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Invoice Numbers in Switzerland: Everything on Requirements, Format and Numbering

Every invoice you issue in Switzerland needs an invoice number. This is not optional — it is a legal requirement under Art. 26 VAT Ordinance (MWSTV) and OR Art. 469. The invoice number must be unique, sequential and gap-free. Which format you choose is up to you. The FTA (ESTV, the Swiss Federal Tax Administration) does not prescribe a specific form, but requires that each number appears only once and that the sequence is traceable. In this guide, I show which formats work well in practice, what to do when errors occur, and how the right software can save you from numbering altogether.

The Most Important Points at a Glance

• Every invoice needs a unique, sequential invoice number — legally required under Art. 26 MWSTV. No exceptions.
• No legally prescribed format — but the number must be unique and traceable. Common formats: 2026-001, RE-2026-001 or simply 1, 2, 3.
• Gaps in your numbering can raise questions during an FTA audit — in the worst case, the FTA estimates your revenue higher and you pay additional VAT of CHF 1,000.00 to CHF 5,000.00.
• Duplicate invoice numbers are a common mistake — easy to make with manual assignment, especially when you issue several invoices per day.
• Software like Magic Heidi generates the invoice number automatically and error-free — from CHF 25.00 per month, significantly cheaper than bexio at CHF 52.00.

What Is an Invoice Number and Why Does Every Invoice Need One

The invoice number is a unique identifier for each individual invoice. It serves identification purposes — for you as the invoicer, for your customers, and for the FTA. Without an invoice number, an invoice cannot be clearly assigned or placed in a gap-free sequence.

The legal basis for the invoice number in Switzerland lies in two laws. Art. 26 of the Value Added Tax Ordinance (MWSTV) requires that an invoice contains certain mandatory details — including a unique invoice number. OR Art. 469 (the Code of Obligations) regulates the general contents of an invoice and requires proper identification. Together, both provisions create a clear rule: no invoice without a number. The full legal texts are available on admin.ch under the Systematic Collection of Laws.

The FTA uses the invoice number to verify during a VAT audit that all revenue has been recorded. The logic is simple: if your invoice numbers are sequential (1, 2, 3, 4, 5 …), the FTA can match the highest number with the count of submitted invoices. If numbers are missing or there are gaps, the FTA asks — and if you cannot provide a plausible explanation, it can estimate your revenue. That can get expensive, as we will see later in Marco's example.

For your own bookkeeping, the invoice number is just as important. You need it to match payments, reference reminders, and find the right invoice when customers enquire. Anyone who has ever tried to match a payment of CHF 2,350.00 without a unique invoice number knows why the number exists.

Mini-Story: Thomas, Photographer from Bern

Thomas is a freelance photographer in Bern. He issues about 60 invoices per year and numbers them manually in the format 2026-001, 2026-002 and so on. In March 2026, things are rushed: two customers want their invoice on the same day. Thomas quickly types 2026-047 — and forgets that he already used this number a week earlier for another customer. Both invoices carry the number 2026-047.

During a routine VAT audit six months later, the FTA auditor notices that invoice number 2026-047 appears twice. He asks Thomas for the original invoice. Thomas can produce both invoices but has to cancel both and reissue them with new numbers (2026-047 and 2026-048). The correction effort costs him half a day — time he could have better spent on client work.

Thomas's takeaway: "I always thought that would never happen to me. But with 60 invoices a year, a single moment of distraction is enough to assign a duplicate number."

Assigning Invoice Numbers: How the Most Common Formats Work

Swiss law does not prescribe a specific format for invoice numbers. You can design them yourself — as long as each number is unique and the sequence is traceable. In practice, several formats have become established, each suited to different business types and personal preferences.

Format 1: Year Prefix with Sequential Number

The format YYYY-NNN (e.g. 2026-001, 2026-002, 2026-003) is the most common variant among Swiss freelancers. The advantage: you can tell at a glance which year the invoice is from. This is especially practical when you have customers who reference an old invoice the following year. The sequential number restarts at 001 each year.

Example: Sandra, a freelance graphic designer from Zurich, uses the format RE-YYYY-001. With 150 invoices per year, she keeps perfect track. Invoices RE-2026-001 through RE-2026-150 are neatly documented. When a customer calls and asks about "invoice RE-2026-047," Sandra knows immediately: an invoice from 2026, the 47th in the series.

The best part: Sandra's VAT filing with the FTA now takes 15 minutes instead of the two hours she used to spend with unsorted invoices. The format saves not only time on filing but also on customer enquiries and payment matching.

