How does this calculator count your days?
The calculator turns your stays into a set of distinct presence days, so overlapping trips are never double counted. Entry and exit days both count as full days, which matches how most countries treat partial days of presence. All math runs on plain calendar dates, so results do not shift with your device timezone.
Pick the counting period that matches the rule you are checking. If you are not sure which one applies, run both: the rolling window is always at least as strict as the calendar year. Background on the rule itself is in the 183-day rule guide.
What is the difference between the two modes?
Calendar-year mode counts your presence days inside a single year, January 1 to December 31, the way countries such as the United States (for state rules) and many European systems frame their threshold. It also projects forward: starting from your projection date, it finds the day a continuous stay would cross 183 days in that year.
Any-12-month mode slides a 365-day window across your whole travel history and reports the worst one: the window holding the most presence days, with its exact start and end dates. Countries and treaty rules that say 183 days in any 12-month period mean this stricter version, and a count that looks safe per calendar year can quietly cross 183 when two half-years stack inside one window.
What does the projection date tell you?
The projection answers one question: if you stay continuously from the projection start date, on which date do you reach 183 days in the selected year? It counts the days you already logged, then fills every remaining day forward until the total hits 183. If even a stay through December 31 stays under the threshold, the calculator says the year is not reachable.
Use it to plan exits: the day before the projection date is the latest you can begin worrying, not the first.