The 2026 withholding tax key formula, step by step

What the key formula calculates

Withholding tax (bedrijfsvoorheffing) is an advance on your income tax, deducted every month by your employer. The key formula, set each year in Annex III to the Royal Decree implementing the Income Tax Code 1992, turns the month’s pay into a theoretical annual tax, then brings it back to a monthly amount. The monthly scales published by FPS Finance follow from it: payroll software applying the formula and a payroll administrator reading the scales should arrive at the same amount, give or take a few cents.

Indexo applies the 2026 key formula, with the amounts in force on 1 October 2026. The same calculation, for your situation, is laid out in the calculator’s expert mode, further down this page.

The steps, one by one

1. Taxable pay for the month. Gross pay minus personal contributions: 13.07% in National Social Security Office (NSSO) contributions, less the work bonus, for an employee; 11.05% for a statutory civil servant. Taxable benefits (company car, IT equipment) are added.
2. Annualisation. This amount is multiplied by 12.
3. Lump-sum professional expenses. 30% of annual pay, up to €6,070.00 in 2026.
4. Net annual taxable pay. Annual pay minus these expenses.
5. Marital quotient. If you are married or a legal cohabitant and your partner has no earned income, 30% of this amount, up to €13,790.00, is allocated to your partner and taxed separately, at the lowest rates.
6. Basic tax. The progressive scale applies bracket by bracket: 26.75% up to €16,710, 42.80% up to €29,500, 48.15% up to €51,050, 53.50% above €51,050.
7. Tax-free amount. The tax is reduced by €11,170 × 26.75%, i.e. €2,987.98 a year, and by twice that with the marital quotient.
8. Basic withholding tax. The resulting annual tax is divided by 12.
9. Reductions for dependants. Fixed monthly amounts are deducted: €52 for 1 child, €138 for 2 children, €367 for 3 children, €635 for 4 children, then more per child; €52 per other dependant, €166 per care-dependent person aged 66 or over.
10. Fiscal work bonus. For low earners, 33.14% of part A and 63% of part B of the social work bonus are also deducted from withholding tax.
11. Overtime. Where applicable, a withholding tax reduction applies to hours paid with an overtime premium, up to 180 hours a year.

The withholding tax rates are the personal income tax rates (25% to 50%), increased by a flat 7% municipal tax: 25% × 1.07 = 26.75%.

Full example: single white-collar worker, €3,000 gross

Result: €437.87 of withholding tax deducted. After the special social security contribution of €19.24, €2,261.33 net a month remains.

Second example: married, one income, two children, €4,000 gross

The marital quotient (€10,696.92) and the reductions for children (€138.00 a month) bring withholding tax down to €269.18, against €826.70 for a single person with no children on the same gross pay.

The 2026 key formula parameters

What the key formula does not cover

• The special social security contribution: a separate deduction, from 0 to €60.94 a month, calculated on gross pay and household situation.
• Holiday pay and bonuses: they follow the non-recurring withholding tax scale, a single rate based on annual pay (see Bonuses and holiday pay).
• Final tax: it is assessed the following year on all income, with the actual municipal tax and a tax-free amount of €11,550 instead of €11,170 in the 2026 withholding tax. The difference is refunded or claimed (see Tax refund or tax to pay).

Frequently asked questions

What next?

• From gross to net: the calculation explainedThe four steps to net pay, for all employees.
• Tax refund or tax to payWhat the withholding tax deducted will mean at the year-end settlement.
• Proof of accuracyThe engine’s verified cases, to the cent.
• Method and sourcesAll parameters, with their sources.