Filing Your Belgian Tax Return (Tax-on-web & the Annual Declaration)

Filing your first Belgian tax return sounds worse than it is: for most employees the tax office has already filled in the numbers and you may not have to send anything at all. This guide explains who must file, what the proposed simplified return is, how to file online with Tax-on-web and itsme, the 2026 deadlines, and how the withholding on your payslip is squared up against your real tax bill — including the communal surcharge your Brussels commune adds on top.

Who has to file

If you are a Belgian tax resident — which, in practice, you become once you register at your commune and are entered in the National Register — the tax office expects an annual income tax return (déclaration à l'impôt des personnes physiques / aangifte personenbelasting) covering the previous calendar year. The 2026 return covers income earned between 1 January and 31 December 2025 (this is "income year 2025", "assessment year 2026").

You will fall into one of two situations:

• You receive a blank return to complete — the normal case if you have anything beyond a plain Belgian salary (self-employed income, foreign income, a foreign bank account, certain property income).
• You receive a proposed simplified return — a pre-filled proposal, if your situation is straightforward.

Either way, doing nothing is only safe in one specific case (a correct simplified proposal). If you had Belgian income and received no return at all, do not assume you are off the hook — contact your local tax office.

Not sure whether Belgium even taxes you as a resident on your worldwide income, or only on Belgian-source income? That question comes first and changes everything. See Resident vs Non-Resident Tax in Belgium.

The proposed simplified return

To cut paperwork, FPS Finance sends many taxpayers a proposed simplified return (proposition de déclaration simplifiée / voorstel van vereenvoudigde aangifte) instead of a blank form. According to FPS Finance, you are likely to receive one if you get a salary, a pension, unemployment benefit, or sickness/invalidity benefit and do not have certain other income such as:

• income from self-employed or management activity,
• certain immovable property income,
• foreign income, or
• a foreign account.

The proposal contains what the administration already knows — your salary, withholding tax, and often mortgage or pension-savings data. Two rules matter:

• If the data is complete and correct, you do nothing. In the words of FPS Finance: "If your data is complete and correct, you do not need to do anything. You do not need to confirm or send anything." The proposal simply becomes your return.
• If anything is wrong or missing, you must modify it — online, through an accountant, or on the paper reply form — before the deadline. Miss it and the proposal stands as-is.

Because the proposal only reflects what the tax office already has, check it line by line — newcomers most often find missing deductions (childcare, charitable gifts, mid-year pension savings) that no one reported automatically. You can view and amend it even if you received it on paper: it lives online in MyMinfin › My tax return.

The deadlines for 2026

Your deadline depends on how you file and what you declare. These are the dates published by FPS Finance for income year 2025:

Filing online buys you at least two extra weeks over paper, and much longer if you have self-employed or foreign income. Always confirm the exact date shown inside your own MyMinfin account — it is personalised, and a late return can trigger a fine or a tax increase.

Filing online with Tax-on-web

Tax-on-web is the online return, reached through the MyMinfin portal at myminfin.be. To log in you need a Belgian digital identity — the easiest is itsme, the app used across Belgian banking and government. You can also use your electronic ID card (eID) with a card reader and PIN.

The practical steps:

1. Set up itsme first if you have not already — you activate it via your Belgian bank app or eID. It is the key that unlocks almost every Belgian e-government service. (See our itsme guide.)
2. Go to myminfin.be and log in with itsme (or eID).
3. Open My tax return (Ma déclaration / Mijn aangifte). Your return — or your simplified proposal — appears pre-filled with the data the administration holds.
4. Check every pre-filled figure and add anything missing: deductions, foreign income, extra dependants.
5. Tax-on-web shows an estimate of the tax due or refund as you go — useful for spotting a big error before you submit.
6. Submit. For a joint return, both partners must log in with their own itsme/eID and each click Send — a common reason couples think they've filed when only one has.

Keep the confirmation. Your supporting documents (pay certificates, mortgage attestations, childcare receipts) do not all need uploading, but you must be able to produce them if asked, so file them somewhere safe.

Précompte vs the final assessment

This is the part that confuses almost every newcomer, so it is worth being precise.

