Cadastral income and property tax: what do you pay yearly as an owner?

Every year in autumn it lands in your letterbox: the property tax assessment notice. For many owners it's a confusing document based on a figure from 1975. Yet it pays to understand how it works, because there are reductions you have to apply for yourself, and the cadastral income also plays a role in your tax return and in any letting.

What is cadastral income?

The cadastral income (KI) is the estimated annual net rental income of a property, as it would have been in 1975. It was set during the last general revaluation and has since only been adjusted for renovations that affect the value (an extension, an extra bathroom) or for new builds. The KI of an average home lies between 600 and 1,500 euros, which seems low because it reflects the rental value of fifty years ago.

You can find the KI on the deed of purchase, on the assessment notice or via MyMinfin. For a sale, it appears in every listing on ikzoek.immo under "Legal information".

From KI to property tax

Property tax is a regional tax on the indexed KI. The KI is indexed every year (in 2026 by a factor of around 2.2); the region, the province and the municipality each then levy a percentage on top of that (surcharges, or "opcentiemen"). The regional base rate is 3.97% in Flanders and 1.25% in Brussels and Wallonia, but the municipal and provincial surcharges make up the largest part of the bill.

Worked example (Flanders): KI of 1,000 euros, indexed to 2,200 euros. Region 3.97% = 87 euros. Province and municipality combined, for example 1,400 surcharges on that amount = 1,218 euros. Total approximately 1,300 euros per year. In a municipality with low surcharges this could be 900 euros, in an expensive city 1,600 euros. The municipality where you buy therefore partly determines your annual cost; the rates are listed on each municipality's website.

Reductions you can get

• Dependent children: in Flanders a reduction applies from two children registered at the address, granted automatically if the data is correct; check your assessment notice.
• Modest home: 25% reduction if the total non-indexed KI of all your properties in Belgium is no higher than 745 euros and you live there yourself.
• People with a disability or war invalids.
• Energy-efficient new builds or major energy renovations: in Flanders a discount of 50 to 100% for five years, depending on the E-level.
• Unproductiveness: if a property stands empty and unoccupied for at least 90 days through no fault of your own (for example due to a major renovation), you can request a proportional reduction. Vacancy by choice doesn't count, and municipalities actually levy a vacancy tax on that.

You apply for reductions via the objection form or online, within three months of the assessment notice being sent.

The KI in your tax return

For your own home you no longer need to declare the KI; the regions tax it only through property tax. For a second home or a property let to a private individual, the indexed KI, increased by 40%, is added to your income and taxed at your marginal rate. If you let to a company or a professional user, the actual rental income is taxed, minus a flat-rate cost deduction. That difference makes letting to private individuals tax-attractive, as long as the rent is higher than the indexed KI multiplied by 1.4.

The KI when buying

A low KI is an advantage for a buyer: less property tax, and possibly access to the reduction for modest homes. But a low KI on a clearly extended or renovated property is a warning sign: the renovation may never have been declared to the land registry, and the authorities may later reassess the KI, resulting in higher tax. Ask the seller about declared works.

What does this mean for your monthly budget?

Property tax is one of an owner's fixed costs, alongside fire insurance, maintenance and, for an apartment, the syndic. The monthly cost calculation on every property page of ikzoek.immo estimates the property tax based on the KI and the municipality, so you see not just the loan repayment but the full monthly housing cost. For a fair comparison between a home in a city with high surcharges and one in a rural municipality, that can easily make a difference of 50 euros a month.