Invoicing as a Secondary Self-Employed Worker in Belgium

Being self-employed as a secondary activity (indépendant complémentaire) is a very popular status in Belgium: it lets you launch a professional activity while keeping your salaried job, and therefore your social security cover. In 2026, Belgium has more than 350,000 secondary self-employed workers. But how do you invoice correctly under this status? What are the obligations around VAT, mandatory invoice mentions and bookkeeping? This complete guide takes you through it step by step.

What Is a Secondary Self-Employed Worker in Belgium?

Legal Definition

A secondary self-employed worker is someone who carries out an independent professional activity alongside a main activity that already grants them sufficient social security rights. This main activity can be:

• A salaried job of at least half-time (minimum 235 hours per quarter in general sectors, or per sector-specific rules)
• A public-sector job (at least 200 hours or 8/10ths of full-time)
• A teaching position (at least 6/10ths of a full timetable)

The secondary self-employed status is governed by Royal Decree No. 38 of 27 July 1967 organising the social status of self-employed workers, and specifically its Article 37.

Steps to Becoming a Secondary Self-Employed Worker

Before you can start invoicing, you must complete the following steps:

1. Register with an enterprise counter (guichet d'entreprise): UCM, Xerius, Liantis, Acerta, Partena or Securex. Cost: around EUR 95 (2026).
2. Obtain a business number (CBE): assigned automatically upon registration.
3. Join a social insurance fund (caisse d'assurances sociales): mandatory, even as a secondary self-employed worker.
4. Register for VAT: with the relevant VAT control office (unless you opt for the exemption scheme).
5. Open a business bank account: mandatory if you operate through a company, strongly recommended for sole traders.
6. Check the necessary authorisations: depending on your activity (access to the profession, itinerant trader's card, FASFC authorisation, etc.).

The VAT Exemption Scheme (Small Business Scheme)

Who Can Benefit?

The VAT exemption scheme is provided for under Article 56bis of the VAT Code. It is available to taxable persons whose annual turnover does not exceed EUR 25,000 (excluding VAT). This threshold, raised to EUR 25,000 (unchanged since 2022), applies in 2026.

How Does It Work?

Advantages and Disadvantages

Advantages:

• Considerable administrative simplification
• More competitive pricing for private customers (no VAT)
• No periodic VAT returns to file

Disadvantages:

• No deduction of VAT on your business purchases
• Seen as less professional by some B2B clients
• You must keep an eye on the EUR 25,000 threshold

What Happens If You Exceed the EUR 25,000 Threshold?

If your turnover exceeds EUR 25,000 during the year:

1. You must immediately switch to the normal VAT scheme
2. You must charge VAT on all transactions from the point the threshold is exceeded
3. You must submit a request to switch to the normal scheme to your VAT control office
4. You can then deduct VAT on your business purchases (including retroactively on capital goods acquired in the previous 5 years, under certain conditions)

Concrete example: Marie, a secondary self-employed graphic designer, has turnover of EUR 22,000 as of 15 October 2026. She receives an order worth EUR 5,000. By accepting this order, her turnover exceeds EUR 25,000. She must switch to the normal VAT scheme and charge 21% VAT on this order and all subsequent ones.

Mandatory Mentions on Your Invoices

Under the VAT Exemption Scheme

Your invoices must include:

1. Your details:

   • Name and surname (or trading name)
   • Address
   • Business number (CBE): BE 0XXX.XXX.XXX
   • VAT number: even under the exemption scheme, you have a VAT number (with the mention "Taxable person subject to the exemption scheme")

2. Customer details:

   • Name or company name
   • Address
   • VAT number (if the customer is a taxable person)

3. Invoice details:

   • Sequential and unique number
   • Invoice date
   • Date of delivery or service (if different)
   • Detailed description of the goods or services
   • Quantity and unit price
   • Total amount

4. Mandatory mention: "Small business subject to the tax exemption scheme. VAT not applicable — Article 56bis of the VAT Code."

Under the Normal VAT Scheme

In addition to the mentions above, your invoices must include:

• The applicable VAT rate (6%, 12% or 21%)
• The VAT amount, broken down by rate
• The taxable base per rate
• The total amount, excluding VAT, VAT, and including VAT
• The date VAT becomes due (if different from the invoice date)

Social Security Contributions for Secondary Self-Employed Workers

Contribution Amounts in 2026

Social security contributions for secondary self-employed workers are calculated on net taxable professional income:

Important: if your net income as a secondary self-employed worker is below EUR 1,865.44 per year (2026 threshold), you pay a minimum contribution of around EUR 90 per quarter (i.e. EUR 360 per year). This contribution is due even if you make no profit at all.

Social Insurance Fund Management Fees

On top of social security contributions, your social insurance fund deducts management fees of around 3 to 5% of the contribution amount.

