Validating VAT IDs: Why Reverse Charge Without Verification Is Risky

A business customer from France orders €8,000 of goods, sends over their VAT ID, and you invoice net of tax – reverse charge, the standard case in EU B2B trade. Two years later, a tax audit finds that the number was invalid at the time of supply. The consequence: the transaction is treated as taxable, and the 19% VAT – €1,520 here – is paid by you, because recovering it from the customer afterwards rarely works.

VAT ID validation is therefore not a formality; it is the insurance policy behind every zero-rated B2B invoice. This article explains what to check and when – and how to fit the process into daily operations without extra overhead.

When reverse charge actually applies

For intra-Community supplies and many B2B services within the EU, the tax liability shifts to the recipient: you invoice net with the note “Reverse charge – VAT payable by the recipient”, and the customer accounts for the tax in their own country. At its core, three conditions must hold: the customer is a business, they use a valid VAT ID from another member state, and both numbers (yours and theirs) appear on the invoice.

The critical word is valid – at the time of supply, not at some point. Since the EU “Quick Fixes”, a valid customer VAT ID is a substantive condition of the exemption, not a mere administrative nicety.

Syntax, existence, attribution: the three validation levels

Level 1 – Format. Every country has its own pattern: DE plus nine digits, FR plus eleven characters, NL with a “B” in position ten. Typos and transposed digits fail right here. This check takes seconds and catches a surprising share of errors – our free EU VAT Number Validator validates syntax and country formats directly in your browser, so customer data never leaves your device.

Level 2 – Existence. Whether a formally correct number is actually issued and active is answered by the EU Commission’s VIES database or, for German businesses, by the Federal Central Tax Office (BZSt).

Level 3 – Attribution (qualified confirmation). The gold standard: does the number really belong to this company at this address? The BZSt’s qualified confirmation documents exactly that – and is your strongest evidence in a dispute.

Checking is good, documenting is mandatory

A check you cannot prove might as well not exist for an auditor. Clean practice therefore means: archive the date and result of every check (screenshot or confirmation ID), verify new customers before the first invoice with a qualified confirmation, and re-verify existing customers on a schedule – quarterly is common. If the customer’s name or address changes, a fresh qualified confirmation is due.

Trigger	Recommended depth
New customer, first B2B invoice	Syntax + qualified confirmation
Existing customer, recurring supply	Syntax on every invoice, existence quarterly
Unusually large single order	Fresh qualified confirmation
Change of name or address	Fresh qualified confirmation

What to do when a number is invalid

If validation fails, the rule is: do not invoice net. Ask the customer for a correction or a current confirmation from their tax authority; until then, invoice with German VAT. How to separate gross and net amounts cleanly in that case is covered in our guide to calculating VAT correctly; the bigger picture – OSS, distance-selling thresholds, Amazon FBA warehouses – lives in our article on VAT in e-commerce.

Conclusion: a 30-second check against a 19% risk

Reverse charge is convenient – but only as robust as the VAT ID it rests on. The format check with the free EU VAT Number Validator takes seconds; a qualified confirmation takes minutes. Measured against a 19% back-tax risk on every affected sale, it is the cheapest insurance in B2B trade.

If you issue many B2B invoices, validation should not be triggered by hand at all: KudTax pulls your order and invoice data automatically from shops and marketplaces, matches documents to transactions, and hands everything to DATEV ready to book – so the tax logic per customer is documented and traceable from the start.