If you are an alien (not a U.S. citizen), you are considered a nonresident alien unless you meet one of two tests: the green card test or the substantial presence test for the calendar year (January 1 – December 31). If you do not meet either the Green Card Test or the Substantial Presence Test, then you are a nonresident alien.
Nonresident aliens are generally subject to U.S. income tax only on their U.S. source income. They are subject to two different tax rates, one for effectively connected income, and one for fixed or determinable, annual, or periodic (FDAP) income.
