Days that do not count: European territories outside the Schengen area
Guadeloupe, Greenland, Svalbard and Aruba are not in the Schengen area, though France, Denmark, Norway and the Netherlands are. Those days are not Schengen days.
A traveller who spends three weeks in Guadeloupe believing those were Schengen days will under-count what they have left. One who believes the opposite will cancel a trip they could have taken. Both are the calculator being wrong in the way that matters most.
Several Schengen member states have territories the rule does not reach.
France
None of the French territories outside Europe are part of the Schengen area. A Schengen visa does not admit you to them, and a national visa for them does not admit you to the Schengen area. A trip covering both needs two visas.
That includes Guadeloupe, Martinique, French Guiana, Réunion, Mayotte, Saint-Martin, Saint Barthélemy, Saint-Pierre-et-Miquelon, French Polynesia, New Caledonia, Wallis and Futuna, and the French Southern and Antarctic Lands.
Worked through: you spend 1–20 June in mainland France and 21 June–10 July in Martinique. Only the first stretch — 20 days — counts against your Schengen 90. The Martinique days count for nothing in that calculation.
Denmark
The Faroe Islands and Greenland are part of the Kingdom of Denmark but not part of the Schengen cooperation. A Schengen visa does not give access to either, and days spent there are not Schengen days.
Norway
Svalbard is part of Norway but not part of the Schengen area, so travelling between the mainland and Svalbard crosses an external Schengen border. If you need a Schengen visa for mainland Norway, make sure it permits the entries you will actually use.
The Netherlands
The Caribbean parts of the Kingdom — Aruba, Bonaire, Curaçao, Saba, Sint Eustatius and Sint Maarten — are outside the Schengen area and run their own short-stay visa, which is not valid for the European part of the Netherlands or any other Schengen country.
What this means for counting
When you enter your trips into the Schengen 90/180 Calculator, enter only the days you were actually inside the Schengen area. Days in the territories above are not Schengen days and should not be entered as such.
The reverse trap is just as real: those days are not free. Each territory has its own entry rules, and being admitted to one tells you nothing about the other.
Each country page on DAYOZA that has one of these carve-outs shows it in a "Where this rule applies" section, sourced to that country's own authority: France, Denmark, Norway, Netherlands.
Before you travel: DAYOZA provides informational calculations based on the rules and sources available on this page. Immigration and entry requirements can change. Always verify your eligibility and permitted stay with the relevant official authority before traveling.