Belgian payroll in 2026: Dimona, DmfA and the précompte professionnel

Belgian payroll pays money to two public bodies and reports to them on three rhythms. Social security, both the employee’s and the employer’s share, is paid to one collector, the ONSS (RSZ). Income tax withheld from pay, the précompte professionnel (bedrijfsvoorheffing), goes to the FPS Finance. Everything else on the payslip is either the employee’s net pay or a benefit.

The three rhythms are easy to remember once you see them side by side. The Dimona is event-driven: it is filed whenever someone starts or stops working. Withholding is a monthly calculation tied to each pay run. The DmfA is quarterly, and it is the declaration in which the ONSS sees every worker’s pay and working time for the quarter.

The payroll also needs a few facts about each employee before the first run: the national number or another identifier for the Dimona, bank details, and household situation, which the précompte and the special levy both depend on. A change during the year, such as a marriage or a new child, can alter the withholding, so employees should know to report it promptly.

None of it can start without an employer number, which the ONSS issues after an online identification called WIDE. The same door is open to a foreign company that has no establishment in Belgium. Most employers then appoint a social secretariat to run the calculations and filings, and an employer of record does the equivalent for the people it employs.

The Dimona (déclaration immédiate / onmiddellijke aangifte) is the electronic notice that tells the ONSS a person has started working for an employer. It is compulsory for every employer and must be made before the worker starts, not on the first payday and not at the end of the first week.

A second Dimona closes the record when employment ends. Between the two, the declaration does a job that used to belong to a paper personnel register, which most employers no longer need to keep. It also means the list of people declared through Dimona should always match the list of people actually working.

For payroll teams the lesson is to treat the Dimona as part of hiring rather than part of the monthly run. A contract signed on a Friday for a Monday start needs its Dimona over the weekend gap, so the simplest habit is to file the declaration on the day the start date is agreed. The ONSS Dimona pages describe the online service and its fields.

Each month the payroll works down from gross pay in a fixed order: employee social security, then withholding tax, then the special levy. What is left is net pay, which goes to the employee’s account with a payslip showing every step.

• Employee ONSS, 13.07%. Taken from every euro of gross pay, it splits into 7.50% for pensions, 3.55% for healthcare, 1.15% for sickness benefits and 0.87% for unemployment. On €4,500 a month the deduction is €588.15.
• Précompte professionnel. Calculated on pay after social security with the statutory formula published as an annex to the royal decree that implements the Income Tax Code. The result depends on household situation, so two people on the same salary can see different amounts.
• Special social security contribution. The third deduction (cotisation spéciale de sécurité sociale in French, bijzondere bijdrage voor de sociale zekerheid in Dutch) is withheld monthly on a scale linked to quarterly pay and household status. Someone taxed individually pays no more than €182.82 a quarter, €731.28 over a year.

Two of these are provisional. The withholding tax is an advance on the employee’s final income tax, and the special contribution is settled on the annual assessment too. Income earned in 2026 belongs to assessment year 2027, so a Belgian employee’s tax for this year is only finally settled in the following one.

The payslip itself is one of the compulsory social documents, along with the individual account the employer keeps for each worker. A clear payslip saves more questions than any explanatory email.

On top of gross pay, a private-sector employer pays ONSS contributions of 25.00% for category 1 workers in 2026. Of that, 19.88% is the basic rate and 5.12% the wage moderation charge, and with no ceiling in the system the rate bites on the last euro of a senior salary as much as on the first. On a €4,500 month that is €1,125, which, with the employee’s €588.15, means €1,713.15 reaches the ONSS for that one salary.

The 25.00% is spread across branches of the social security system: pensions take 8.86%, healthcare 3.80%, sickness benefits 2.35%, unemployment 1.46%, occupational diseases 1.00% and work accidents 0.30%. Small special contributions and sector fund contributions set by the joint committee are added on top, and their exact level depends on the employer’s sector and size.

