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Invoice number generator

Pick a format, set where you are starting, and take the next numbers. Nothing is uploaded and nothing is kept — an account is what keeps a run going.

Format

Your next numbers

  1. INV-0007Next
  2. INV-0008
  3. INV-0009
  4. INV-0010
  5. INV-0011
  6. INV-0012

Nothing here is saved. Close the tab and the run is gone — the one thing a numbering scheme must not do, so keep it in an account once it matters.

What an invoice number is for

It is how one invoice is told from every other one — in your books, in your client’s, and in an audit. That is why the rules are about the run and not the number.

Why it has to be unbroken

§14 UStG in Germany, §11 UStG 1994 in Austria and Article 226 of the EU VAT Directive all ask for a sequence assigned once and never reused. A missing number has to look like a missing number.

Choosing a format

Plain counts and nothing else. A prefix separates runs that must not mix — one per year, per company, per branch. A date in the number makes the year readable without opening the file.

Doing it in a spreadsheet

All three ways disappoint: typing it by hand until you duplicate one, a MAX() formula that only counts what you remembered to log, or a macro that half the installs refuse to run.

Questions people ask

Can I start at 1 every January?

Yes, if the year is in the number — 2026-001. A bare 1 twice is the same number twice.

Can I skip 13?

No. A gap has to be a gap you can explain, not a preference.

Does it have to be numbers?

No — letters are allowed. It has to be unique and it has to run in order.

What if I used a number twice?

Leave both invoices as they are: issue a credit note against the wrong one, then a new invoice with the next free number. Deleting or editing a sent invoice is what an auditor objects to, not the slip itself.

Can I run several sequences at once?

Yes — one per company, per branch or per year, as long as each is unbroken on its own and a prefix tells them apart. Two runs handing out the same numbers is what is not allowed.