The interest paid on a mortgage (that is concluded to finance the purchase or to improve the house) is fully tax deductible if the house is used as your main residence. The expenses related to the conclusion of the mortgage loan are also tax deductible:

- closing fee from the bank (afsluitprovisie)
- notary costs for registering the mortgage (not the delivery of the property itself) including the VAT
- valuation costs
- other costs related to the mortgage

When you have the 30% ruling you can still claim these deductions although it may be possible that because of the 30% ruling your taxable income is taxed at a lower tax rate leading to a lower deduction. But the normal tax rates still apply.

Although the mortgage interest is fully tax deductible, you must pay tax on the so called “deemed rental value” (eigenwoningforfait) which is based on the WOZ value of the property. Compared to the deduction of mortgage interest, this is in most cases a relatively low amount, namely 0,8% of the WOZ value. This WOZ value is made every for years by the local government. They send you a statement. The WOZ value is also mentioned on the local property tax assessments. If you can't find anything contact the local town hall or maybe even your neighbours (if they have exactly the same property).

If you leave the Netherlands and decide to maintain the property and rent it out , you will remain taxable with respect to the Dutch property as a non-resident taxpayer. As the property will no longer be your main residence, the property will become taxable in income tax “box 3”, which means that the mortgage interest is no longer tax deductible and that the net value of the house will be subject to a deemed return levy (resulting in a tax of 1.2% of the net value of the house). On the other hand rent you receive is tax free. So make sure that the rent covers the costs and the interest.