Lower salaries receive an automatic structural reduction (réduction structurelle / structurele vermindering), worked out per quarter. Under the formula in force from 1 January 2026, it falls to nil once quarterly pay exceeds €11,458.57, about €3,820 a month, so most professional salaries do not benefit. Because one office collects both sides, the employer pays the two shares in a single flow.

Our guide to employer cost in Belgium adds insurance, the prevention service and the yearly bonuses to these contributions for a full annual budget.

Three months each year carry payments that follow their own rules, and a payroll that treats them like ordinary salary will get them wrong.

June. White-collar employees with a full reference year receive the double pécule de vacances, 0.92 of a monthly salary, sometimes a month earlier in May. Ordinary ONSS does not apply to it on either side. Instead, 13.07% is deducted from the employee on 85/92 of the sum, and the 7/92 balance is paid gross. PC 200 staff also receive the annual premium, €330.84 in 2026, which is ordinary pay. Withholding on the holiday pay uses a special rate for exceptional payments. On a €4,500 salary, the double holiday pay is €4,140 and the special deduction €499.93, so June gross, with the premium, comes to €8,970.84.

December. The 13th month under PC 200 is one month’s pay for anyone with half a year of service by then, and a proportional share for newer staff. It attracts normal ONSS on both sides and its own special withholding rate.

January. PC 200 salaries are indexed automatically. In 2026 the increase was 2.21%, applied to scales and to actual pay. Next January brings a new wrinkle: the index centimes. For salaries above €4,000 a month (full-time basis), the slice over that line will be indexed less until a 2% moderation is absorbed, and payroll must also calculate the temporary employer levy that the ONSS charges on the saving.

Departures add a fourth exception at any time of year. The last payslip settles holiday pay for the months already worked, at 7.67% single plus 7.67% double of that year’s gross.

Every quarter the employer sends the DmfA, the multifunctional declaration, giving the ONSS the pay and working-time data for each worker. Its deadline is the last day of the month that follows each quarter.

• July to September 2026: due by 31 October 2026.
• October to December 2026: due by 31 January 2027.
• January to March 2027: due by 30 April 2027.

The fourth-quarter return tends to be the fullest for white-collar staff, because it carries the December 13th month alongside three ordinary salaries, while the second quarter holds the double holiday pay and the PC 200 premium. Plan the reconciliation time for those two returns accordingly.

The DmfA is where the year’s payroll decisions become visible to the social security system. Holiday pay, bonuses, working time and any reductions all appear per worker, so an error made on a March payslip resurfaces in the first-quarter return at the end of April. Reconciling each declaration against the quarter’s payslips before it goes out is the cheapest control a payroll team has.

If you employ through Employer of Record Belgium, the DmfA is filed under our ONSS registration as the employer, and you see the result as part of your monthly and quarterly reporting rather than as a separate task.

When someone leaves during the year, the year-end work for that person happens early. The final pay includes exit holiday pay, an exit Dimona closes the record, and the leaver takes away three documents: a C4 for the unemployment office, a holiday certificate that the next employer will ask for, and a certificate of employment.

Once the income year closes, every employee receives form 281.10, an annual tax slip showing pay and withholding for the income year. The employee uses it for the personal tax return, and the FPS Finance then issues the final assessment, which settles the difference between the tax withheld and the tax actually due.

For income year 2026 the federal scale charges 25% on the first €16,720 of taxable income, 40% on the slice to €29,510, 45% on the slice to €51,070 and 50% on everything beyond. A communal surcharge, set by each commune, is added to the result, so two colleagues on identical salaries can pay slightly different tax depending on where they live.

These rates explain why the monthly précompte professionnel can feel heavy on a mid-range salary: the 45% band starts at €29,510 of taxable income. In our 2026 worked example, a €4,500 salary leaves the employee about €38,100 net for the year, roughly 60.5% of total gross.

If you are about to run Belgian payroll for the first time, the sequence from signed contract to first payslip is traced in the EOR process in Belgium, and EOR explained for Belgium shows which of these filings move to the EOR when it holds the contract.