An invoice needs a unique sequential number, the date it was issued, the identity and address of both parties, a description of what was supplied with quantities and prices, the tax applied, and the total due. In the European Union that list is set by law for VAT-registered businesses; in the United States there is no federal requirement at all, and the contents are whatever your client’s accounts payable system asks for.
That asymmetry is why an invoice that has been accepted for years at home can be rejected on a first cross-border job. Neither document is wrong — they were written against different rulebooks.
What does an EU VAT invoice have to carry?
The VAT Directive sets a common list that member states implement, so the particulars are broadly the same across the bloc even though the wording and the rates are local.
| Required particular | Why it is there |
|---|---|
| Date of issue | Fixes the accounting period |
| Sequential number | Proves no invoice is missing |
| Supplier VAT identification number | Identifies who owes the VAT |
| Customer VAT number, where required | Needed for reverse charge and cross-border supplies |
| Full name and address of both parties | Identifies the transaction |
| Quantity and nature of the supply | Describes what was sold |
| Date of supply, if different from issue | Fixes when VAT became due |
| Taxable amount per rate | Separates rates on a mixed invoice |
| VAT rate and amount payable | The tax itself |
| Specific wording where a scheme applies | Reverse charge, margin scheme, exemption |
Simplified invoices are permitted below a threshold that varies by member state, with a shorter list. The full list applies to anything cross-border.
What does the United States require?
Nothing, federally. There is no VAT, no national invoice format and no statutory particular. What exists instead is a set of practical requirements imposed by the buyer: a purchase order number, a vendor identifier, remittance details, and a description that matches what was authorised.
Sales tax, where it applies, is a state matter and is charged on goods and on some services by the seller in states where they have a tax obligation. It appears on the invoice as a line and is not the same object as VAT — it is collected once, at the final sale, rather than at each step.
The consequence for a freelancer invoicing across the Atlantic is that the American client will usually accept a European-style invoice without comment, while the European client may reject an American-style one for missing a VAT number.
What does the number actually have to do?
Be unique and sequential, with no gaps that cannot be explained. The sequence is what lets an auditor establish that no invoice has been quietly removed, which is the entire point of the requirement.
- A gap needs a reason. A cancelled invoice stays in the sequence, marked as cancelled, rather than being deleted.
- Prefixes are fine. Per-year or per-client prefixes are permitted as long as each series is itself sequential.
- Restarting annually is normal. 2026-001 following 2025-214 is a clean sequence, not a gap.
- Never reuse a number. A corrected invoice gets a new number and references the old one, usually as a credit note.
What about reverse charge?
It moves the obligation to account for the VAT from the supplier to the customer, and it applies to most business-to-business supplies of services across EU borders. The supplier charges no VAT and states on the invoice that the reverse charge applies.
Two things have to be right for it to work: the customer’s VAT number must be valid and shown on the invoice, and the wording must be present. An invoice missing either can leave the supplier liable for VAT that was never charged.
What makes an invoice get paid faster?
Precision about the three things a payables clerk needs to match it against something.
- The purchase order or reference the client gave you, quoted exactly.
- A description that matches what was approved rather than what you would call it.
- Payment terms and a due date stated as a date, not as "30 days".
The most common cause of a late payment is not reluctance, it is a mismatch that puts the invoice into a queue for someone to resolve. Everything above is a way of staying out of that queue.
Questions people ask
Does an invoice need a signature? Not generally, in either system. It is a demand for payment rather than a contract, and the underlying agreement is what is signed.
Is a PDF acceptable? Almost universally. Some jurisdictions have moved to structured electronic invoicing for public-sector suppliers, which is a specific format rather than a document, and those rules are being extended in several countries.
How long do invoices have to be kept? Longer than most people expect — commonly six to ten years, set locally and applying to both issued and received invoices.
What if the client is not VAT-registered? Then a cross-border supply is usually treated as business-to-consumer, VAT is charged at the supplier’s or the customer’s local rate depending on the supply, and reverse charge does not apply.
Build the document against the rules of the buyer’s jurisdiction rather than your own. The invoice generator leaves the address blocks long enough for whatever your jurisdiction expects, the percentage calculator handles the tax lines, and PNG to PDF is there for the receipts that have to travel with it.