What is deducted from a gross salary in Belgium?
Three things, in this order. First, the personal social security contribution of 13.07% of your gross salary, collected by the National Social Security Office. Then the withholding tax, an advance on your income tax. Finally, a special social security contribution, withheld monthly and settled in your annual tax assessment.
The withholding tax is not a single rate. It is calculated with a key formula published every year by the SPF Finance, and it depends on your income, your marital status and your dependants.
What is the work bonus, and who gets it?
The work bonus is a reduction of the 13.07% contribution for lower salaries. It can cancel the contribution entirely at the bottom of the scale and is phased out as pay rises.
In 2026 the thresholds for white-collar employees run up to roughly €3,300 gross a month, according to the ONSS instructions. Above that, you pay the full 13.07%. Most experienced IT and engineering profiles are above it.
Why can two offers with the same gross give a different net?
Because Belgian packages are built around the gross salary, not inside it. Meal vouchers, eco vouchers, a company car or mobility budget, a hospitalisation plan or a group insurance are taxed differently, and some barely at all.
A company car is not free either: it adds a taxable benefit in kind to your gross, which raises your withholding tax. Comparing offers on the gross alone misses all of this. Ask for the full package, then compare the gross and net side by side.
How can you estimate your own net salary?
Use the official calculator of the SPF Finance for the withholding tax, or a payroll provider’s simulator. Enter your real household situation, because it changes the result.
Then check your first payslip. The lines follow the same order: gross, minus 13.07%, minus withholding tax, minus special contribution, plus any net allowances. If something does not match the offer, the payslip is where it shows first. Ask for the full package before accepting any of the IT and engineering roles currently open, and run this calculation on it.
