What is DmfA (Belgium)?
The DmfA (multifunctional declaration) is the quarterly return Belgian employers send to the ONSS/RSZ, reporting pay and working time for every employee. The ONSS uses it to calculate the contributions due.
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Example
An employer with three staff files one DmfA for the quarter listing remuneration and working-time data for each of them. The ONSS then works out the contributions to pay.
How DmfA (Belgium) works in Belgium
The DmfA is filed every quarter and triggers the ONSS calculation of contributions. Payment is also quarterly, although some employers must make advance monthly payments.
New hires are a separate step. They must be notified through the DIMONA system at least one day before they start work.
AccountsOS seeds a representative DmfA reminder for each quarter, set on the 15th of the second month after the quarter ends. The exact due date varies, so confirm it with the ONSS. AccountsOS does not submit the DmfA. Your payroll provider or social secretariat does.
Related terms
The ONSS (Office National de Sécurité Sociale) or RSZ (Rijksdienst voor Sociale Zekerheid) is the National Social Security Office. It collects employee and employer social security contributions in Belgium every quarter.
Payroll withholding tax (précompte professionnel / bedrijfsvoorheffing) is the income tax an employer deducts from wages each month and pays to FPS Finance. Returns are filed monthly through the Tax For All (TFA) portal.
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