As a homeowner you can deduct paid mortgage interest from your taxable income. The maximum deduction rate is 37.56% (2026). This only applies to annuity and linear mortgages, maximum 30 years.
The deemed rental value (eigenwoningforfait) is an addition to your income based on the WOZ value. In 2026 it’s 0.35% of the WOZ value. With a WOZ of €400,000 that’s €1,400 added to your income.
When your mortgage is (nearly) paid off, you only pay the deemed rental value without interest deduction. Through the Hillen Act this addition is being gradually introduced (until 2041).
Example: with a €350,000 mortgage at 4% interest you pay €14,000 interest per year. With a deduction of 37.56% you save €5,258 in tax. Minus the deemed rental value, your net benefit is approximately €3,800 per year.
The maximum deduction rate has been phased down gradually over the years, from 52% (2013) to today's basic-bracket rate. This rate is the same for every income level — whether you're in the lowest or highest tax bracket, you deduct mortgage interest at the same percentage.
Groundwerk calculates the deemed rental value and interest deduction automatically from the WOZ value and your mortgage details, so your report shows what a property actually costs you net per month — not just the gross monthly payment.