How to validate an EU VAT number before invoicing (VIES), and what to keep as proof

Every reverse-charge invoice you send to a business in another EU country rests on one fact: the client’s VAT number was valid. If it was not, the VAT you did not charge can become your VAT to pay. The check takes thirty seconds; the habit of keeping proof takes ten more. Here is both.

Why the check matters

When you supply services to a business in another member state, VAT is usually due where the client is, and the client accounts for it under the reverse charge (the mechanics are in reverse-charge VAT explained). The condition is that your client is a taxable person — and the evidence tax offices expect is a VAT number valid for intra-EU transactions on the invoice date. If an audit finds the number was invalid and you have no proof you checked, the default outcome is that you should have charged VAT, plus interest.

The same applies to intra-EU supplies of goods, where a valid customer VAT number has been a material condition of the exemption since 2020, not just a formality.

How to validate in VIES

1. Go to the European Commission’s VIES page (taxation and customs section of europa.eu — search “VIES VAT number validation”; do not use look-alike commercial sites for the official check).
2. Select the client’s member state and enter the number without spaces or punctuation, and without the country prefix in the number field. Formats differ: Germany has nine digits, the Netherlands twelve characters ending in B and two digits, Ireland mixes letters and digits. A wrong format returns invalid.
3. Optionally enter your own VAT number in the requester field. This is what generates a consultation number — the reference that proves you checked on that date.
4. Read the result: valid, with the name and address where the member state discloses them, or invalid. Save the page as PDF or note the consultation number, date and result in the client record.

What to keep as proof

• The consultation number (only issued if you entered your own VAT number), the date, and the result.
• The client’s registered name and address as returned, matched against the name on your contract or order. A number belonging to a different entity than the one paying you is a red flag.
• A note of any re-check: for regular clients, once a year or when the client changes legal form, country or name; for one-off clients, at the time of the invoice.

Store it with the invoice. If your invoicing tool validates automatically, make sure it also stores the result — some check silently and keep nothing, which does not help you in an audit.

The EX numbers: the new small-business wrinkle

Since 1 January 2025 the EU cross-border SME scheme lets small businesses use the VAT exemption in other member states. Those businesses are identified by their national number with an EX suffix, validated through a separate checker rather than the standard VIES lookup. If a client gives you an EX number, you are dealing with an exempt small business, not a VAT-registered one: it is still a taxable person for the place-of-supply rules, but the invoicing mentions differ. Rare for now, and worth recognising rather than rejecting as “invalid”.

Automate it

For a one-person business the sane approach is to let the tool do it: most EU-focused invoicing tools and the VAT-automation layer covered in automated VAT filing and compliance tools validate numbers against VIES when you add a client, flag changes, and store the proof. The free EU invoice generator on this site formats the reverse-charge invoice correctly once you have confirmed the number; it does not replace the check.

The takeaway

• No valid VAT number, no reverse charge. The check is a condition, not a courtesy.
• Validate on first contact, save the consultation number, re-check periodically.
• Invalid often means “not activated for intra-EU trade” — the client fixes that, not you.
• EX numbers = exempt small businesses under the 2025 SME scheme; different lookup, different mentions.
• Let your invoicing tool do it and store the proof.

Part of the EU admin guide for solopreneurs.