Before you start

National register number
A determination of whether you are a Belgian tax resident
itsme or an eID card reader, to use MyMinfin
Your employer's assessment of whether the inbound taxpayer or inbound researcher regime applies

Step-by-step

1
Establish whether you are a Belgian tax resident
Residence turns on where your home and centre of economic interests sit, with entry in the population register creating a rebuttable presumption. Residents are taxed on worldwide income; non-residents only on Belgian-source income, on a different return.
OnlineWho: You
2
Raise the inbound regime — the right one — at contract stage
There are two: the inbound taxpayer regime (BBIB), which requires a minimum gross salary, and the inbound researcher regime (BBIO), which does not but imposes qualification and research-activity conditions instead. Both let the employer pay part of your gross remuneration as tax-free expense reimbursement. The employer applies within a short window after employment begins and there is no route back once it closes. Ask which one your institution intends to use, at the offer.
Via employerWho: Your employerAt hiring
3
Know the brackets and where 50% begins
For income year 2026 the rates are 25%, 40%, 45% and 50%, with the top rate from roughly €48,000 of taxable income and a basic tax-free allowance around €11,180. Employee social security of 13.07% is deducted from gross before income tax is calculated, so budgeting from a gross figure overstates what arrives.
OnlineWho: You
4
Note Leuven's communal surcharge and how it compares
The additional communal tax is a percentage of the income tax you owe, voted by the city and published annually by FPS Finance. Leuven charges 6.7% for assessment year 2026, against 7.0% in Antwerp, 6.9% in Bruges, 6.5% in Ghent, 4.9% in the City of Brussels and 8.0% in Liège, with the national table running from 0% in Knokke-Heist to 9.0% in Mesen. Your registered address on 1 January fixes the rate for that year, and the surrounding Flemish Brabant municipalities each set their own.
OnlineWho: You
5
Check the pre-filled proposal rather than ignoring it
Many employees receive a proposed simplified return instead of a blank one. It still has to be checked and corrected — deductions the administration cannot see, such as childcare, pension savings, charitable gifts or a foreign account, will simply be missing. Accepting a wrong proposal by silence is on you.
OnlineWho: YouLate April to mid-July
6
Declare foreign accounts, insurance and property
Belgian residents must report foreign bank accounts to the National Bank's central point of contact and declare foreign life insurance and foreign immovable property in the return, with foreign property valued on the same cadastral basis as Belgian property since the 2021 reform. Researchers arriving from a previous posting elsewhere in Europe are the group that most often misses this.
OnlineWho: You

Documents you’ll need

National register number and itsme or eID reader
Annual payslip summary (fiche 281.10)
Records of foreign accounts, insurance policies and property
Certificates for pension savings, childcare and mortgage deductions
Any inbound taxpayer or inbound researcher regime confirmation

Things most newcomers don’t know

The researcher regime has no salary minimum, and this is the city where that matters most.

The inbound researcher regime (BBIO) carries the same tax-free expense allowance as the executive version — up to 35% of gross treated as reimbursement rather than pay — but drops the €70,000 minimum salary condition entirely, in exchange for qualification and research-activity conditions. In a city containing a six-hundred-year-old university, one of Belgium's largest teaching hospitals and the world's largest independent nanoelectronics institute, an enormous number of arriving postdocs and research engineers fall inside it on paper. The employer has to apply, on a clock — and a faculty department is not a corporate mobility team.

Source: FPS Finance

The pre-2022 Belgian expat regime no longer exists, and its replacement was rewritten for 2025.

The special regime for foreign executives was abolished on 1 January 2022 and replaced by the inbound taxpayer regime (BBIB) and inbound researcher regime (BBIO). For remuneration from 1 January 2025 the tax-free expense allowance rose from 30% to 35% of gross, the €90,000 annual cap was abolished, and the minimum gross salary condition fell from €75,000 to €70,000, with researchers subject to no salary minimum. Social security did not follow, so the 30% and €90,000 limits still apply for contributions and payroll now diverges from tax. Almost everything written online describes either the abolished regime or the 2022–2024 version.

Source: FPS Finance; professional-firm circulars on the 2025 reform

Leuven's 6.7% surcharge sits mid-table, and the Flemish Brabant municipalities around it differ.

The additional communal tax is levied on the tax you already owe, not on income, and each municipality votes its own rate. Leuven charges 6.7% for assessment year 2026, between Ghent's 6.5% and Antwerp's 7.0%, while the City of Brussels charges 4.9% and Liège 8.0%. In a commuter belt where living in Herent, Bierbeek or Oud-Heverlee is entirely normal, the rate is a real variable in the decision — and it is your registered address on 1 January that fixes it.

Source: FPS Finance — communal tax rates for assessment year 2026

The employer applies for the inbound regime, on a clock, and there is no second attempt.

The regime is claimed by the employer within a defined period of the employment starting. Miss that window and it is unavailable for that engagement, permanently — which for a benefit running up to five years and worth as much as 35% of gross as tax-free reimbursement is an expensive oversight. Large employers that hire internationally know the deadline; a university department, a hospital service or a small spin-out hiring its first foreign specialist may not. Raise it explicitly during negotiation and get the answer in writing.

Source: FPS Finance

Common mistakes to avoid

Never asking about the researcher regime because you assumed you earned too little to qualify for anything.
Relying on anything written about the pre-2022 expat regime.
Letting the employer's window to apply for an inbound regime lapse.
Accepting the pre-filled proposal without adding deductions the administration cannot see.
Failing to declare foreign bank accounts, foreign life insurance or foreign property carried over from a previous posting.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.