Invoice number
Invoice numbers: rules and examples
“Sequential invoice number” – few requirements cause as much confusion. Does it have to be 1, 2, 3 without gaps? Can it include the year? What about credit notes? Here are the rules, proven formats and the most common misconceptions.
Start right away: in the Invoice Generator, “Next invoice” increments the number automatically – in any format, with year or prefix.
Write an invoice with a numberThe rules in one sentence
Under § 14 (4) UStG every invoice needs a sequential number based on one or more series, assigned only once to identify the invoice. What matters most: each number exactly once.
- Letters are allowed: “INV-2026-042” is as valid as “42”.
- Several series are allowed, e.g. per year, client, branch or business line – as long as each number stays unique.
- No gap-free requirement: a seamless sequence isn’t mandatory, but you should be able to explain gaps in an audit, e.g. with a kept invoice marked “cancelled”.
Proven formats with examples
| Format | Example | Good for |
|---|---|---|
| Year + running number | 2026-001, 2026-002 | Most freelancers – clear and restarts each year |
| Prefix + year + number | INV-2026-0042 | If you also issue quotes (QT-…) or credit notes (CN-…) |
| Year + month + number | 202610-03 | Many invoices per month |
| Customer number + number | C1042-007 | A few regular clients |
| Plain sequence | 1001, 1002 | Small businesses; starting at 1001 looks more established than 1 |
Avoid numbers made only of the date: two invoices on the same day would share a number.
Set your format once – “Next invoice” takes care of the rest.
Automatic numbering in the Invoice Generator
- Enter your first number in your format in the Invoice Generator, e.g.
2026-001. - After saving, click “Next invoice”: the last group of digits goes up (
2026-002), leading zeros stay, and the date jumps to today. - Client and line items remain – handy for monthly recurring invoices.
Your browser remembers the last number. If you write invoices on several devices, use “Save as file” or keep a short list of the numbers you used.
Credit notes, corrections, small businesses
- Mistake in an invoice: don’t reuse the number. Either issue a correction that clearly refers to the original invoice, or a credit note with its own number followed by a new invoice.
- Small invoices up to €250 need no invoice number (§ 33 UStDV).
- Kleinunternehmer are no longer required to number invoices since 2025 (§ 34a UStDV) – still strongly recommended.
- Self-billed invoices issued by your client use a number from the client’s series.
Invoices with automatic numbering
Sequential numbers in your format, mandatory-details check, EPC QR code, PDF and e-invoice. Free, no sign-up.
Frequently asked questions
Do invoice numbers have to be gap-free?
No. They must be unique and sequential, but a seamless sequence isn’t required. You should be able to explain gaps.
Can invoice numbers contain letters?
Yes. Combinations like INV-2026-042 are allowed.
Can I restart at 1 every year?
Yes, if the year is part of the number, e.g. 2026-001 and 2027-001, so every number stays unique.
Can I start with a high invoice number?
Yes. Numbering doesn’t have to start at 1.
Do Kleinunternehmer need invoice numbers?
Since 2025 they are no longer mandatory (§ 34a UStDV), but recommended.
What number does a credit note get?
Its own new number. It refers to the cancelled invoice, followed by a corrected invoice if needed.
Note: This guide reflects German rules as of October 2026 and is not tax advice. For individual cases – cross-border business or borderline small-business situations – ask a tax advisor.
Sources
- § 14 (4) UStG – mandatory details incl. invoice number (German), gesetze-im-internet.de.
- Sequential invoice numbers: obligations and exceptions (German), Haufe.
- § 34a UStDV – invoices of small businesses (German), gesetze-im-internet.de.