A VAT invoice is not just a payment request — it is the document your customer's accountant uses to reclaim input VAT and the document a tax inspector checks first. Missing a mandatory field can invalidate the customer's reclaim and, in an audit, yours. Here is what the law actually requires.
When you must issue a VAT invoice
- For every B2B supply in the EU — within 15 days of the end of the month of supply (many countries are stricter; Germany and Italy are effectively immediate).
- In the UK, for all standard and reduced-rate supplies to another VAT-registered customer within 30 days of the supply.
- For zero-rated and intra-EU supplies — required even at 0%, including reverse-charge supplies.
Mandatory fields (EU VAT Directive 2006/112/EC, Art. 226)
- Date of issue.
- Sequential, unique invoice number based on one or more series.
- Your full name, address and VAT number.
- Customer's full name and address.
- Customer's VAT number for cross-border reverse-charge supplies.
- Distinct invoice numbers for any credit note referencing the original.
- Description and quantity of goods/services.
- Date of supply (if different from the invoice date).
- Taxable amount per rate, unit price, discounts not in the unit price.
- VAT rate applied per line.
- VAT amount payable (except reverse charge and margin schemes).
- If the customer issues the invoice (self-billing) — the invoice must state "Self billing".
- For margin scheme travel agents and second-hand goods — the specific scheme wording.
Extra fields UK HMRC requires
- Your HMRC VAT registration number (GB + 9 digits).
- For reverse charges: the statement "Reverse charge: VAT to be accounted for by the recipient".
- For global accounting schemes, margin scheme and second-hand goods: the specific disclosures.
Worked example — German supplier invoicing a French business
Invoice 2026-0417 — issued 14 March 2026 Supplier: Muster GmbH, Musterstr. 10, 10115 Berlin, DE123456789 Customer: Boutique SARL, 12 Rue Lafayette, 75009 Paris, FR40303265045 Date of supply: 10 March 2026 Consulting services, March 2026 — €5,000.00 Reverse charge — Article 196 of Council Directive 2006/112/EC VAT: €0.00 — VAT to be accounted for by the recipient
The customer's VAT number must have been valid on VIES at the time of supply — a number deregistered the next day is fine, one invalid at supply date is not.
Currency rules
- You may invoice in any currency, but the VAT amount must also be shown in your own reporting currency (converted at the rate valid at the time of supply or as published by your tax authority).
- Keep the exchange rate source in your records — HMRC accepts its own monthly rates, many EU countries accept ECB rates.
Electronic invoices
- E-invoices are valid in every EU country and the UK, provided authenticity, integrity and legibility are guaranteed (digital signature, EDI agreement, or business-controls processes).
- Italy, Poland (KSeF phasing in), France (mandatory B2B e-invoicing from September 2026) and several others require clearing through national platforms — a plain PDF is not enough there.
- Store invoices for at least 6 years (UK: 6 years for VAT records; some countries require 10).
Top 5 field mistakes we see
- Sequential numbering that resets or skips — series per customer or year are fine, random gaps are not.
- Customer VAT number missing on cross-border invoices.
- Rounding: VAT computed per line vs per invoice total, drifting cents away from the authority's rounding.
- No date of supply when it differs from issue date (common with retainers and subscriptions).
- Reverse-charge wording missing or paraphrased so loosely it does not cite the legal basis.
To check the amounts on any invoice, use the VAT calculator for gross/net splits and country rates to confirm the right percentage was applied.