Format 2: Prefix with Sequential Number Without Year

A simple RE-001, RE-002, RE-003 also works, especially if you do not issue many invoices per year. The downside: with many invoices, the number gets large (RE-0457), and you can no longer tell at a glance which year the invoice is from.

Example: A freelancer who issues 20 invoices per year reaches invoice number RE-100 after five years. That is manageable, but during an FTA audit the auditor has to reconstruct the years based on the invoice date, not the number.

Format 3: Customer ID Plus Number

If you have many recurring customers, you can use a format like CUSTOMER-001 — e.g. MEYER-001, MEYER-002, MEYER-003. The advantage: all invoices from one customer are immediately recognisable. The downside: the number is not globally sequential, which makes things more complicated during an FTA audit. You then need to maintain a separate, sequential list of all invoices.

Tip: If you want to use this format, make sure to keep an additional master list of all invoices in a spreadsheet or software. Without this list, you will quickly lose track.

Format 4: Date-Based

A format like 20260715-01 (date + daily counter) is rare but possible. It suits businesses with very many invoices per day. For freelancers, it is less suitable since the number is long and hard to remember.

Which Format Is Best?

For most Swiss freelancers and small businesses, I recommend Format 1 (YYYY-NNN or RE-YYYY-NNN). It is simple, readable, and meets all FTA requirements. Anyone who wants to write an invoice that looks professional and is legally sound has a safe choice with this format.

Sequential Numbering: What the FTA Really Requires

The FTA refers to "sequential numbering" in its practical guidance. What does that mean specifically? And what happens if your numbering is not perfectly sequential?

The core requirement of the FTA: every invoice must have a unique number. No number may appear twice. The number must be sequential — meaning the numbers should follow a logical, traceable order.

What the FTA does not require is strict mathematical gap-free numbering. If you assign the number 2026-003 and then realise you forgot 2026-002, you do not necessarily have to leave a gap. You can assign 2026-002 retroactively if the invoice has not yet been sent. What matters is that you document every assigned number cleanly.

What Happens During an FTA Audit

During a VAT audit, the FTA typically requests all invoices from a certain period. The auditor matches the invoice numbers with the submitted VAT returns. If gaps appear, they ask. Typical questions:

• "Invoice number 2026-012 is missing from your list. What happened to this invoice?"
• "You cancelled invoice 2026-045 but did not issue a credit note with its own number. Can you explain?"
• "The invoice numbers jump from 2026-050 to 2026-053. Were numbers 051 and 052 cancelled?"

If you have clear answers to these questions — "Invoice 012 was cancelled because the customer cancelled the order," "Credit note issued as number 2026-046" — everything is fine. The FTA accepts gaps as long as they can be explained.

Mini-Story: Marco, Carpenter from Lugano

Marco is a carpenter in Lugano and runs a sole proprietorship (Einzelfirma). He issues about 40 invoices per year. In the first six months of 2026, he forgets to keep track of his invoice numbers. He numbers the first invoices 1, 2, 3, then forgets, takes a break, and when he resumes issuing invoices, he starts again from 1.

During the annual VAT audit the following year, the FTA auditor notices that several invoices carry the same number and others have no number at all. Marco cannot prove that all revenue was invoiced. The FTA estimates his revenue higher based on bank transfers and sets the VAT accordingly.

The result: Marco has to pay CHF 3,400.00 in additional VAT — money he had actually earned but now has to pay extra to the FTA. If he had used a simple, sequential numbering system, the audit would have been done in 30 minutes. The detailed information from the FTA (ESTV) on invoicing is worthwhile for anyone who wants to avoid similar mistakes.

Tips for Clean Sequential Numbering

1. Use a consistent format and stick with it. Do not change the format mid-year.
2. Keep a simple list of all assigned invoice numbers — ideally in software that handles numbering automatically.
3. Document every break in the numbering: cancelled invoices, credit notes, accidentally skipped numbers.
4. Check your VAT return for gaps in invoice numbers before submitting — this gives you time to clarify any uncertainties before the FTA asks.

Invoice Numbers for Credit Notes and Corrections: What to Do About Errors

Mistakes happen. An invoice is issued incorrectly, a customer cancels an order, an amount is wrong. What happens to the invoice number in these cases?

Credit Note (Stornorechnung)

When you cancel an invoice, you must issue a credit note (Stornorechnung). This credit note needs its own, new invoice number from the sequential series. It references the original invoice (e.g. "Credit note for invoice 2026-047") but has its own number — for example 2026-048.

