When you move to Portugal, you generally become tax resident if you spend more than 183 days in the country in any 12-month period, or if you have a home here in conditions that suggest you intend to keep it as your usual residence.
Part-year residency in the year you move
In the year you arrive, you can be treated as resident only from the day you settled in Portugal. Before that date, you’re taxed as a non-resident, and only on income earned here.
Foreign income
As a resident, you declare your worldwide income in Portugal. Double taxation treaties stop the same income being taxed twice, usually through a credit for tax already paid in the other country.
Deadlines
The personal income tax return is filed between 1 April and 30 June of the year after the income was earned. Updating your address with the Tax Authority as soon as you move avoids problems with your tax residency.