Belgian salary taxed twice as resident and non-resident: what can you do for income year 2023?

If the same Belgian salary has already been assessed under resident income tax, a proposed non-resident assessment may result from duplicate administrative files. The response should establish the correct residence status, identify the earlier assessment and explain why the second taxation is incompatible with it. The appropriate remedy and any refund depend on the individual situation.

Figures below are illustrative and rounded; they concern income year 2023, assessment year 2024, with procedural examples arising in 2026.

Why a BIS number can lead to a second tax file

A person may initially receive a BIS number before being entered in Belgium’s National Register. An employer may use that number for payroll and the annual 281.10 salary statement. Later, the individual may file a resident tax return under a National Register number.

If the records are not correctly linked, a non-resident tax office may identify Belgian employment income under the BIS number without seeing the resident return and assessment. Correspondence may also appear under a different administrative record from the one accessible through the taxpayer’s usual MyMinfin account.

Both identifiers have an eleven-digit structure. The official BIS guidance explains that, when sex is known at creation, the birth-month component is increased by 40. This numbering convention identifies an administrative record; it does not determine tax residence.

A typical case is therefore an employee who settled in Belgium during the year, paid resident income tax and later received a notice alleging failure to file a 276.2 non-resident return. Comparing identifiers and income statements is an essential first step.

Tax residence depends on the facts, not just the residence card

Under article 2, paragraph 1, 1° of the Belgian Income Tax Code 1992 (CIR 92), Belgian residence depends on the establishment of a domicile or, failing that, the seat of wealth in Belgium. National Register registration creates a rebuttable presumption of residence.

The reverse does not automatically follow: delayed registration does not by itself prove non-residence. Relevant evidence includes:

• continuous occupation of a Belgian home;

• leases and an address-history certificate;

• employment and ordinary day-to-day activities;

• personal and economic ties;

• registration applications and the actual register-entry date.

The date a residence card was issued should not automatically replace the date residence was established. For an arrival during the year, the resident taxable period runs from the relevant arrival date to 31 December.

Foreign earnings received before that period must be distinguished from income arising during Belgian residence. Their treatment cannot be decided solely by looking at the calendar-year total.

What if another country also considers the person resident?

Domestic residence rules and treaty residence are separate questions. A home retained abroad can require a treaty analysis, but ownership of that home does not by itself settle residence.

The source analysis discusses article 4 of the Belgium–Hungary convention signed on 19 July 1982. The relevant sequence examines the permanent home, the centre of vital interests, habitual abode and nationality. Where homes are available in both countries, the location of closer personal and economic relations becomes particularly important.

This is a treaty-specific illustration, not a substitute for checking the convention applicable to another country. A foreign tax residence certificate should not be requested simply because a standard form mentions it: first establish which residence position the evidence supports.

When does a second assessment amount to duplicate taxation?

Resident income tax (IPP) and non-resident income tax (INR) have different scopes. Under article 228, paragraph 2, 6° CIR 92, relevant Belgian-source employment income can fall within the non-resident regime.

The central issue is whether the same income is being taxed twice where one taxation legally excludes the other. This is the concept of duplicate taxation addressed in Constitutional Court judgment 67/2022. A change of residence during a year means the relevant periods must also be examined; simply finding both tax regimes in one calendar year does not establish duplication.

Useful supporting documents include the earlier assessment, filed return, salary statement and payment evidence. The administration also needs to understand how the two identifiers relate to the same taxpayer.

Correcting the administrative link is important, but it does not replace a timely response to an active tax procedure.

Which return codes and allowances need checking?

The source analysis identifies the following entries for income year 2023:

Under the non-resident rules discussed in articles 243 and 244 CIR 92, the 75% professional-income condition can be decisive for access to the tax-free allowance. Under article 245, a State surcharge replaces communal tax in the relevant non-resident calculation.

Neither the income classification nor social-security status should be assumed from a BIS number. A Belgian employment contract and social-security deductions are evidence to examine, while the 75% test requires the appropriate worldwide-income comparison.

For illustration, salary and holiday pay of around €7,800, less approximately €2,300 in flat-rate expenses, can produce a materially different result if no tax-free allowance is applied. The source estimated approximately €1,300–€1,450 of non-resident tax including the surcharge, before around €700 in withholding, leaving roughly €650–€750 payable. These are scenario estimates, not a tax quote.

A tax increase may also be considered in an ex officio procedure. The source discusses the 2025 reform on first infringements committed in good faith and notes that the presumption of good faith does not apply in the same way to an article 351 procedure. A waiver must not be assumed automatically.

How code 1199 can change a part-year resident calculation

Under article 174/1 CIR 92, applicable since assessment year 2018, certain annual amounts are prorated when the taxable period is shorter than a calendar year for a reason other than death.

The coefficient is qualifying months ÷ 12. A calendar month counts when its 15th day falls within the taxable period.

For income year 2023, the source uses a basic annual tax-free amount of €10,160 and an annual ceiling of €5,520 for flat-rate professional expenses:

The ceiling is not itself the deductible expense: the underlying expense calculation still applies. The source’s longer-period estimate produced expenses of around €2,350, rather than a deduction equal to the full ceiling.

