Determining tax residency status is critical for non-U.S. citizens with financial ties to the United States. The Internal Revenue Service (IRS) classifies individuals as non-resident aliens for tax purposes unless they meet one of two key tests: the Green Card Test or the Substantial Presence Test.

Under these rules, a person who satisfies either test in a given calendar year is considered a U.S. tax resident. The Green Card Test applies to lawful permanent residents, while the Substantial Presence Test evaluates physical presence in the U.S. over a three-year period.

In some cases, individuals may hold dual status—being both a non-resident and resident alien for tax purposes within the same year. Such taxpayers must file a dual-status income tax return, adhering to specific IRS reporting requirements.

U.S. tax residents seeking benefits under foreign tax treaties should carefully review documentation requirements to substantiate their residency claims. Proper compliance ensures eligibility for treaty provisions while avoiding potential penalties.

A clear understanding of these regulations enables non-citizens to manage their U.S. tax obligations effectively and leverage available international tax agreements where applicable.