How do I file payroll declarations in Belgium?
Employers file the DmfA with the ONSS each quarter, file withholding tax monthly through the TFA portal by the end of the following month, and notify new hires through DIMONA at least one day before they start.
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Detailed Explanation
## How to file payroll declarations in Belgium
Belgian payroll involves three separate filings.
## 1. DIMONA for new hires
New hires must be notified through the DIMONA system at least one day before they start work.
## 2. The quarterly DmfA
Employers file a quarterly multifunctional declaration, the DmfA, with the ONSS/RSZ. It reports remuneration and working-time data for every employee. The ONSS calculates the contributions due from it. Contributions are paid quarterly, although some employers have to make advance monthly payments.
## 3. Monthly withholding tax
Payroll withholding tax (précompte professionnel / bedrijfsvoorheffing) is filed monthly through the TFA (Tax For All) portal. The return and payment are due by the end of the month following the payroll month. Payroll for March is due by 30 April.
## Rates in context
Employee social security is 13.07% of gross with no ceiling. Employer social security is about 27%. Personal income tax for 2026 uses federal brackets of 25%, 40%, 45% and 50%, with a basic allowance of €11,180.
## Who does the filing
Most employers use a payroll provider or social secretariat. AccountsOS seeds a representative DmfA reminder on the 15th of the second month after each quarter and monthly withholding tax reminders. The DmfA date varies, so confirm it with the ONSS. AccountsOS does not submit payroll filings.
Source: https://boundlesshq.com/blog/running-payroll-in-belgium/
Real-World Examples
First hire
A company hires its first employee starting on the 1st of the month. It files the DIMONA notification at least one day earlier.
Monthly cycle
Payroll for May is processed. The withholding tax return and payment are due by 30 June.
Quarter end
At the end of a quarter, the employer files the DmfA. The ONSS then works out the contributions to pay.
Common Mistakes to Avoid
- Missing the DIMONA notification for a new hire
- Confusing the monthly tax date with the quarterly DmfA date
- Treating the seeded DmfA reminder as a fixed legal date
- Filing late because the following month is short
Frequently Asked Questions
What is DIMONA?
The notification a new hire must trigger at least one day before starting work.
How often is the DmfA filed?
Every quarter.
Where is withholding tax filed?
Through the TFA (Tax For All) portal, monthly.
When is withholding tax due?
By the end of the month following the payroll month.
Does AccountsOS file payroll?
No. It tracks dates and estimates costs. A payroll provider or social secretariat files.
Practical Tips
- Use a payroll provider or social secretariat if you have employees
- Notify new hires early rather than on the day
- Put both the monthly and quarterly dates in one calendar
- Confirm the exact DmfA date with the ONSS
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