier, before the first invoice you zero-rate or reverse-charge. How to check properly.
• When their details change: a new name, a new address, a new VAT number, or a request to send invoices somewhere else.
• Before a large or unusual invoice, especially a one-off sale of goods to a business you don't know well.
• Regularly for everyone you invoice without VAT. Many businesses re-check their whole list before each EC Sales List or VAT return, so a cancelled number is caught within one period.

There is no single EU rule that sets how often you must check. What tax authorities look for is that you acted with reasonable care: that you checked, kept a record, and reacted when something changed. See what proof of a check to keep.

What to do when a number is no longer valid

1. Make sure it isn't an outage. "Could not check" is not "invalid". If the country's database is down, try again later; see VIES is down: what it means.
2. Ask the customer. Often there's an innocent explanation: a new number after a merger, a group registration, or a typo in your records.
3. Until it's sorted out, don't treat them as VAT-registered. Without a valid number, the conditions for zero-rating goods or reverse-charging services may not be met, and you may have to charge VAT as you would to a consumer. Ask your tax adviser if you're unsure.
4. Keep a record of the check, the conversation and what you decided.

Checking a whole list automatically

Re-checking dozens or hundreds of numbers by hand every quarter is the sort of job that quietly stops happening. With Validitool's monitoring, you add your customers' VAT numbers to a watchlist and they're re-checked every day. When one stops being valid, or becomes valid again, you get an email, and a signed webhook if you use the API. Each company is also screened against the EU, UN, UK and US OFAC sanctions lists whenever a list is updated.

Re-checks don't use your monthly checks. A watchlist holds up to 25 numbers on Starter, 250 on Growth and 2,500 on Scale. You can add numbers in the dashboard or through the watchlist API.

This guide is general information, not tax or legal advice. Rules and their application differ by country and by transaction; check with an adviser for your situation.

More guides

• How to check an EU VAT number before you invoice
• VIES is down: what it means and what to do
• The reverse charge explained: EU and UK B2B sales
• What proof of a VAT number check should you keep?
• EORI numbers explained: EU, GB and XI
• Northern Ireland XI numbers: VAT and EORI
• Checking Swiss and Norwegian VAT numbers
• Sanctions screening for small businesses
• Fake invoices and changed bank details: how to spot supplier fraud
• Peppol e-invoicing: what it is and how to check a customer