Getting Portugal residency does not automatically make a UAE resident a Portuguese tax resident. But the risk is very real. Portugal can treat you as tax-resident if you spend more than 183 days there in a relevant 12-month period, or even with fewer days if you keep a home in Portugal in conditions showing an intention to use it as your habitual residence. Once you are tax-resident, Portugal generally taxes your worldwide income , not just Portugal-source income. For invest