Your fiscal domicile will determine where you will be paying taxes. Legally spoken, this should be the country were you actually live for most of the year. A rather simplistic rule of thumb you might come accross online is whether or not you spend more or less than 183 days a year in Portugal. Off course, in a more globalized world, this concept has become somewhat vague and the definition can vary between countries. In most cases other parameters will be taken into account to decide what country you have the most 'durable' relation with. In cases where you spend some time in more than 2 countries, the rule of thumb of 183 days per year just does not work.
When determining your fiscal domicile, the following facts will be taken into consideration:
- The time of your stay in the country (> 183 days / year)
- Home of your partner and children
- The location of the school your children attend to
- Where is your financial capital managed?
- Where do you have your insurances?
- Social connections
- Where do you go for your medical treatments?
- Economical ties and connections
- If you go on a holliday, is it always towards the same country?
- Where do you get your mail?
- Where are you registered?
In case of doubt, it is possible that two countries want to claim your fiscal domicile. In those cases you will have to make your case on why your ties to one country are more durable. If you are experiencing problems with this (and the problem exists between two European countries), you can submit your case to Solvit. This is a free service of the EU that can help you in bureaucratic conflicts between two member states or if your rights as a EU citizen are violated. More information about your domicile and rights as a EU citizen can be found on 'your Europe'.
For Americans and other non-EU nationalities, it is best to contact a lawyer in case of disputes, since this is a matter of international that can be very complex.