"Can you quickly change that booking from the 12th?" — In a spreadsheet: no problem. In proper German bookkeeping: exactly what the GoBD rules are designed to prevent. The technical term for this is Festschreibung — finalizing records so they become immutable — and it is the core of what a real monthly close means.

In this article we look at what the GoBD actually require, why "locking" is more than "exporting" — and what a clean monthly close looks like in e-commerce practice.

No erasing: what the GoBD demand

The GoBD ("principles for the proper keeping and retention of books, records and documents in electronic form and for data access", a directive of the German Federal Ministry of Finance, most recently issued November 28, 2019) spell out what the German Fiscal Code has long required. Section 146 (4) AO puts it plainly: a booking or record may not be altered in a way that makes its original content unrecognizable.

From this follows the principle of immutability: once a business transaction has been booked — that is, finalized ("festgeschrieben") — it must not be silently changed or deleted. Mistakes are not erased; they are corrected via reversal or re-booking, so the original state remains traceable.

Timing matters too: bookings should be captured and finalized promptly. In practice, a monthly rhythm has become the standard — by the time a month's advance VAT return is filed, its bookings should be locked. Books that stay "in draft" for months are a classic finding in German tax audits.

Locking means: a month becomes final

A GoBD-style monthly close therefore consists of two inseparable steps:

Export — the month's booking data is written out completely, in an analyzable format (typically a DATEV booking batch for your tax advisor).
Lock — the very same records are permanently frozen in the system: no editing, no deleting, no after-the-fact "optimizing".

The second step is the decisive one — and exactly the one many tools skip. An export without a lock is just a snapshot: whatever you change afterwards silently diverges from what your tax advisor has booked.

That is why in KudTax both steps are a single action: on the Exports page you pick the month, check the preview (a true dry run that changes and locks nothing) — and then confirm "Export & lock". A confirmation dialog leaves no room for doubt about what happens: all invoices and transactions of that month are exported and permanently locked. The action cannot be undone — there is deliberately no "unlock" feature.

One month, one booking batch

The export format is no home-grown invention but the standard every German tax firm works with: a DATEV booking batch (Buchungsstapel) in the EXTF format (format version 700/13, the canonical 126-column layout).

The special part: KudTax produces one combined batch for the month, bringing together both sides of an e-commerce business —

the invoice leg: revenues and fees from your sales invoices, with document reference, tax key and accounts from your account configuration,
the bank leg: the matched payouts from marketplaces and payment providers.

Both land in a single batch; the month is closed as one unit — instead of separate exports nobody can ever piece back together. The generated batch also carries the Festschreibung flag, so on the DATEV side the bookings are finalized on import rather than arriving as loose drafts.

You download the file and hand it to your tax advisor or import it into DATEV — automatic online transmission is deliberately not part of the process.

What happens to locked records

After the close, KudTax enforces immutability in the system itself — not just as a warning label:

Locked invoices and transactions can no longer be edited or deleted. The server blocks every modification attempt, including line-item changes and bulk actions.
Matching and unmatching payments is blocked for locked records too — the reconciliation of a closed month stays exactly as it was exported.
In the tables, locked rows are marked with a lock badge explaining that the record has been exported and can no longer be changed.
Future exports exclude locked records by default — so a month cannot accidentally end up in a batch twice.

And if an error does surface after the close? Then the GoBD principle applies: the old record stays put, and the correction is made as a new, offsetting entry in the following month — exactly how your tax advisor would handle it.

The export history: every close stays retrievable

Part of a proper close is that it is reproducible. Every committed export therefore lands in the export history — with type, format, period, row count and file size. The generated file is stored and can be re-downloaded at any time: the exact file that went to your tax firm back then.

That pays off at the latest when questions come up — from your tax advisor ("can you send me March again?") or in a tax audit, when you need to prove what was locked, and when.

For everything else there is the free download next to it: export any day range as a file, as often as you like — this path never locks anything and changes nothing. The line between a casual data pull and a real close stays crisp.

Conclusion: Festschreibung is a feature, not an obstacle

At first glance the GoBD lock looks like a restriction — in reality it is what makes your books trustworthy: a closed month is final, traceable and reproducible at any time.

A clean monthly close needs three things: a complete export (ideally as a combined DATEV booking batch), a hard lock on the exported records in the system, and a history from which every close can be downloaded again. That is precisely how the monthly close in KudTax is built — preview, one deliberate click on "Export & lock", and the month is closed.

For how to handle inbound and outbound invoices in structured formats, read our article on e-invoicing in 2026.

GoBD Festschreibung: what the monthly close really means