The précompte professionnel (professional withholding / bedrijfsvoorheffing) you see deducted on every Belgian payslip is not your final tax. It is an advance — an estimate your employer withholds each month and pays to the tax office on your behalf, based on your gross salary and family situation.

Your annual return is where that estimate is squared up:

1. The tax office calculates your real income tax for the whole year, using the progressive brackets and your actual deductions.
2. It subtracts everything already withheld (your précompte, plus any advance payments).
3. The result lands on your tax assessment notice (avertissement-extrait de rôle / aanslagbiljet), usually months after you file.

If more was withheld than you owe, you get a refund paid to your bank account. If too little was withheld, you get a bill to pay. Because the monthly withholding is a rough estimate, small newcomers' refunds and bills are entirely normal — it does not mean anything went wrong.

For reference, resident income tax runs on federal brackets of 25%, 40%, 45% and 50% for income year 2025, with a basic tax-free allowance (quotité exemptée) of €10,910. Confirm current figures on the official FPS Finance tax rates page, and estimate your own gross-to-net with our Brussels salary calculator.

Common deductions worth checking

The return is your chance to claim reductions that monthly withholding usually ignores. The main ones for individuals (income year 2025, per PwC's Belgium deductions summary):

• Pension savings (épargne-pension / pensioensparen): a 30% tax reduction on up to €1,050 paid in (so up to €315 back), or 25% on amounts between €1,050 and €1,350. You choose one ceiling for the year.
• Childcare costs: a 45% tax reduction on childcare for children under 14, up to a maximum of €16.90 per day (income year 2025). Keep the crèche or childminder's official attestation.
• Service vouchers (titres-services / dienstencheques): in the Brussels-Capital Region, a 15% tax reduction applies on the first 172 vouchers bought per person per year — check the current Brussels service-voucher rules, as the benefit differs by region and was cut in Flanders.
• Charitable gifts: a tax reduction on donations of €40 or more to approved organisations. Note the rate was reduced from 45% to 30% from 2025.
• Mortgage / long-term savings and life insurance: reductions apply but the rules are region-specific and changed in recent reforms — verify your case rather than assuming.

These figures are indexed or reformed year to year. Treat the numbers above as the income-year-2025 position and confirm anything material on the official source before relying on it.

How the communal surcharge is settled

On top of your federal income tax, your commune levies a surcharge — the additionnels communaux (aanvullende gemeentebelasting). Per FPS Finance, it is calculated as a percentage of your federal income tax due — not of your income — and is levied at the same time as your federal tax.

Across Belgium these rates run from 0% to roughly 9%; Brussels communes typically sit around 6–7%, and the exact figure depends on which of the region's 19 communes you live in. You do not file or pay this separately: it is added automatically and shown at the bottom of your tax assessment notice, settled together with the federal amount. This is one reason your commune — set when you register your address — quietly affects your final bill.

Common problems and fixes

• "I got a simplified proposal, so I ignored it." Only safe if it is correct and complete. If a deduction or income is missing, you must modify it before the deadline, or the (wrong) proposal becomes your final return.
• "We filed jointly but only one of us clicked Send." A joint return needs both partners to log in with their own itsme/eID and each Send. Verify both submissions went through.
• "I have a foreign bank account / foreign income — do I still get the simplified return?" No. Foreign income or a foreign account disqualifies you from the simplified proposal; you must file the ordinary return and declare the foreign items (treaty relief usually prevents double taxation, but declaring is mandatory).
• "My refund/bill seems random." It is the gap between the précompte already withheld and your real annual tax. A modest difference either way is normal.
• "I can't log in to Tax-on-web." Almost always an itsme/eID activation issue, not a tax issue. Sort your itsme first; if that fails, MyMinfin also accepts an eID with a card reader.
• Anything genuinely complex — self-employed income, moving mid-year, split residence, the expat regime — is worth a social secretariat or tax adviser. Verify specifics on fin.belgium.be.

Your next step

Set up itsme now if you haven't, then log in to myminfin.be and open My tax return to see whether the tax office has already sent you a proposed simplified return. Read it line by line against your payslips and receipts — and if a deduction is missing, correct it online before 15 July 2026. That ten-minute check is the difference between a clean refund and an avoidable bill.