The original invoice number is retained. It is not deleted or overwritten. In your bookkeeping, you note that invoice 2026-047 was cancelled by credit note 2026-048.

Example: You issued invoice 2026-047 for CHF 1,500.00. The customer complains that an item is incorrect. You issue a credit note 2026-048 for CHF -1,500.00 and then a new invoice 2026-049 for the corrected amount of CHF 1,350.00. The VAT entry shows: CHF 1,500.00 (invoice 047) minus CHF 1,500.00 (credit note 048) plus CHF 1,350.00 (invoice 049) = CHF 1,350.00 effectively invoiced.

Correction Invoice

A correction invoice corrects an already issued invoice without completely cancelling it. The correction invoice also needs its own invoice number from the sequential series.

Example: You issued invoice 2026-050 for CHF 2,000.00 but forgot a discount of CHF 200.00. You issue a correction invoice 2026-051 that adjusts the amount by CHF -200.00. The effective receivable is now CHF 1,800.00.

Advance Invoice and Final Invoice

For larger projects, you often issue an advance invoice and later a final invoice. Each of these invoices needs its own number from the sequential series.

Example: A project worth CHF 10,000.00 is billed in three instalments:

• Advance invoice 1: 2026-060 — CHF 3,000.00
• Advance invoice 2: 2026-075 — CHF 3,000.00
• Final invoice: 2026-089 — CHF 4,000.00

The numbers do not need to follow each other directly, as long as the overall sequence is documented without gaps. Between 060 and 075 are other invoices for other customers — that is perfectly fine.

What to Do About Gaps?

Gaps in invoice numbering are not forbidden, but they must be explainable. Typical legitimate reasons for gaps:

• An invoice was prepared but the order was cancelled before the invoice was sent.
• An invoice number was accidentally skipped.
• An invoice was cancelled without a credit note being issued (only acceptable for small amounts).

Keep a simple log: "Invoice number 2026-052 cancelled, order cancelled, 15 April 2026." That is sufficient as an explanation for the FTA.

Common Mistakes in Invoice Numbering — and How to Avoid Them

In practice at Magic Heidi, we see the same mistakes over and over. Here are the five most common and how to avoid them.

Mistake 1: Duplicate Invoice Numbers

This is the classic. With manual numbering, you forget which number you last assigned and type the same number again. The result: two invoices with the same number, confusion in your bookkeeping, and potentially a query from the FTA.

Solution: Use software that assigns the invoice number automatically. If you number manually, keep a central list (spreadsheet, notebook) and mark each assigned number immediately.

Mistake 2: Gaps Without Explanation

You accidentally skip a number — "2026-047, 2026-049" — and weeks later you cannot remember why. The FTA asks, and you have no answer.

Solution: Document every gap immediately. A brief entry in a spreadsheet is enough: "2026-048: cancelled, customer cancelled."

Mistake 3: No Sequential Numbering

Some freelancers number "by feel" — today 047, tomorrow 053, next week 049. The FTA requires a traceable sequence. If the numbers are all over the place, that is a red flag during an audit.

Solution: Assign numbers in the order in which you issue invoices. If you issue an invoice retroactively, give it the next free number — not one that fits in the middle of the series.

Mistake 4: No Invoice Number for Small Amounts

Some freelancers think: "For an invoice of CHF 50.00 I don't need an invoice number." Wrong. Even small amounts need a unique, sequential number.

Solution: Every invoice gets a number — whether CHF 50.00 or CHF 50,000.00. The law makes no distinction based on amount.

Mistake 5: Invoice Number Changed After Sending

You sent an invoice and later realise the number was wrong. You change the number and resend the invoice. Now you have two invoices with different numbers for the same transaction — and the customer does not know which is valid.

Solution: The invoice number is fixed once sent. If you discover an error, issue a credit note and then a new invoice with a new number. An invoice number that has been sent is never changed.

Automatic Invoice Numbering: How Magic Heidi Saves Time

The simplest solution for all invoice numbering problems is to automate. With invoicing software like Magic Heidi, you no longer have to worry about the invoice number.

How Automatic Assignment Works

Magic Heidi generates the invoice number automatically when you create a new invoice. The format is preset (RE-YYYY-001) but can be customised to your preferences. The software checks which number was last assigned and automatically assigns the next one. You cannot assign a duplicate number, create a gap, or mix up the sequence.

The invoice number is placed in the correct position on the invoice — along with all other mandatory details such as date, VAT rate (8.1% or 2.6%), QR-Rechnung (the Swiss QR-bill), and your customer data. You do not have to think about anything.

