Consequences of residing in Spain and not registering as a tax resident
Tax residence is a concept that determines in which country you must pay your taxes. According to article 9 of the Personal Income Tax Law, a natural person is considered to be a tax resident in Spain when one of these requirements is met:
Staying in Spain for more than 183 days during the calendar year.
That the main nucleus or the base of their activities or economic interests, directly or indirectly, is in Spain.
Their non-legally separated spouse and their dependent minor children habitually reside in Spain, unless proven otherwise.
The consequences of residing in Spain and not registering as a tax resident can be serious, since you can incur double taxation (paying taxes in two countries for the same concept) or a tax offense (not paying taxes in the country where you must do it). In addition, you may lose some tax or social benefits that correspond to Spanish tax residents.
To avoid these consequences, it is important that you find out about the tax residence rules that apply in each country and that you prove your situation to the corresponding tax authorities.