Part-time work calculator: net pay online
Enter your full-time gross salary and pick your new working-time arrangement. You immediately see the indicative net for both situations and the difference per month and per year. Nothing is stored.
Last updated: · Free · No account · No email
Result
Net full-time (indicative)
€2,420 per month
€3,500 gross
Net part-time (indicative)
€2,078 per month
€2,800 gross
You keep 86 % of your full-time net, at 80 % of the gross salary
- Difference per month
- €341
- Difference per year
- €4,097
Composition of the net (part-time)
- Employee social security contribution
- − €366 per month
- Lump-sum professional costs
- €6,070 per year
- Taxable income per year
- €23,138
- Personal income tax (federal)
- − €329 per month
- Municipal tax
- − €26 per month
- Effective deduction
- 25.8 %
How is this calculated?
- Gross part-time salary = gross full-time salary × percentage.
- Employee social security = gross yearly salary × 13.07 %.
- Lump-sum professional costs = 30 % of the salary after social security, capped at €6,070 per year.
- Tax = progressive brackets on taxable income, reduced by the tax on the tax-free allowance of €11,180.
- Municipal tax = federal tax × municipal percentage. Net = salary after social security − tax − municipal tax.
Assumptions of this calculator
- Rates and amounts of assessment year 2027 (income 2026), as published by the Belgian tax administration; to be updated yearly.
- Single employee without dependants, without work bonus, without other income or deductions.
- Holiday pay, end-of-year bonus, meal vouchers and other benefits are left out; they usually fall proportionally.
- The withholding tax on your payslip may differ from the final tax; this is a yearly approximation, not a payslip.
Download the Excel version
Want to adjust the calculation yourself? Download the Excel version of this tool.
In short
Part-time work means your working hours are lower than those of a full-time employee in your company; your gross salary falls proportionally, but your net salary falls less because personal income tax is progressive.
Sources & calculation method
This is how the calculation is built:
- Gross salary per regime = full-time gross × percentage (100, 90, 80, 60 or 50%). That is proportional; a 4/5 regime gives 80% of the full-time gross.
- Employee social security contribution = gross salary × 13.07%. Taxable salary is gross minus that contribution. Reductions such as the work bonus for low salaries are not in the model.
- Withholding tax = taxable salary × the percentage you set per regime. The model deliberately uses an effective percentage instead of the official scales; those depend on your family situation and change every year.
- Indicative net salary = taxable salary − withholding tax. Difference per month = net full-time − net part-time; per year = difference × 12. Disappearing costs and an optional interruption allowance are deducted from that difference.
- Double holiday pay and the end-of-year bonus are calculated proportionally: full-time amount × working regime. The file does not convert them to net.
Assumptions
- The employee social security contribution of 13.07% applies to private-sector employees: 7.50% pensions, 3.55% healthcare, 1.15% sickness and disability benefits and 0.87% unemployment, according to the administrative instructions of the RSZ/ONSS.
- Withholding tax is an assumption you enter yourself. The real amount depends on your family situation, dependent children and the scales of the year; the final tax follows through your personal income tax return.
- Holiday pay and the end-of-year bonus are calculated proportionally. Some sectors apply other rules, for example blue-collar workers who receive their holiday pay through the RJV/ONVA.
- The model assumes a single gross salary, without meal vouchers, benefits in kind or bonuses. You can include those separately in the household budget.
Limitations
- The file is not a payroll calculation and does not replace a simulation by your employer or payroll provider.
- It does not calculate the RVA/ONEM interruption allowance for time credit or thematic leave; you enter that amount yourself.
- The effect on your pension build-up is not quantified; some forms of time credit are assimilated, plain part-time work is not.
Sources
- Sociale Zekerheid – Administratieve instructies RSZ: de socialezekerheidsbijdragen
Used for: Table of contribution percentages per social security branch; the employee share in the private sector (7.50 + 3.55 + 1.15 + 0.87) adds up to 13.07%.
