Issuing e-invoices: preparing a design practice

Anyone who has to issue e-invoices should have four things settled beforehand: the route to the file, clean master data, a template for fee and interim invoices, and a test run with validation. Usually the route runs through the invoicing software you already have. Whether and from when the obligation applies to you is for your tax adviser to clarify.

Which deadline applies to you

The governing provision is section 27(38) of the German VAT Act (UStG). Two conditions apply at the same time: the supply must have been made in the stated period, and the invoice must be transmitted by the end of the respective deadline. For the second stage, the previous year’s total turnover also counts, calculated on the basis of consideration received (section 19(2) UStG).

On the wording, a PDF invoice sent in January 2027 for a service performed in December 2026 no longer falls under the first stage (section 27(38) no. 1 UStG; Ministry of Finance letter 2024, margin no. 63). The Ministry’s questions and answers name the same periods (question 11). In addition, a transitional rule for invoices sent by electronic data interchange (EDI) runs to the end of 2027 (point 3, margin no. 65). The statute (retrieved 13.11.2026) contains no postponement of these dates. The obligation covers supplies between businesses established in Germany (Ministry of Finance letter 2024, margin nos. 12 and 13). For taxable services connected with land, supplied to non-businesses such as private clients, an other invoice may be issued (margin nos. 19 and 20). How that plays out for a practice with mixed clients, and when a partial service counts as supplied, is a matter for the tax adviser.

Which routes there are

An e-invoice is a structured data set under the standard EN 16931. In practice that means XRechnung (a plain XML file) and ZUGFeRD (a PDF with embedded XML) from version 2.0.1, except the MINIMUM and BASIC-WL profiles (Ministry of Finance 2024, margin nos. 29 and 30). The data set is what counts (margin no. 31). Three routes are common:

The invoicing software outputs XRechnung or ZUGFeRD. Ask the manufacturer about format and version. KoSIT, the German coordination office for IT standards, gives XRechnung 3.0 as valid until at least 31 July 2027 and expects the final version 4.0 in spring 2027; a preliminary version appeared in September 2026. For ZUGFeRD, the FeRD forum names version 2.5.2 of 4 August 2026.

An external platform or service provider produces the data set from your invoice data. That is permitted, but the supplying business remains responsible for the formal requirements (margin no. 37). According to the Federal Chamber of Tax Advisers, a contract or software certification ensures that the requirements are met.

With ZUGFeRD, the PDF image and the XML must be kept identical in content. The tax authorities lay down no checks for this; the FeRD recommends your own checking mechanisms.

You agree format and transmission route with your client (margin no. 36). Where the obligation applies, consent is no longer needed (margin no. 14).

Mandatory details and master data

The mandatory details are set out in section 14(4) UStG and apply to the e-invoice as well. Which detail belongs in which field is shown by the mapping table from KoSIT and FeRD, which the tax authorities recommend (Ministry of Finance 2026, margin nos. 8 and 9). The software fills the fields from your master data. If something is missing there, it is missing from the invoice. Check therefore:

• full name and address of you and your client,
• tax number or VAT identification number,
• the issue date and a consecutive, unique invoice number,
• service description, time of supply, tax rate and tax amount, or the note on a tax exemption,
• reductions agreed in advance, such as prompt-payment discounts,
• for dispatch, the recipient’s email address and, for public bodies, the routing ID (Leitweg-ID) as buyer reference (BT-10).

An AI can go through your client list for missing or contradictory entries and draw up a list of gaps. You complete and confirm. Invoice data does not belong in a consumer chat service; the article Shadow AI: when staff use private chat services explains why.

Fee invoice and interim invoice

For interim payments on fees, section 15 of the German fee scale for architects and engineers (HOAI) refers to section 632a of the Civil Code (BGB). There the services must be evidenced by a statement that allows a quick and reliable assessment. For the e-invoice a second requirement is added: type and extent of the service must be stated in the structured part precisely enough for the tax rate and place of supply to be checked, without describing every detail (Ministry of Finance 2026, margin nos. 11 and 12). Further detail, such as a breakdown of timesheets, may follow as an embedded attachment. A link is not enough (Ministry of Finance 2025, margin no. 35). Whether a particular statement belongs in the data set or may follow as an attachment depends on the individual case.

Interim, advance and down-payment invoices that you issue before your mandatory date need not be e-invoices, even if the service follows later (Ministry of Finance 2026, margin no. 2). From that date they are e-invoices. For down payments, the Federal Chamber of Tax Advisers describes invoice type 380 with a note in field BT-22; type 386 triggers a warning in XRechnung. The same approach suggests itself for interim invoices, but that is an inference and not a statement in the FAQ.

In the final invoice the interim payments must be deducted. Until 30 June 2030 it is not objected to if this is done as a sum in field BT-113 with the details in field BT-22, or if an embedded attachment is referred to (Ministry of Finance 2026, margin nos. 3 and 4). For e-invoices issued up to 31 December 2026, the tax authorities also do not object if they meet the letters of 2024 and 2025 but not the additional requirements of the 2026 letter (Ministry of Finance 2026, application rule).

Test run with validation

Before the deadline, produce test invoices for your typical cases: a partial fee invoice, an interim invoice, a final invoice with interim payments deducted, and an invoice with a prompt-payment discount. Check each file with a validator. KoSIT provides a validator with an XRechnung configuration and a visualisation component. According to KoSIT, rule changes can temporarily lead to error messages.

The Federal Chamber of Tax Advisers explains what validation does. It finds format errors and business-rule errors. Content errors, such as a wrong tax rate or an inadequate service description, it does not find in most cases. So read the visualisation of every test invoice yourself, and keep the validation report. A fixed program does the checking. Whether amounts and description are right, you decide. Finally, send a test invoice to yourself or to a client who is willing to take part, so that the transmission route is tried out too.

Agreeing with the tax adviser and the client

With your tax adviser you settle which deadline applies to you, when a fee counts as a supply made, which tax rate is correct and how invoices under section 13b UStG are to be treated. Who carries out the technical validation belongs on that list as well; the Federal Chamber of Tax Advisers recommends settling it. With your most important clients you agree format, route, reference numbers and the form of attachments. If you want to plan the changeover as a small project with fixed steps, the article Introducing AI in a small office: the first 90 days offers a frame.

What you can do now

1. Ask your tax adviser for last year’s total turnover and note from when the obligation applies to you.
2. Ask the manufacturer of your invoicing software whether it outputs e-invoices, and in which format and version.
3. Go through your client master data and fill in missing entries, for public bodies the routing ID as well.
4. Produce and validate one test invoice each for fee, interim invoice and final invoice.

General information, not legal or tax advice. Your tax adviser clarifies the individual case. Position as of November 2026.