Complementary self-employed: the short answer
You are complementary self-employed in Belgium when you run a self-employed activity next to a salaried job of at least half-time. In 2026 you pay no social contributions below €1,922.16 of annual net income, then 20.5% of that income, with a minimum of €98.51 per quarter. You need a company number, a social insurance fund and, in most cases, a VAT number.
In short:
- Main condition: a salaried job of at least half-time, or an equivalent situation (unemployment, incapacity, pension).
- 2026 contributions: €0 below €1,922.16, 20.5% above (official 2026 scale).
- Rights: at the reduced rate, your contributions open no extra rights, including no self-employed pension.
- Alternative: an umbrella company spares you the bookkeeping and paperwork. It costs more on small volumes, and we look at each request case by case.
Who can be self-employed on a complementary basis?
You qualify if your main activity is salaried or public-sector work, or a benefit replacing that work. The conditions are set by INASTI, the national institute for the self-employed.
Situations that qualify
| Your main situation | Condition |
|---|---|
| Employee | At least half-time (half the hours of a full-time job in your sector) |
| Civil servant | At least half-time, 8 months or 200 days a year |
| Tenured teacher | At least 6/10 of a full timetable |
| Unemployment, incapacity | Replacement income at least equal to the minimum single self-employed pension |
| Retired | Entitled to a retirement or survivor's pension |
Below half-time?
Below these thresholds you are in principle self-employed as a main activity, with much higher contributions: at least €890.42 per quarter in 2026. One exception has existed since 1 July 2023: the "article 37" assimilation, on request, if your self-employed income stays below €9,101.26 a year.
What do social contributions cost in 2026?
You pay 20.5% of your net professional income, unless it stays below €1,922.16 a year. The scale is set every year and published by Belgian Social Security.
The 2026 scale
| Annual net self-employed income | Contribution |
|---|---|
| Below €1,922.16 | €0 |
| €1,922.16 to €75,024.54 | 20.5% (minimum €98.51 per quarter) |
| €75,024.54 to €110,562.42 | 14.16% on that band |
These amounts exclude your social insurance fund's management fee.
Three worked examples
Calculated with the 20.5% rate of the 2026 scale:
- €1,500 net income over the year: €0.
- €5,000: €1,025 a year, about €256 per quarter.
- €12,000: €2,460 a year, or €615 per quarter.
Provisional first, adjusted later
In your first year you pay the provisional minimum. After that, provisional contributions are based on your income from three years earlier. When the tax office passes on your actual income, usually one to two years later, your fund adjusts: you pay the difference or get a refund (INASTI). Set aside about 20% of your income from day one so the adjustment doesn't catch you out.
What your contributions don't buy
At the reduced rate you build no extra rights: your social protection stays that of your main job. You build no self-employed pension rights until you contribute at the same level as a main-activity self-employed person (INASTI).
How to become complementary self-employed: the steps
Plan four steps before your first invoice. They are listed on business.belgium.be.
- Register with the Crossroads Bank for Enterprises through an approved business counter. Expect about €111.50 in fees.
- Activate your VAT number. If your turnover stays below €25,000 a year, you can apply for the VAT exemption scheme: you don't charge VAT, and you don't recover it either.
- Join a social insurance fund before you start. It is compulsory.
- Inform your health insurance fund.
Basic business-management knowledge is no longer required in Flanders, Brussels (since 15 January 2024, per economie-emploi.brussels) or Wallonia (since 1 October 2025). Regulated trades still have their own skill requirements.
Tax: your income is added to your salary
Your self-employed profit is added to your other income for personal income tax. With a good salary it is taxed at your marginal rate, the highest band you reach. Deductible-expense and advance-payment rules are changing with the ongoing tax reform: have an accountant check your case.
Careful if your client is your employer
Invoicing your own employer, or a former employer, as a self-employed person is risky. If in practice they organise your work and control your hours, the relationship can be reclassified as an employment contract. The criteria are described by the Federal Public Service Employment.
Complementary self-employed or umbrella company?
For a small activity next to your job, complementary self-employment usually costs less. An umbrella company makes sense when you want no paperwork at all, or when you are preparing to go full-time.
The comparison
| Complementary self-employed | Umbrella company (with us) | |
|---|---|---|
| Paperwork | Company number, VAT, social fund, bookkeeping | None: we invoice and issue your payslip |
| Main cost | 20.5% contributions (€0 below €1,922) | €900/month flat below €10,000 monthly invoicing, 9% above, plus contributions on salary |
| Invoicing | You invoice yourself, with or without VAT | We invoice your client |
| Status | Self-employed next to your job | Employee of the umbrella company |
| Best for | Small volumes, a long-term side activity | No time for admin, testing before leaving your job |
What our fee scale means for a side activity
Our fees are the same for everyone and are not negotiable. Do the maths before you choose:
- 3 days a month at €450: you invoice €1,350 and the €900 flat fee applies, two thirds of your invoice.
- 4 days a month at €600: you invoice €2,400 and the €900 flat fee still applies, 37.5%.
- 20 days a month at €500: you invoice €10,000 and our fee drops to 9%. That's full-time, not a side activity.
Our view: if your side activity stays modest, register as complementary self-employed. Contributions are low and a few hours of bookkeeping per quarter are enough. Our €900 monthly flat fee below €10,000 of invoicing makes an umbrella company expensive for a few days a month. It makes sense when your activity gets close to full-time, or when you are preparing that move and want to handle neither VAT nor bookkeeping. We look at these requests case by case.
In Belgium, umbrella employment is not a status defined by law: it is a salaried relationship with a company that invoices your assignments. We explain when it is lawful in our guide to umbrella employment in Belgium.
What if you leave your job?
Once your activity becomes your main one, your self-employed contributions rise to at least €890.42 per quarter in 2026. That's usually the moment to compare seriously with an umbrella company. Run both options through our Belgium umbrella salary calculator, then read our umbrella employment for freelancers comparison.
Complementary self-employment and unemployment benefits
You can keep a side activity while receiving benefits, under strict conditions set by ONEM, the national employment office:
- the activity must have run for at least 3 months, next to your salaried job, before you claim benefits;
- you declare it on forms C1 and C1A;
- on weekdays you carry it out before 7 am and after 6 pm;
- your daily benefit is reduced by the part of your daily income above €18.44 (amount from 1 September 2026).
If you start while unemployed, look at the "Tremplin-indépendants" scheme: 12 months to test a side activity while keeping your benefits, under conditions.
Frequently asked questions
Is there a maximum income for complementary self-employed?
No income ceiling makes you lose the status: it depends on your main job, not on your earnings. Above €17,374.08 of annual net income, however, you contribute as much as a main-activity self-employed person.
How much does complementary self-employment cost per quarter?
In 2026: €0 below €1,922.16 of annual income, then 20.5% of income, with a minimum of €98.51 per quarter. Add your social insurance fund's fee.
Can I be complementary self-employed with a full-time permanent contract?
Yes, it's the most common case. Check your employment contract: an exclusivity or non-compete clause can limit which clients you may serve.
Do I need a VAT number?
Usually yes, but below €25,000 of annual turnover you can apply for the exemption scheme and not charge VAT.
Can an umbrella company replace complementary self-employment?
It can spare you the paperwork, but it costs more on small volumes. We look at these requests case by case: ask for a personalised simulation, answer within 24 hours.