TLDR: If you received a salary in Belgium, you must declare it in France if you are a French tax resident. French employers must withhold tax at source and declare it using form n° 2494-SD. Residents in Belgium with French salaries are taxed in France, but Belgium may calculate additional municipal taxes on the "net frontière" income.
Who Must Declare Belgian Income
You must declare Belgian income if:
- You did not have your habitual residence in Belgium as of December 31, 2008.
- You work for a private employer or a public law entity engaged in industrial or commercial activities.
Eligibility for the cross-border worker regime is assessed annually and does not depend on prior benefits. French civil servants residing in Belgium are taxed exclusively in France only if they do not hold Belgian nationality.
Belgian Residents with French Salaries
Since 2009, Belgian tax residents earning salaries in France are taxed exclusively in France. However, Belgium may calculate additional municipal taxes on the "net frontière" income, i.e., gross income minus the tax already paid in France. This mechanism also applies if the income is exempt in Belgium under the tax treaty.
Procedures for Employers and Employees
Obligations for French Employers
French employers paying salaries to Belgian residents must:
- Withhold tax at source on wages paid.
- Declare the withholdings using form n° 2494-SD (CERFA n° 10325), available on impots.gouv.fr.
- Submit the declaration to the corporate tax office by the 15th of the month following the civil quarter in which the salaries were paid.
Obligations for Employees
Employees must complete a specific form, certified by the relevant Service des Impôts des Particuliers (SIP), and submit it to their employer before receiving their first annual salary payment. If the obsolete "276 Front" form was used, the situation can be regularized through an amicable procedure.
Income to Declare and Tax Calculation
"Net frontière" Income for Belgian Residents
Belgian residents earning salaries in France must declare the "net frontière" income in Belgium, calculated as:
Gross income – Tax paid in France
This amount serves as the basis for calculating Belgian additional municipal taxes.
Exclusions and Limits
- Workers who had permanent residence in Belgium as of December 31, 2008, are not eligible for the cross-border regime from 2009 onward.
- Belgian additional municipal taxes apply even if the income is exempt from Belgian tax under the treaty.
Deadlines and Forms
The only explicitly mentioned deadline concerns French employers, who must file the withholding declaration (form 2494-SD) by the 15th of the month following the civil quarter in which salaries were paid.
Required Documents
The main documents referenced are:
- Form n° 2494-SD (CERFA n° 10325): For employers declaring withholdings on salaries paid to non-residents.