What is a VAT number?

In practice, in the UK

HMRC issues the VAT number once a registration application is processed, and businesses often need to trade for a period beforehand using their yet-to-be-confirmed number, adjusting invoices retrospectively once it arrives. The number has a fixed format, and quoting it correctly matters beyond bookkeeping tidiness: a business customer checking a supplier’s VAT number is doing basic due diligence, since a VAT-registered customer needs a valid VAT invoice, including the supplier’s number, to recover the VAT it has been charged. Losing track of the number, or quoting it inconsistently across systems, creates exactly the kind of mismatch a customer’s own checks are designed to catch.

In Odoo

Odoo stores the VAT number on the company record and prints it automatically on outgoing invoices and other statutory documents, so it only needs to be entered accurately once. The more common issue is a business that registers for VAT partway through using Odoo, and forgets to add the number before the first VAT invoices go out, leaving a run of documents that need to be reissued or corrected.

Common mistakes

• Trading and invoicing for a period without a confirmed VAT number, then failing to reissue those early invoices correctly.
• Quoting the VAT number inconsistently across letterhead, invoices and the accounting system.
• Leaving the VAT number field blank in the accounting system after registration, so early invoices are missing it entirely.