What an invoice PDF must contain: the fields tax authorities actually check

The eleven fields present on a compliant invoice in the EU, UK and US, the ones people forget, and how to bake them into a template so they are never missing.

Updated 31 August 2026

An invoice is a tax document before it is a request for money. Auditors do not care how it looks; they care that a fixed set of fields is present and consistent across the sequence.

Fields that are always required

• Seller's legal name, address and tax registration number (VAT number in the EU/UK, EIN or state tax id in the US where applicable)
• Buyer's legal name and address
• A unique, sequential invoice number
• Issue date; supply date if it differs
• A description of each line: quantity, unit price, net amount
• Tax rate and amount per rate (or the reason none applies — reverse charge, exemption)
• Total net, total tax, total gross
• Currency
• Payment terms and due date

The ones people forget

• Sequential numbering without gaps: a deleted invoice must be replaced by a credit note, not renumbered
• Reverse-charge wording on cross-border B2B services in the EU
• The buyer's VAT number on intra-EU supplies — without it the seller must charge VAT

Bake it into the template

The mistake is leaving fields optional in the form. Make the template fail loudly when a required field is empty, and store the invoice number generator on the server, not in the request. With the API, one JSON object per invoice and the numbering lives in your billing code.