For someone establishing residence during February, 11 months may count if residence began on or before 15 February, compared with 10 months after that date. The evidence must support the starting date.

In a low-income illustration, using only two months can leave taxable income of around €6,100 and an average rate around 18%, whereas a correctly calculated longer period can place taxable income below the tax-free amount. Withholding of about €700 and an employment-bonus tax credit around €170 may then affect the refund.

The source estimated a refund around €860, rather than a payment around €470, under its assumptions. This is not an automatic entitlement: other taxable income, the precise calculation and the available correction procedure must all be checked.

Other payments require their own tax analysis

A residence dispute does not settle the treatment of every grant or allowance received during the year.

The Council of the European Union’s 2026 traineeship FAQ describes Belgian treatment under which its traineeship allowance need not be declared. FPS Finance separately warns that trainees generally do not benefit from the tax privileges applying to certain international-organisation staff.

These statements concern different scopes. A favourable treatment attached to a particular institutional programme should not automatically be extended to another arrangement. The payer, programme rules and applicable administrative treatment matter; absence of a Belgian tax statement does not itself prove exemption.

Response deadlines and correction routes

An article 351 CIR 92 notice of ex officio taxation announces a proposed assessment. It is not itself the final assessment notice. The source describes a one-month period for written observations, beginning on the third working day after dispatch, and a shift in the burden of proving the exact taxable income.

The response should address residence, the earlier taxation and the records that need linking. Keep copies and evidence of timely delivery. If a MyMinfin response function is unavailable, confirm a usable channel with the office handling the notice. A request to link records does not suspend the response deadline.

As a calendar illustration, for a notice dispatched on 1 September 2026, the source counts 4 September as the third working day and 4 October as the one-month endpoint. It recommends receipt by 2 October 2026 and posting by 28 September 2026, rather than relying on a weekend extension. Those earlier dates are precautionary targets for that example, not universal statutory deadlines. An extension for legitimate reasons should be requested before the period expires.

If observations are rejected, article 352bis CIR 92 provides for a reasoned decision before assessment. Once an assessment is issued, the remedies differ:

• Ordinary objection: the source describes a one-year period from the third working day following dispatch of the assessment notice. An assessment sent in late 2024 would ordinarily have passed that deadline in late 2025; the actual notice and delivery method must be checked.

• Ex officio relief under article 376 CIR 92: a separate remedy for qualifying material errors, duplicate taxation or qualifying new facts or evidence. The relevant five-year period described in the source begins on 1 January of the year the tax was established. For tax established in 2024, that gives 31 December 2028.

An incorrect 1199 entry may support a material-error argument, but an error of legal interpretation is not automatically a material error. Relief is therefore conditional. Resolving the non-resident procedure and correcting an earlier resident assessment are distinct steps; neither should be allowed to run past its own deadline.

If no confirmation arrives, the source suggests checking progress after approximately two months. The Tax Conciliation Service may help where a dispute persists. Silence alone should not be treated as confirmation that a file is closed.

Frequently asked questions

Can Belgium tax the same salary as both resident and non-resident income?

A second assessment may be challengeable where it duplicates taxation that legally excludes it. The income, taxable periods and residence status must be compared; the existence of two files is not enough on its own.

Does having a BIS number mean I am a non-resident?

No. It is an administrative identifier, while tax residence depends on the relevant facts and legal rules.

Can I be a Belgian tax resident before receiving my residence card?

Yes, the facts may establish residence earlier. Housing, daily life, personal and economic ties and registration history can help establish the correct starting date.

How much difference can code 1199 make?

For income year 2023, applying 2/12 rather than 11/12 to the €10,160 basic tax-free amount changes the illustrative amount from roughly €1,690 to €9,310. The final tax effect also depends on income, expenses and credits.

Is a refund automatic once duplicate files are linked?

No. Linking the records, closing a proposed assessment and correcting an existing assessment are separate administrative issues. Each may require evidence and an appropriate procedural request.

Can I still correct an assessment after the one-year objection period?

Possibly, through article 376 relief where its conditions are met. The five-year route is not a general extension for every error or disagreement.

Sources

The following legal provisions and public sources are cited in the underlying analysis. Foreign-language source documents retain their original language.

• Belgian Income Tax Code 1992 (CIR 92): articles 2, paragraph 1, 1°; 174/1; 228, paragraph 2, 6°; 243–245; 351; 352bis; and 376.

• Belgium–Hungary convention of 19 July 1982, article 4; Belgian Senate report on the convention.

• Belgian Chamber of Representatives: legislative document concerning non-resident income tax and article 228.

• Crossroads Bank for Social Security: National Register and CBSS registers.

• BOSA: Where can I find my BIS number?.

• Constitutional Court judgment 67/2022: ex officio relief and duplicate taxation.

• Constitutional Court judgment 92/2019: articles 243–245 CIR 92.

• Council of the European Union: Traineeships FAQ, March 2026.

• Brussels Commissioner for Europe: Personal income tax.

• FPS Finance: Staff of an international organisation.

This article explains a general framework and is not a personalised tax opinion. Tax rules and amounts change from year to year. The correct treatment and available remedies depend on the exact residence history, income, documents and procedural dates.

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