How net pay is calculated in Belgium
A Belgian payslip takes three deductions from the gross salary: 13.07% personal social security (ONSS/RSZ), the withholding tax (précompte professionnel / bedrijfsvoorheffing) and a small special social security contribution (CSSS/BBSZ). The withholding uses the official key formula of the SPF Finances. The calculator applies the version valid from 1 November 2026, which reflects the tax reform of July 2026: a tax-free allowance of €11,550, flat-rate professional expenses of 30% (max. €6,070), tax rates of 26.75% to 53.50% including a flat 7% municipal surcharge, and reductions for dependent children (€684 a year for one child, €1,644 for two).
- Work bonus (bonus à l’emploi / werkbonus): below about €3,400 gross a month the 13.07% contribution is reduced. At the minimum wage of €2,189.81 it is cancelled out entirely. A fiscal work bonus lowers the withholding tax as well.
- Family situation: if your spouse or legal cohabitant has no professional income, 30% of your net taxable income (max. €11,780) is taxed as theirs (the marital quotient). At €4,000 gross a month this raises the regular net from about €2,623 (single) to €3,190 with two children.
- Municipal tax: withholding always assumes 7%. Your commune’s real rate, other household income and deductions only come in with the annual tax bill (avertissement-extrait de rôle).
13th month and double holiday pay
Most white-collar employees (employés/bedienden) get 12 monthly salaries plus a 13th month in December and the double holiday pay (double pécule) of 92% of a monthly salary in May or June, so 13.92 monthly salaries a year. Both extra payments are taxed at special flat rates that depend on your annual pay. On €4,000 a month these are 46.44% on the 13th month and 42.39% on the double holiday pay. The 13.07% deduction on the double holiday pay is charged on 85% of a monthly salary only.
| €4,000 gross a month, single, no children | Per year |
|---|---|
| Gross (13.92 × €4,000) | €55,680 |
| Social security (13.07%) | €7,241 |
| Withholding tax (monthly + special rates) | €12,805 |
| Special social security contribution | €486 |
| Net | €35,148 (regular payslip ≈ €2,623) |
Blue-collar workers (ouvriers/arbeiders) pay 13.07% on 108% of their wage. Their holiday pay comes from a holiday fund (15.38% of the previous year’s wages at 108%) instead of the employer. The calculator approximates this case.
Converting a Belgian hourly wage
Belgian payroll converts hourly to monthly pay with 52 weeks ÷ 12 months: monthly gross = hourly rate × weekly hours × 4.3333. The full-time week is usually 38 hours. For example, €20 an hour at 38 hours is €3,293.33 a month, or €45,843 a year with the 13th month and double holiday pay. The figures follow the official SPF Finances withholding rules and the ONSS work bonus tables.