Physical presence test

Under §911(d)(1)(B) you qualify by being physically present in a foreign country or countries for 330 full days in any 12-month period. Unlike bona fide residence it ignores intent entirely — it is arithmetic, which makes it the usual route in the year of a move. The details do the damage: a full day is a complete 24-hour period from midnight to midnight, so partial days of arrival and departure do not count, and time over international waters counts against you. The days do not have to be consecutive, and the 12-month window can start on any day, so the window is chosen to maximise qualifying days and the exclusion is then prorated for the days of that window falling inside the tax year. Form 2350 exists precisely because the window often closes after the normal filing deadline.