DECLARATION OF INCOME TAX RESIDENTS IRPF
You must file a declaration for the Spanish income tax IRPF before the end of June 2018 if you are a resident in Spain.
Fiscal residents in Spain are all residents who live or stay in Spain for more than 183 days per year. This number of days does not have to be consecutive, so if you are in Spain for more than about 6 months (183 days) in total, you must state IRPF.
You can not decide yourself that you do not want it because then you will sooner or later get into trouble with the Spanish tax authorities.
Every resident must report his / her world income, including your income (including pension and AOW) from the Netherlands or Belgium.
Even if you have no further income in Spain, you must still declare your income from elsewhere outside Spain.
Not indicating will lead to dramatically high fines and estimated attacks sooner or later, which means that you have to incur high costs to lower some of the fines and attacks.
Better to make a timely declaration.
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