VAT validity check

Question

I have to build in some VAT formulas in a webpage. When a user fills in a VAT number, i have to check if it's in the right validity format.

The control for Belgium is already done, but I can't find validity formulas for the Netherlands, France and Luxembourg...

Anyone suggestions?

I use Visaul Studio .NET 2008, c#. Visual Basic is fine too :)

Answer 1

Have you considered VIES?

Answer 2

The EU exposes a web service for validating VAT (web form, WSDL).

Following CodeProject article includes a C# code showing how to validate VAT number against this service: http://www.codeproject.com/KB/cs/VATchecker.aspx

Formal validation rules are quite complex. Check table describing VAT number structure in VIES FAQ for some of them. Note, that there is not a exhaustive summary. I would better check the validity using the online web service.