Bookkeeping for Secondary Self-Employed Workers

Simplified Bookkeeping

If your annual turnover does not exceed EUR 500,000 (excluding VAT), you can keep simplified accounts consisting of:

1. A revenue journal: all receipts, with a reference to the invoice or supporting document
2. An expense journal: all business expenses, with supporting documents
3. A financial transactions journal: bank movements linked to the activity
4. An annual inventory: statement of receivables, debts, stock and capital assets

Business Expenses: Actual Costs or a Flat-Rate Deduction?

As a secondary self-employed worker, you can choose between:

Option 1: Actual expenses
You deduct your real business expenses, backed by supporting documents. Deductible expenses include:

• IT equipment and software
• Office costs (pro-rated if your home is also your workplace)
• Business travel costs
• Phone and internet costs (business share)
• Social security contributions
• Professional training costs
• Professional insurance
• Accountant's fees

Option 2: Flat-rate expenses
The tax authorities apply a flat percentage of expenses to your gross income:

The total flat-rate allowance is capped at around EUR 5,040 (2026 amount).

Practical tip: if your actual expenses exceed the flat-rate allowance, opt for actual expenses. Otherwise, the flat rate is generally more advantageous. Run the numbers with your accountant every year.

Mixed Use of Assets (Private/Business)

The Business-Use Proportion

When you use an asset for both your business and private purposes (home office, car, phone), only the business share is deductible.

Home office: you can deduct part of your housing costs (rent or mortgage interest, utilities, electricity, heating, internet) in proportion to the office's floor area relative to the total floor area of your home.

Example: your home is 100 m² and your office is 15 m². You can deduct 15% of your housing costs as business expenses.

Car: if you use your private vehicle for your secondary activity, you can deduct business travel costs at EUR 0.4280/km (2026 mileage allowance), or record actual costs in proportion to business use.

Expenses Specific to Secondary Self-Employed Workers

Tax Return: How to Declare Your Secondary Income

Personal Income Tax (IPP) Return

Your income as a secondary self-employed worker must be declared in your annual personal income tax return:

• Section XVII: profits from a previous professional activity
• Section XVIII: profits from liberal professions, offices or other gainful occupations

This income is added to your salaried income and taxed at the progressive personal income tax rates:

Note: because your income as a secondary self-employed worker is added on top of your salary, it is often taxed in the highest brackets (45% or 50%). It is therefore essential to properly optimise your business expenses.

Municipal and Regional Surcharges

On top of federal tax, you pay municipal surcharges (ranging from 0% to around 9% depending on the municipality) and regional tax (which varies by Region).

Advance Tax Payments

As a self-employed person, you are expected to make advance tax payments (versements anticipés, Articles 157 to 168 of the Income Tax Code 1992). If you do not make sufficient advance payments, a tax surcharge will apply.

Advance payments are made in 4 instalments:

• Instalment 1: by 10 April at the latest (maximum tax benefit)
• Instalment 2: by 10 July at the latest
• Instalment 3: by 10 October at the latest
• Instalment 4: by 20 December at the latest

The surcharge avoided decreases with each instalment. It is therefore best to pay the maximum amount at instalment 1.

Invoicing Tools Suited to Belgian Secondary Self-Employed Workers

Recommended Solutions

Essential Features

Your invoicing software must be able to:

• Manage the VAT exemption scheme (automatic mention on invoices)
• Allow the switch to the normal VAT scheme with no data loss
• Generate sequential invoice numbers
• Allow the issuing of credit notes
• Export data to your accountant (CODA, UBL, CSV formats)
• Be compliant with Peppol electronic invoicing (mandatory for B2B in 2026)

Common Mistakes to Avoid

1. Not invoicing at all: even a small favour done for a friend must be invoiced if you are registered as self-employed.

2. Forgetting the VAT exemption mention: leaving out this mention can be penalised with a fine of EUR 50 to 250 per invoice.

3. Mixing private and business accounts: use a separate bank account for your activity.

4. Not making advance tax payments: the tax surcharge can amount to 4.5% to 9% of the tax due (2026 rates).

5. Exceeding the EUR 25,000 threshold without acting: failing to switch to the normal VAT scheme results in fines and VAT due retroactively.

6. Forgetting to declare all income: even small cash payments must be declared.

7. Not keeping supporting documents: keep everything for at least 7 years.

Conclusion

Being self-employed as a secondary activity in Belgium offers remarkable flexibility to test an entrepreneurial venture while keeping the security of your main job. However, invoicing and bookkeeping obligations are very real, even for small amounts of income. By following the basic rules — mandatory invoice mentions, tracking the VAT exemption threshold, keeping supporting documents, and making advance tax payments — you will avoid unpleasant tax surprises.

Don't hesitate to consult an approved accountant (an ITAA member — Institute for Tax Advisors and Accountants) to optimise your tax situation and support you through your first steps.

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This article was written by the Espero-Soft team for the blog dedicated to entrepreneurs in Belgium. For personalised advice, consult an accountant or an enterprise counter.