Belgium Fines Homeowners €1.1 Million for Undeclared Renovations
Belgian tax authorities have issued 719 administrative fines totaling over €1.1 million since 2024 to homeowners who failed to declare renovations, extensions, or other modifications to their properties, according to data obtained by the financial newspaper De Tijd from the Federal Public Service Finance (FOD Financiën) and reported by VRT NWS. The crackdown targets undeclared changes that affect the cadastral income (KI) — the notional property value that serves as the basis for property taxation in Belgium.
The Scale of Enforcement
The fines, which range from €250 to €3,000 per cadastral parcel, have escalated dramatically since the system became fully operational. In 2024, just 61 fines were issued during the first year of systematic enforcement. That number surged to 459 in 2025 — a 652% increase — and 199 fines have already been handed out in the first half of 2026, suggesting the annual total may exceed last year’s figures.
The average fine stands at €1,519, while the median — the most common penalty — is €2,000, as detailed in a legal analysis by Certifisc. The fines are tiered based on the new KI value: €1,000 for a KI under €745, €2,000 for a KI between €745 and €2,500, and €3,000 for a KI of €2,500 or more.
What Triggers a Fine?
Under Belgian law, any modification that increases the comfort or potential rental value of a property must be reported within 30 days of completion. This includes building an extension such as a veranda or carport, converting an attic into a bedroom, installing central heating, or adding an extra bathroom. Energy-saving improvements — such as insulation, solar panels, heat pumps, and double glazing — do not affect the KI and do not need to be declared.
The cadastral income itself is a notional value representing the net annual rental income a property would have generated in the base year of 1975, multiplied by an annual indexation coefficient. It forms the basis for calculating property tax (onroerende voorheffing) and property income in personal tax returns.
How Authorities Detect Undeclared Work
The FOD Financiën employs approximately 600 field inspectors who use multiple methods to identify undeclared renovations. Municipalities automatically notify the cadastre when building permits are issued. The tax authority also monitors property listing websites for photos showing renovations not reflected in the KI. Energy subsidy applications trigger automatic notifications, and properties sold with a KI of €750 or less automatically undergo review. Field inspectors also conduct random on-site visits.
Before a fine is issued, homeowners typically receive written warnings and site visits, with an average of five opportunities to provide information about the work, according to KBC Private Banking. Only after this process does an administrative penalty follow.
Enforcement Still in ‘Start-Up Phase’
Francis Adyns, spokesperson for FOD Financiën, told VRT NWS that the number of fines is expected to rise further. “In a number of provinces, the procedure was started somewhat later, meaning that part of the fines from last year are still being collected in 2026,” Adyns said. This suggests the geographic scope of enforcement is still expanding as the system moves from its start-up phase to full operational capacity.
Financial Implications for Homeowners
Beyond the fines themselves, homeowners face potentially significant back-tax liabilities. The Flemish tax administration can go back five years for unpaid property tax. For a homeowner with a mid-range KI (€745–€2,500), the fine alone is €2,000, plus back taxes and interest. The real long-term revenue impact for the government comes from the permanent upward adjustment of KIs, which increases annual property tax bills indefinitely.
Broader Policy Context
This enforcement campaign is part of a broader Belgian government effort to enforce building regulations, recover lost tax revenue from undeclared property improvements, and modernize the cadastral system. The administrative fine system was established by a Royal Decree on 20 September 2023, which entered into force on 22 October 2023, after the legal framework had been in place since January 2021 but lacked implementing conditions.
What Homeowners Should Know
Homeowners who have completed renovation work are urged to declare it promptly through the MyMinfin online portal or via the official form available on the FOD Financiën website. Declarations must be submitted within 30 days of completion. Those who come forward voluntarily may avoid penalties, as the enforcement process includes multiple warnings before fines are imposed.
As enforcement continues to intensify, Belgian homeowners would be well-advised to ensure their property’s cadastral income accurately reflects its current state — before the tax authorities come knocking.