Which AI can create invoices? The honest answer

None of them, at least not as invoicing software

No language model should be writing your outgoing invoices on its own. It can draft the wording, describe the work and drop figures into a template. What it cannot do: issue a sequential number exactly once, store the document so it cannot be altered, keep it for eight years, and from 2027 produce a structured format the other side can read by machine. German law requires all four.

The question is fair, though, because the wording is the easy part. Legal duty attaches to numbering, to the tax shown, and to retention. Invoicing software handles those three as a side effect. A chat window handles none.

This article sorts out what you actually need, where AI genuinely helps, and what a wrong tax statement costs. For the opposite direction, incoming post, see our guide to AI in invoice checking.

Ten details decide whether the invoice counts

An invoice is a form with mandatory fields. Section 14 (4) of the German VAT Act names ten of them. Leave one out and your customer loses their input tax recovery, then calls you about it. Check every model-generated draft against this list:

• Full name and address of you as well as the customer.
• Your tax number or your VAT identification number.
• Date of issue.
• A sequential number you issue exactly once.
• Quantity plus trade description of goods, or scope plus type of service.
• Date of supply, where it differs from the date of issue.
• Net amount broken down by tax rate, plus any discount agreed in advance.
• Tax rate and tax amount, or a note pointing to an exemption.
• A note about the customer's retention duty where section 14b (1) applies.
• The word Gutschrift where the customer issues the document themselves.

The sequential number is the hard part

A language model has no memory for numbers. Section 14 (4) no. 4 requires a sequential number issued once, identifying that invoice. A model in a chat window has no idea which number it handed out yesterday. It guesses a plausible one, and with invoice numbers plausible is the opposite of unique.

Storage works the same way. Section 146 (4) of the Fiscal Code forbids any change leaving the original content unidentifiable, as well as changes whose nature makes it unclear whether they were original or added later. A file in your downloads folder fails that test.

Retention is the third duty. Section 14b (1) sets eight years for a copy of every invoice you issue. A chat history is not an archive.

A wrong tax rate costs you the amount you stated

Tax wrongly stated is tax you owe. Section 14c (1) puts it plainly: state more tax than you owe, and you owe the excess too. Subsection 2 goes further: state tax with no right to, and you owe the stated amount outright.

Small businesses get hit hardest. Under section 19 (1), their turnover is exempt while the previous year stayed at or below 25,000 euros and the current year stays below 100,000. A model that dutifully types 19 percent into the template has created an unauthorised tax statement.

The arithmetic: 24 invoices at 800 euros net with 19 percent add up to 3,648 euros of stated tax that you owe, on turnover you could never charge it on. Correction under section 14c (2) sentences 3 to 5 works only once the risk to tax revenue is gone, meaning the customer never claimed the input tax or has repaid it. That means a letter to every customer and an application to the tax office.

From 2027 a PDF no longer does the job

A well-typeset PDF is not an e-invoice. Section 14 (1) defines an electronic invoice as one issued in a structured electronic format enabling electronic processing, matching the European norm under directive 2014/55/EU. Everything else, PDFs included, counts merely as another kind of invoice.

German companies have had to accept e-invoices since 1 January 2025, with no exceptions; an email inbox is enough. Issuing them has transition periods: until the end of 2026 for everyone, until the end of 2027 at or below 800,000 euros of prior-year turnover. From 1 January 2028 it is mandatory in domestic business-to-business trade.

The finance ministry names XRechnung as well as ZUGFeRD from version 2.0.1, excluding the MINIMUM and BASIC-WL profiles. XRechnung stands at version 3.0, in force since 1 February 2024 and valid at least until 31 July 2027. Below 250 euros gross the short form survives, and may still travel as an ordinary invoice.

Three places where AI earns its keep

AI belongs in front of the invoice, never inside it. Your software supplies the mandatory fields; the model supplies the language. Three jobs are worth handing over:

• Describing the work: turning timesheets or scribbled notes into a proper trade description as section 14 (4) no. 5 requires. This is the field audits query most often, because entries like consulting or sundries describe nothing at all.
• Translation: the same description for overseas customers, with your own terminology supplied as a glossary.
• A check before sending: the model reads your draft against the ten mandatory details and reports what is missing. It writes nothing, it ticks boxes.

A prompt that checks instead of inventing

Let the model audit, not fill in. This prompt is the part worth keeping: it produces no figures, it hunts for gaps. Copy it, paste your draft underneath as plain text, and change none of the amounts your software calculated.

"You are an auditor, never an author. Check the invoice draft below against the ten mandatory details in section 14 (4) of the German VAT Act. Return a table with three columns: required detail, found yes or no, quoted text from the draft. Invent nothing and add nothing. Then list, in five lines at most: missing details, vague descriptions of work, and any figure that does not follow from the other figures. Recompute net plus tax against gross and state the result. If the gross amount is 250 euros or less, check only the four details required for small invoices."

On handling customer data inside a prompt, see our article on redacting before an AI prompt; the free tool sits at prompt redaction.

Recommendation: 119 euros a year against 3,648 euros of exposure

Buy invoicing software, even for twelve invoices a year. sevdesk lists its Rechnung tier at 11.90 euros gross per month billed monthly, or 9.90 billed annually, so 142.80 or 118.80 euros a year; its free tier allows three invoices a month and outputs ZUGFeRD as well as XRechnung. Against the 3,648 euros above, that is roughly one thirtieth.

I would say no to a pure AI setup in every case where tax is stated or business customers are billed. I would say yes to AI, today, for describing the work, translating it, and checking the draft before it goes out. Those are the places where language really is the problem.

To get the stage before invoicing right, see our guide to writing quotes with AI. For rebuilding the whole document path, our process automation services lay out the approach.

Questions that keep coming up

Three questions recur. The answers sit in the statute, not in product descriptions.

• May ChatGPT write an invoice? The wording yes, the document no. Numbering, immutability and archiving all live outside the chat window, and without them the text is not a valid record.
• Is a Word template enough? For small invoices up to 250 euros gross, yes, provided you keep the numbers in a register and store the files so they cannot be altered. In domestic business-to-business trade that ends with the e-invoicing duty.
• Can AI produce an XRechnung file? Technically yes, it is XML. That does not help: validity is decided by a validator against the published rules, and your invoicing software ships one.

What to do this week

Take your most recent outgoing invoice and walk the ten points. Ten minutes. If nothing is missing, move on to format: check whether your software outputs XRechnung or ZUGFeRD 2.0.1 or later, and if not, when the vendor plans to.

If something is missing, fix the template first and the workflow second. If you are unsure which of the three duties is shaky in your own house, request an initial consultation.