Substantial Presence Test

The Substantial Presence Test (SPT) is the primary statutory mechanism under IRC §7701(b) for determining US tax residency. It establishes whether a non-citizen is a US resident alien for federal income tax purposes. The test employs a weighted formula: a person is considered to have a substantial presence if they are physically present in the US for at least 31 days in the current calendar year AND meet a 183-day threshold calculated over a three-year period (current year weighted as 1.0× days, prior year as 0.33× days, and second-prior year as 0.167× days). For example, 100 days in the current year plus 100 days in each of two prior years yields approximately 183 weighted days. Crucially, the SPT contains several critical exceptions: the closer-connection exception allows individuals meeting the mathematical test to remain non-residents if they maintain a tax home outside the US and have a closer connection to another country than to the US. Additionally, tax treaties between the US and other nations (such as the US–Canada treaty) may provide tiebreaker rules to prevent dual residency. The IRS specifically exempts certain F-visa students, J-visa exchange visitors, and teachers under separate statutory provisions. The SPT also ignores days when individuals were unable to be present due to medical conditions. Determining resident alien status carries substantial consequences: resident aliens face worldwide taxation on all income, must file Form 1040, and lose certain foreign earned income exclusions. The authoritative IRS publication for navigating the SPT is Publication 519 (US Tax Guide for Aliens), which provides detailed calculation examples, exemption documentation requirements, and treaty considerations.