How to number your invoices correctly: sequential, unique, consistent

An invoice number looks like a small detail – until a payment cannot be matched, an invoice goes out twice, or the VAT audit starts asking questions. A clean numbering system from day one saves you hours of searching later. Here is what is required in Switzerland and which formats work well.

What the law actually requires

If you are VAT-registered, every invoice needs a unique, sequential number (Art. 26 para. 1 lit. g VAT Act). In practice, this means: the same number must never appear twice for the same recipient, and ideally the numbers should ascend without gaps.

Key points:

• Unique per recipient: the same number must never reach the same client twice. The simplest solution is a globally unique sequence.
• Sequential means ideally gapless: VAT-registered businesses should not skip numbers. Gaps invite questions during an audit.
• Recommended even without VAT liability: below the CHF 100,000 revenue threshold there is no formal requirement, but a clean system still pays off for your own bookkeeping and for customer queries.

Proven formats for freelancers and small businesses

No regulation prescribes what the number must look like. Three formats have proven themselves:

Format	Example	Suited for
Year + sequence	2026-041	Most freelancers and sole proprietorships
Prefix + year + sequence	INV-2026-041	Anyone also numbering quotes (QUO-) and credit notes (CRE-)
Client + year + sequence	ACME-2026-007	Anyone with many recurring jobs for the same client

Our tip: start with 2026-001. The year prefix has a pleasant side effect: the sequence restarts at 001 each January without ever creating duplicates – uniqueness is preserved automatically.

Can the number restart per client?

Yes, as long as each client + number combination stays unique. Client prefixes such as CLIENT-2026-012 achieve this. For most self-employed people this is unnecessary complexity – a global sequence is simpler and entirely sufficient.

The three most common mistakes

1. Assigning numbers twice – easily happens when invoices originate in parallel from Excel, email templates and software. Using a single source (or software that numbers automatically) solves it.
2. Issuing numbers provisionally and deleting them later – a sent invoice should never be physically deleted. For cancellations, issue a credit note with its own number.
3. Numbering only upon payment – the invoice number is created when the invoice is issued, not when it is paid.

Invoice number vs. QR reference: two different things

Do not confuse the invoice number with the QR reference number on the Swiss QR bill. The QR reference (27 characters) travels with the payment through the banking system and enables automatic matching of incoming payments on your account. Embedding the invoice number in the QR reference is common practice – every incoming payment then immediately identifies which invoice was paid. More details in our article on the Swiss QR bill.

Tools that number automatically

Manual number sequences in Excel work fine up to roughly ten invoices per year. Beyond that, a system pays off: our QR invoice generator lets you manage numbering manually and effortlessly. If you invoice weekly, consider proper invoicing software – the comparison of the best invoicing programs shows the options, and rechnungslösungen.ch offers Swiss software comparisons and templates (in German).

Just founded your company? firma-grunden.ch offers a provider comparison for company formation in Switzerland.

Note: this article is not legal or tax advice.