Understand · Payroll glossary
What is the NSSO?
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The NSSO, the National Social Security Office, collects social security contributions from employees and employers, then distributes them among the branches of social security. In 2026: 13.07% (employee contribution of a private sector employee, on gross pay (on 108% of gross pay for a blue-collar worker)). In Dutch: RSZ (Rijksdienst voor Sociale Zekerheid).
Definition of the NSSO
The NSSO is the federal body that collects the contributions deducted from salaries (the worker’s share) and those paid by employers. It then redistributes them to the institutions that pay pensions, health care, sickness benefits and unemployment benefits.
Every quarter, the employer declares its staff’s pay and working time to the NSSO in the DmfA (quarterly social security declaration). On a payslip, the ‘social security contributions’ line means the worker’s share.
The key figure in 2026
Source: Instructions administratives : les cotisations de sécurité sociale, National Social Security Office (NSSO). Value in force on 1 October 2026.
Worked example
At €3,000 gross, a white-collar worker pays 13.07% × €3,000 = €392.10 in social security contributions. A blue-collar worker on the same gross pays contributions on 108% of their salary: 13.07% × €3,240.00 = €423.47. The work bonus then brings their actual deduction down to €304.09.
In Dutch: RSZ (Rijksdienst voor Sociale Zekerheid)
On a Dutch-language payslip (loonbrief), the NSSO is called ‘RSZ (Rijksdienst voor Sociale Zekerheid)’; on a French-language one (fiche de paie), ‘ONSS (Office national de sécurité sociale)’. On Indexo’s English pages: National Social Security Office.
Dutch term taken from: National Social Security Office (NSSO).
Not to be confused with…
- NEO: the National Employment Office pays unemployment, time credit and parental leave allowances; it does not collect contributions.
- Holiday fund: the ONVA/RJV, the National Annual Holiday Office, pays blue-collar workers’ holiday pay.
- Special social security contribution: a monthly deduction on top of social security contributions, from 0 to €60.94 a month depending on your salary and household.
Calculate it for your situation
The four steps of the calculation, with a typical payslip to the cent.
Related terms
- Employee social security contributionsFrom gross to net · in Dutch: werknemersbijdragen
- Employer social security contributionsFrom gross to net · in Dutch: werkgeversbijdrage
- Work bonusFrom gross to net · in Dutch: werkbonus
Sources
Parameters in force on 1 October 2026. Each parameter links to its source, the official one where it exists; a secondary source is flagged as such.
- Instructions administratives : les cotisations de sécurité sociale, NSSO. Cross-checked with: UCM, Securex and the FEB (via the Walloon Public Service) for the basic employer rate in the private sector: 19.88% basic contribution and 5.12% wage moderation contribution, making 25%.
- Formalités obligatoires à l’égard de l’ONSS : DmfA dans le mois qui suit le trimestre, cotisations au plus tard le dernier jour de ce mois, Securex (secondary source). Cross-checked with: UCM, NSSO provisional payments (reference amount of €4,000).
- De Rijksdienst voor Sociale Zekerheid (RSZ), NSSO.