Accessed: September 24, 2026
- FOD Financiën – Belastingtarieven personenbelasting
Used for: The progressive system with tax brackets from 25% to 50%, the reason net pay falls less than gross pay.
Accessed: September 24, 2026
- FOD Werkgelegenheid, Arbeid en Sociaal Overleg – Deeltijdse arbeid
Used for: What part-time work means legally and which rules apply to the contract and schedules of part-time employees.
Accessed: September 24, 2026
- RVA – Tijdskrediet (privésector)
Used for: The right to time credit with the employer and to interruption allowances from the RVA/ONEM, as an alternative to a plain contract reduction.
Accessed: September 24, 2026
This page and the file were last updated on September 24, 2026. Legislation and rates may have changed since.
Frequently asked questions
How much net do I lose if I go 4/5?
Less than 20%. Your gross salary falls by a fifth, but your net falls less because personal income tax is progressive: the highest slice of your salary is taxed most heavily and that is exactly the slice that disappears. In the example above, gross falls by €700 per month but the indicative net by €316.43, or 13.7%. The exact figure depends on your salary, your family situation and the withholding tax scales; ask your employer for a simulation.
What is the employee social security contribution in Belgium?
Private-sector employees pay 13.07% of their gross salary to social security. That percentage is the sum of four branches: 7.50% for pensions, 3.55% for healthcare, 1.15% for sickness and disability benefits and 0.87% for unemployment. The employer withholds it and passes it on to the RSZ/ONSS. For low salaries there is a reduction, the work bonus, which the file does not include. The percentages are published in the administrative instructions of the RSZ/ONSS.
Does my holiday pay drop if I work part-time?
Yes. Double holiday pay for white-collar employees is calculated on the salary of the holiday reference year, meaning the year before the holiday. If you work 4/5 for a whole year, the year after you receive about 80% of the double holiday pay you would have received full-time. The number of holiday days also falls proportionally. The same applies to the end-of-year bonus in most sectors. In the year of the switch itself you often still see a mixed amount.
What is the difference between part-time work and time credit?
With plain part-time work you change your employment contract, usually permanently, and receive only your lower salary. Time credit (tijdskrediet or crédit-temps) is a temporary reduction or interruption while keeping your full-time contract, subject to seniority conditions and with a motive such as caring for a child or following training. If you meet the conditions, you then receive an interruption allowance from the RVA/ONEM on top of your part-time salary. Parental leave and other thematic leaves work in a similar way. The conditions are on the RVA/ONEM website.
Does part-time work affect my pension?
Yes. The employee pension is calculated on the length of your career and your salaries; a lower salary therefore means a lower pension for those years. Periods of time credit with a motive and thematic leave are assimilated under certain conditions, so they count as if you had worked. Plain part-time work without an allowance is not assimilated. Check your personal situation on mypension.be and ask the Federal Pensions Service.
Osko Consult
Want more insight into your financial situation?
Osko Consult builds overviews, calculators and dashboards to order, also for small organisations and self-employed people. An Excel that does exactly what you need, instead of a template that almost fits.
Related tools
- Excel template
Belgian personal income tax calculator in Excel
Estimate the Belgian personal income tax on your salary or profit: tax brackets, personal tax allowance and municipal tax for assessment year 2026, with the assessment year 2027 figures already in the parameter sheet.
Individuals · Self-employedFree - Excel template
Household budget template in Excel
Line up your income, fixed costs and variable spending month by month and see straight away how much is left to save, with a comparison between budget and actual.
IndividualsFree - Excel templateOnline calculator
Car cost calculator in Excel
Work out what your car really costs per year, per month and per kilometre: depreciation, insurance, road tax, fuel or charging, maintenance and more.
Individuals · Self-employedFree - Excel templateOnline calculator
Loan repayment calculator in Excel
Work out your monthly payment, see in a full repayment schedule how much interest and capital you pay each month, and find out what a loan costs you over its whole term.
Individuals · Self-employedFree