Consecutive Invoice Numbering in Switzerland: The Rules That Matter

Swiss bookkeeping expects every invoice to carry a unique, consecutive number. It is not just tidy — it is one of the core requirements for proper accounting and a clean VAT audit trail.

Why consecutive numbers matter

The Federal Tax Administration and your cantonal tax office use invoice numbers to verify that no invoices have been hidden or duplicated. A gap in the sequence can trigger questions during an audit, even when it is completely innocent.

The obligation comes from the duty of proper bookkeeping under the Code of Obligations (Art. 957a OR). In practice, auditors read your numbering as evidence that your books are complete and that no turnover has slipped out of the record.

A clean, unbroken sequence is also a practical tool. When a client disputes a payment or claims they never received an invoice, you can point to the number and the date it was issued and settle the question in seconds.

For VAT-registered businesses the number matters twice over. Your invoice must be clearly identifiable as required by the VAT ordinance (MWSTV), and the number is the simplest way to prove that each taxable turnover appears exactly once in your reporting.

The rules of a clean sequence

Every invoice you issue must carry a number, and that number must be unique. You may never assign the same number to two different documents, because that would make both of them impossible to trace reliably.

The numbers should follow one another without arbitrary jumps. Starting at 1 and counting upward is the safest approach; it leaves nothing to explain if the tax office ever asks to see your full list of issued invoices.

Consecutive does not mean you may never have a gap at all. An occasional missing number that you can explain is normal, while a sequence that leaps around randomly looks like you are hiding something.

Decide on a single scheme and stick to it. Mixing yearly series, project codes and plain counters in the same book makes reconciliation harder and gives an auditor more to question, not less.

Handling gaps and cancelled invoices

If you skip a number by accident, leave the gap alone. Do not go back and reuse the number on a later invoice, because that breaks the one-to-one link between a number and a document.

A cancelled invoice still keeps its number. Mark it as cancelled in your system and move on; the number is used, and the cancellation note explains why it never produced a payment.

Never delete an invoice that has already been issued. Deleting removes the number from the sequence and leaves a hole that looks far worse than a cancelled invoice with a short note.

Keep a running log if you use paper or a spreadsheet. A simple table of number, date, client and amount lets you see at a glance whether your sequence is complete and where any gap appeared.

Restarting a new series each year

Many Swiss businesses restart their numbering on 1 January with a year prefix, such as 2026-001, 2026-002 and so on. This is completely acceptable and widely used.

The prefix is what keeps the sequence unique across years. Without it, two invoices numbered simply 001 in different years would collide, and the whole point of the numbering is lost.

If you restart annually, state the scheme in your bookkeeping so an auditor understands it. A short note such as "numbering restarts each calendar year with a year prefix" removes any ambiguity.

Do not restart mid-year and do not mix schemes. Pick a start date — the first of the year is simplest — and apply it consistently so every number remains traceable to a single invoice.

• Use a year prefix such as 2026-001.
• Never reuse a number, even for a cancelled invoice.
• Leave accidental gaps as they are — do not backfill.
• Document your scheme so an auditor can follow it.