Starting a Secondary Occupation in Belgium: 2026 Guide

Who can start a secondary occupation?

It all starts with your main job. You run a self-employed activity alongside work as an employee, a civil servant or an equivalent status. That main job already gives you social rights: pension, healthcare and sickness benefits. As a result, a secondary occupation carries lower social contributions while your income stays modest.

This route suits anyone who wants to test an idea. You keep your salary, but you invoice your first clients under your own enterprise number.

The conditions

Three checks decide whether a secondary occupation is open to you.

Civil servants and teachers face their own thresholds. Your social insurance fund checks them with you. Accountants, architects and estate agents, for example, must also prove their qualifications to their professional body.

The basic management knowledge certificate disappeared in Flanders in 2018. Elsewhere, ask your enterprise counter whether proof still applies.

Read your employment contract first

Start with your contract. An exclusivity clause or a non-compete clause can restrict a secondary occupation. The Employment Contracts Act of 3 July 1978 also imposes a duty of loyalty towards your employer.

In practice, do not approach your employer's clients or use its equipment. If in doubt, tell your employer in writing. A clear agreement prevents friction.

Social contributions in a secondary occupation

Your social insurance fund collects contributions every quarter. At the start, it charges provisional contributions because your real income remains unknown. Later, it adjusts the amount using the net income that the tax authorities report.

The calculation follows two rules.

• Below a threshold that changes each year, the cost stays very low.
• Above it, the fund applies a rate of about 20.5% to your net income.

Amounts and thresholds change every year. Check them with your fund or on the INASTI website. You may also pay more voluntarily, so that a heavy adjustment does not hit you later. Our guide to how social contributions work goes through the figures.

Tax: profits sit on top of your salary

The FPS Finance adds your two incomes together. The progressive personal income tax rates then apply, from 25% to 50%, plus the municipal surcharge. However, your salary already fills the lower brackets. Profits from a secondary occupation therefore often land in a high bracket.

You can still deduct your actual business expenses, with receipts.

• Computer equipment and software.
• Business travel.
• The business share of a home office.
• Training linked to your activity.
• Social contributions you have paid.

Remember advance tax payments too. Without them, a tax surcharge may apply.

Registration steps

Follow this order to start your secondary occupation cleanly.

Below €25,000 of annual turnover, the exemption scheme lets you invoice without VAT. Our article on VAT activation in Belgium helps you choose. The FPS Economy also lists the approved enterprise counters.

Example: Julie, weekend photographer

Julie works full-time at a bank. She wants to photograph weddings on Saturdays. First, she rereads her contract and finds no exclusivity clause. Then she registers with the CBE and joins a fund in the same week. She expects less than €25,000 in turnover, so she opts for the VAT exemption.

In year one, her net income stays modest. Her contributions for this secondary occupation therefore remain low. Yet every euro of profit meets her marginal tax rate. Julie sets aside part of each invoice for tax and the later adjustment.

When the side activity becomes your main job

Your status follows your real situation. If your employment drops below half-time or ends, you become self-employed in a main occupation. From then on, the minimum contributions for a main activity apply, even with low income. So tell your fund straight away.

Many founders make this switch after a few years. Prepare it with a realistic financial plan. Our guide to becoming self-employed full-time sets out the steps.

Common mistakes

• Failing to tell the fund when your salaried hours fall.
• Underestimating tax, since your salary already fills the lower brackets.
• Mixing private and business money in one account.
• Invoicing before your CBE registration.
• Forgetting insurance cover for your activity in case of accidents or disputes.

In summary

A secondary occupation lets you build a business without giving up your salary. You keep your social rights, pay adapted contributions and declare profits together with your salary. With Juristelo, turn your project into a financial plan before you start.