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When to Validate a Customer's VAT Number
Most people asking "when should I validate a customer's VAT number?" already know how to check one — paste it into VIES, get a yes or no. The harder question is timing: at what points in the customer relationship does the check actually matter, and what happens to the answer between those points. A VAT number you validated at signup can be cancelled the following week, and the check you ran then says nothing about the invoice you issue six months later.
This guide walks through the moments that trigger a validation, why each one matters, and what to keep afterwards. The scope is the EU-27 plus XI (Northern Ireland) — the area VIES covers. It is general information about EU VAT, not tax advice.
Why timing matters more than the check itself