What Magic Heidi Handles for the Invoice Number

• Automatic assignment: Every new invoice gets the next free number from the sequential series.
• Configurable format: You choose the format that fits your business — 2026-001, RE-2026-001 or a custom one.
• Gap-free documentation: Every assigned number is saved. During an FTA audit, you have the complete list at the push of a button.
• Credit notes: When you cancel an invoice, Magic Heidi automatically creates the credit note with its own number.
• Year change: On 1 January, numbering automatically restarts at 001 — if you have configured it that way.

  What It Costs

  
  Magic Heidi is available from CHF 25.00 per month — for solo freelancers and small businesses. For comparison: bexio costs from CHF 52.00 per month and offers features you probably never need as a freelancer (inventory management, payroll, webshop). Anyone doing a cheaper than bexio comparison quickly sees: for most self-employed people, Magic Heidi is the better choice. You can find all prices on the pricing page.

  Mini-Story: Sandra, Graphic Designer from Zurich

  
  Sandra, a freelance graphic designer from Zurich, used to create her invoices manually in Word. With 150 invoices per year, numbering was a constant source of stress. Every week she checked: what was the last number? Had she forgotten one? Were all credit notes correctly numbered?
  Since switching to Magic Heidi, she no longer worries about any of it. The software generates the invoice number automatically in the format RE-YYYY-001. For the annual VAT filing, Sandra exports the complete invoice list with all numbers to an Excel file. The filing with the FTA now takes 15 minutes instead of 2 hours.
  "The CHF 25.00 per month paid for itself in the first week," says Sandra. "Just the time I used to spend on numbering was more expensive."

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  Invoice Numbers in International Comparison: Switzerland vs. EU

  
  If you have customers in the EU, you may wonder whether your Swiss invoice number is valid there too. The short answer: yes, but there are a few differences you should know about.

  Switzerland

  
  In Switzerland, the invoice number is a mandatory detail under Art. 26 MWSTV. The format is not prescribed; the FTA only requires uniqueness and traceability. This means: you have maximum freedom in designing the number.
  VAT liability applies from CHF 100,000.00 turnover per year. Below that, you are exempt from VAT and do not have to charge VAT — but the invoice number is still required, as also discussed under VAT for freelancers. Anyone who issues an invoice without VAT still needs a unique, sequential number.

  EU

  
  In the EU, the invoice number is also mandatory under the VAT System Directive (MwStSysRL). The requirements are similar to Switzerland: unique, sequential, traceable.
  One difference: some EU countries have stricter format requirements, especially for electronic invoices and the so-called "sequential invoice number." Italy, for example, requires that invoice numbers be strictly sequential and reported to the Italian tax authority. Germany is more flexible here, but the requirements for traceability are similar.

  What Does This Mean for Swiss Freelancers?

  
  If you as a Swiss freelancer issue invoices to EU customers, your normal Swiss invoice number is sufficient. You do not need to use a special EU format. What matters is that the invoice contains all mandatory details required in the EU — which in practice is mostly covered by the Swiss requirements.
  For a correct Swiss invoice with all mandatory details, you can use an invoice template that already includes all fields — or you use software that handles this automatically.

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  Conclusion: Assigning the Invoice Number Correctly — Without Stress

  
  The invoice number is one of the simplest mandatory details on a Swiss invoice — and at the same time one of the most common sources of errors. The rules are clear: unique, sequential, traceable. The format is your free choice, as long as you stick with it and document every gap.
  If you do three things, you are on the safe side:
  1. Choose a format and stick with it. 2026-001 or RE-2026-001 are proven and simple.
  2. Keep a central list of all assigned invoice numbers — ideally automatically in software.
  3. Document gaps and cancellations. A brief note is sufficient as an explanation for the FTA.
  
  Anyone who implements these three points has nothing to fear at the next VAT audit. And anyone who uses invoicing software like Magic Heidi no longer has to worry about any of these points — the software handles numbering automatically and error-free.
  Start invoicing with Magic Heidi — from CHF 25.00/month →
  Do not get stuck with manual numbering. Try Magic Heidi and see how easy correct invoices can be — with automatic invoice numbers, QR-Rechnung and VAT calculation. The invoice template is already built in, the format is configurable, and the year change happens automatically.

  And if you want to make sure Magic Heidi is the right tool for you: compare for yourself — Magic Heidi is cheaper than bexio and tailored to Swiss freelancers, not to large companies with inventory and payroll.