Does the 183 day rule reset every calendar year in Portugal?

A lot of countries run a plain calendar year count. Portugal does not, and the difference decides real tax bills.

What the rolling window means

The test is more than 183 days, consecutive or not, in any 12 month period starting or ending in the fiscal year concerned. Take an arrival on 1 October 2026 with a continuous stay to 15 June 2027. Neither calendar year reaches 183 days on its own. The 12 month period from 1 October 2026 does, comfortably, and it ends inside the 2027 fiscal year, so residency is triggered. Because that same window began in 2026, the 2026 fiscal year is in scope too.

How the days are counted

A day counts when it includes a night spent in Portugal, complete or partial (article 16(2) CIRS), so a day trip with no overnight stay does not count. A Friday evening landing and a Sunday morning departure is therefore two days, the Friday and the Saturday, because a night falls between them. Transiting an airport without leaving the international zone does not count either. Days do not have to be consecutive: four separate six week stays inside one rolling year add up the same way as one long stay.

The second trigger has no counting at all

Even a count that stays safely under the line does not settle it. Keeping a dwelling in Portugal in conditions that show you intend to occupy it as your habitual home makes you resident on its own, whatever the day total says. Anyone who signs a twelve month lease for a residence visa file is inside the reach of that test.

If you get the count wrong

The tax authority can assess back tax, interest and penalties on worldwide income for years in which you were in fact resident, so a count kept loosely across a border move is worth redoing properly.

Leave By Check counts a planned stay with the arrival day as day one, and when do I become a tax resident sets out both tests side by side.