What belongs on every invoice

Invoices rarely come back because they are too high. They come back because a detail is missing that felt like a formality while writing and looks like a problem at the other end: the date of supply, the number, the breakdown by tax rate. The amount is right, the invoice is not.

So what belongs on an invoice is less a list than a logic. It is the same in almost every market, because the same three parties need the same things. The specific mandatory details and the thresholds underneath are national — this article names the German ones as an example and marks them as such.

Before ticking off a list, look at its purpose. An invoice has to answer seven questions well enough for a third party to understand without further papers — years later, with no way to ask you.

1. Who is issuing it? Fully identifiable, not just a brand name.
2. To whom? So it is clear who paid and who derives rights from it.
3. When was it written? The issue date places it in your books.
4. What was supplied or done? By nature and quantity, not as “repair as per job sheet”.
5. When was it supplied? The second date, often overlooked — it decides the period.
6. How much, and what tax? Separately, where more than one rate occurs.
7. What number does it carry? So the transaction stays uniquely nameable.

You can put those seven questions to an invoice in any market. Where one goes unanswered, the invoice is open to challenge, whatever the local law calls that detail.

The date of supply is the detail most often missing, because it looks as if it coincides with the issue date. Work finished on the 29th and invoiced on the 2nd of the following month falls in two different months — and the date of supply decides the return period.

Three or four checks catch most returned invoices, and take under a minute once they are habit.

One misunderstanding persists about the number: what is usually required is a number issued once only, not an unbroken run. Separate series per location, per year or per line of business are fine, as are digits mixed with letters. What does not work: issuing the same number twice, or altering one afterwards. A credit note gets its own number referring back to the original.

If you would rather not keep these checks in your head, have them shown to you as you write: our fill-in invoice template works out net, tax and gross and flags which mandatory detail is still missing. It runs in the browser and stores nothing.

In Germany the mandatory details are in section 14(4) of the VAT Act. It lists ten points, the last two concerning special cases only: the note about the recipient's retention duty, and the word “self-billing” where the recipient invoices. The other eight cover the seven questions from section 1, plus the issuer's tax number or VAT identification number — either will do.

For small amounts a shorter list applies. A simplified invoice under section 33 of the VAT Implementing Ordinance is permitted where the total does not exceed 250 euros. It needs four things: the supplier's name and address, the issue date, the quantity and nature of the supply, and the consideration and tax amount as one sum with the tax rate or a reference to the exemption. Not required: the recipient's name, an invoice number, and the separate statement of net and tax.

Two traps hide in that. The threshold is a total, that is gross — at 19 per cent that is roughly 210 euros net. And the relief falls away in cross-border cases and wherever the tax liability shifts to the recipient.

Anyone using the German small-business scheme under section 19 of the VAT Act invoices under a provision of its own, section 34a of the VAT Implementing Ordinance: instead of a tax rate and tax amount it shows the total with an express note that the small-business exemption applies. The scheme is available where total turnover in the preceding calendar year did not exceed 25,000 euros and does not exceed 100,000 euros in the current year. Anyone in that position who shows VAT by mistake owes it — the most expensive typing error in this section.

The effect of an incomplete invoice is unevenly distributed, which explains almost every return. For you as the issuer it is effort: correct it, send it again. For a business recipient it can be a tax loss.

The reason transfers, because every VAT system knows it: the right to reclaim tax paid as input tax hangs on the document — not on the payment and not on the contract. In Germany that is expressly in section 15(1) sentence 1 no. 1 of the VAT Act, which requires the business to “hold an invoice issued in accordance with sections 14, 14a”. If a mandatory detail is missing, so is that precondition.

Which is why larger customers check incoming invoices by machine and send them back without discussion. That is not obstruction, it is the only way to secure their own deduction — and why a request for a correction is routine, not a dispute.

The good news: a faulty invoice can be repaired. A correction that unambiguously identifies the original and supplies the missing detail cures the defect. What does not work is a quiet second invoice for the same transaction: two documents for one supply is the worse state to be in.

A second question has joined the question of what an invoice says: in what form it has to arrive. The transferable version: can your business receive an invoice as a structured data set and make it readable — and what format does your market expect? Almost every EU market now has a regime of its own, with its own deadlines and sometimes its own formats, while other countries have no business-to-business mandate at all. A PDF by email counts as an electronic invoice under none of them.

Germany as a named example, and the paragraph here with the shortest half-life: since 1 January 2025 the e-invoice has been the standard case for turnover between domestic businesses. In practice that first means an obligation to receive — the transitional rules in section 27(38) of the VAT Act concern issuing, not receiving. For issuing, paper or another electronic format stays permissible for now: until the end of 2026 generally, until the end of 2027 for issuers whose previous-year turnover did not exceed 800,000 euros, and likewise for agreed EDI procedures. From 2028 it applies without exception. Those dates are German transitional rules and nothing else — do not carry them elsewhere.

For a small business this is less dramatic than it sounds, once two things are settled: a fixed address where electronic invoices arrive, and a way to read and keep the data set. What is kept is the data set itself, not the printout — see Digitising receipts.

On the outgoing side it is a question of software, and therefore one of the questions to settle before the first demo: where invoices arise in the system anyway, the format arises with them. The invoicing of Werkstattsystem, for instance, produces the sales invoice in a structured format and files it numbered, rather than printing and re-scanning it.