USt-IdNr. Checker (Germany)

What this does and does not tell you

This page checks arithmetic, not registration. Every USt-IdNr. carries a check digit calculated from the digits before it, which is what catches a typo. Confirming that a business is genuinely registered means asking Bundeszentralamt für Steuern, because only they hold the register.

Questions people ask

Does a valid check digit mean the business is registered?

No. It means the number is well formed. A number can pass the check digit and belong to nobody, or belong to a business that has since deregistered. Only Bundeszentralamt für Steuern can confirm a live registration.

Why does my supplier's number fail?

Nearly always a typing error: a digit read wrong off a printed invoice, or two digits swapped. Check digits are designed to catch exactly these. Read the number back from the original document before you tell the supplier anything is wrong.

Is my number sent to a server?

No. The check runs in your browser. Nothing you type here leaves your device, and nothing is logged.

What is a check digit?

The last character of the number is computed from the others by a fixed rule. If you change any single character, the rule stops matching. That is how a tax authority catches a mistyped number without looking it up.

Can I check numbers from other countries here?

Only the editions that have a published algorithm. Each country uses its own rule, so a number valid in one place will fail everywhere else. Use the edition that matches the number.

Do I need a valid USt-IdNr. to invoice?

If you charge VAT (USt), your own number belongs on the invoice, and in most cases your customer's does too on a business sale. Getting either wrong can hold up their claim, which is the practical reason to check before you send.