German tax-number converter: state format → 13 digits
Updated: August 2026 · free · eBilanz Fabrik (a tool, not tax advice)
In short: to transmit via ELSTER/ERiC the tax administration needs the 13-digit federal Steuernummer — not the shorter number printed on your assessment notice. This converter derives it from your state tax number and the federal state. It runs entirely in your browser; your tax number never leaves the device.
Why does it need converting?
Each German state issues tax numbers in its own format — 10 or 11 digits, with different separators. Electronic transmission, by contrast, requires one uniform 13-digit format that prefixes the federal tax-office number. Entering the number straight off the notice usually gets the submission rejected on technical grounds — not because the number is wrong, but because it is in the wrong format.
What this converter does not do
It does not check whether the number is yours, whether it is still current, or which tax office is responsible. It converts one format into another. Your tax office's own details govern; the result is non-binding. This is expressly not tax advice.
Frequently asked questions
Where do I find my Steuernummer?
On every assessment notice and on almost every letter from your tax office, usually top right. In “Mein ELSTER” it appears in the profile of the business concerned.
Is the 13-digit Steuernummer the same as the Steuer-Identifikationsnummer?
No. The Steuer-Identifikationsnummer (IdNr.) has 11 digits and belongs to a person for life. The 13-digit number here is the federal format of the business tax number and belongs to a tax case at a tax office.
My number already has 13 digits — what then?
Then there is nothing to convert: the tool returns it unchanged. That is the normal case if you already know the number from an electronic procedure.
Does my tax number leave the browser?
No. The conversion is plain JavaScript on your device — the page sends the number nowhere, including to us.
Need the number for your e-Bilanz?
eBilanz Fabrik turns your finished Bilanz and GuV into the official XBRL e-Bilanz and transmits it to the tax office via ERiC after your approval. The conversion above is built into that flow, so you do not have to do it separately.