A nonresident alien's income that is subject to
U.S. income tax must be divided into two categories.
1. Income that is effectively connected with a
trade or business in the United States, and
2. Income that is not effectively connected
with a trade or business in the United
States (discussed under The 30% Tax,
The difference between these two categories
is that effectively connected income, after
allowable deductions, is taxed at graduated
rates. These are the same rates that apply to
U.S. citizens and residents. Income that is not
effectively connected is taxed at a flat 30% (or
lower treaty) rate.