In Belgium

The cadastral income is a central concept in Belgian property taxation. Attributed to every plot and building, it represents the normal annual net rental income the property could have produced, assessed at market conditions of… 1 January 1975.

This is the Belgian peculiarity: CI values have never been revised since that date. The cadastral reassessment (general update) is provided for by law but has never been carried out since 1980. The 1975 values are simply indexed each year by a coefficient published in the Belgian Official Gazette.

The CI serves two major tax functions:

  • Basis for property tax: the PI is calculated on the indexed CI, to which regional rates and additional centimes apply
  • Basis for the tax return: property income is declared via the CI (not the actual rent) for properties let to individuals for private purposes

How is the CI set?

The CI is determined by the Measurement and Valuation Administration (formerly the Land Registry) of the FPS Finance. It is calculated based on the property’s characteristics in 1975: surface area, number of rooms, condition, amenities, location.

Annual indexation

The indexation coefficient is published each year. For the 2026 tax year (2025 income), it is 2.1763. A CI of 1,200 EUR therefore gives an indexed CI of 1,200 x 2.1763 = 2,611.56 EUR.

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Good to know
The CI almost never corresponds to the actual rent. A property with a CI of 1,200 EUR (1975 value) might be rented at 950 EUR/month in 2026. The CI is a tax fiction, not a current market estimate.

Practical example

Isabelle buys an apartment in Namur. The notarial deed mentions a CI of 900 EUR. Here is how this CI impacts her taxation:

  • Property tax: 900 x 2.1763 (indexation) = 1,958.67 EUR indexed CI. Applied to Walloon + municipal rates = approximately 850 EUR/year in property tax.
  • Tax return: Isabelle lets the property to a couple (individuals, private use). She declares the indexed CI (1,958.67 EUR) increased by 40% = 2,742.14 EUR in her personal income tax return. This amount is added to her other income and taxed at the marginal rate.

If Isabelle let to a company, she would have to declare the actual rent (not the CI), which would be less favourable tax-wise.

Key considerations

Letting to a legal entity. When the tenant is a company, the owner declares the actual rent (not the CI) in their tax return. The difference can be significant: an indexed CI of 2,000 EUR vs actual annual rent of 12,000 EUR.

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Warning
Declaring an incorrect CI or omitting a property from the tax return constitutes tax fraud subject to penalties. The FPS Finance cross-references land registry data with personal income tax returns.