The Physical Presence Test is one of two routes a US citizen or resident abroad can use to claim the Foreign Earned Income Exclusion. It turns on a single mechanical question: were you physically present in a foreign country for at least 330 full days during a 12-month period? Unlike the Bona Fide Residence Test, it ignores your intent and your ties. It counts days, nothing else, which makes it the more predictable of the two for anyone who travels.
The detail that trips people up is the definition of a full day (a continuous 24 hours in a foreign country) and the freedom to slide the 12-month window to whichever span maximises your qualifying days. The advisers I compare notes with on US matters treat the window choice as the real lever. Enter your travel periods below and pick the window to test; the tool counts the full days for you.