How is a Nonresident Alien taxed?

A Nonresident Alien is generally taxed only on income from US sources. Nonresident aliens income that is connected with a US business and Capital gains from the sale of US real property interests are subject to tax at regular graduated US rates. Generally investment income from US sources that is not connected to US business is subject to a 30% tax rate. Nonresident aliens are required to file on Form 1040NR. IRS Pub 519 explains how Nonresidents are taxed.