Tax Residency Determination: Tests, Exceptions, and Impact

U.S. tax residency determination runs on two tests: whether you hold a green card at any point during the year, and whether you spend enough time on U.S. soil to meet the substantial presence formula. Satisfy either one and the IRS treats you as a resident for the whole year, which means reporting your worldwide income rather than only what you earn from U.S. sources. Miss the rules and the penalties start at $10,000 for a single unfiled form.

The Green Card Test

If you hold a green card at any point during the calendar year, you are a U.S. tax resident for that entire year. Where you actually lived, how many days you spent in the country, and whether you earned anything from a U.S. source are all irrelevant.¹ Someone who spent eleven months abroad still owes tax on worldwide income if their lawful permanent resident status was never formally given up.

That status stays in effect for tax purposes until it has been officially revoked or a court or immigration agency has determined it was abandoned.¹ There is a trap worth knowing about: if you use a tax treaty to claim residency in another country and stop filing as a U.S. resident, the IRS treats that as a surrender of your green card for tax purposes, which pulls you into the expatriation rules covered at the end of this article.

The Substantial Presence Test

Without a green card, you can still become a U.S. tax resident by spending enough time in the country. The formula uses a rolling three-year window. You meet the test if you were present in the United States for at least 31 days in the current year and your weighted day total across three years reaches 183 or more.¹

The weighting: each day in the current year counts in full, each day in the prior year counts as one-third, and each day two years back counts as one-sixth.¹ Spending 120 days a year for three straight years gives you 120 + 40 + 20 = 180 days, just under the line. Add a few more days in any year and you cross it.

A “day of presence” is any calendar day when you were physically in the United States at any point. A morning meeting in Manhattan and an evening flight out still counts as a full day. The one carve-out is transit: if you pass through the U.S. between two foreign destinations and your presence lasts less than 24 hours, that day is ignored.¹

Once you meet the test, your residency starting date is generally the first day you were present in the U.S. that year.² If you also hold a green card, the earlier of your first day of presence or your first day as a lawful permanent resident controls.

Exceptions That Override the Day Count

Meeting the formula does not automatically lock you into residency. Three exceptions can pull you back out, but each requires specific documentation filed on time.

Closer Connection to a Foreign Country

If your weighted days hit 183 but you were physically present in the U.S. for fewer than 183 days in the current year, you may qualify for the closer connection exception. You must have kept a tax home in a foreign country for the entire year and show that your personal and economic ties there are stronger than your ties to the United States.³

The IRS looks at where your permanent home is, where your family lives, where you keep personal belongings, where you vote and hold a driver’s license, where you make charitable contributions, and where your social, cultural, and religious affiliations lie.³ No single factor decides the question; the picture as a whole does.

One hard disqualifier: you cannot claim the exception if you have applied for a green card or taken any step toward lawful permanent resident status during the year. Filing an I-485 (adjustment of status) or I-140 (immigrant worker petition) ends eligibility.³ You claim the exception on Form 8840, and missing the deadline forces you to show clear and convincing evidence of reasonable efforts to comply.

Exempt Individuals

Some visa holders are removed from the day count entirely. Their U.S. days simply do not register. Foreign government personnel with diplomatic status fall into this group.¹

Students on F-1 visas are exempt for five calendar years, so the substantial presence clock does not begin until that period ends.⁴ The five-year count uses full calendar years. Arriving in August burns the whole year as one of the five. The exemption depends on staying in compliance with visa terms and not switching to a non-exempt status.

Medical Condition

If you intended to leave the United States but could not because a medical condition arose while you were here, those extra days can be excluded. The exception is narrow. You cannot use it if you came to the U.S. specifically for medical treatment, or if you knew about the condition before arriving.⁵ You also lose it if you were eventually able to leave and stayed beyond a reasonable time to arrange your departure.

You claim the exception on Form 8843, with a physician’s statement confirming the condition. Miss the filing and the days count against you.⁵

What Changes When You Are Classified as a Resident

The resident-versus-nonresident line changes far more than which income is taxable. It reshapes your filing obligations, reporting requirements, payroll taxes, and deductions.

Worldwide Versus U.S.-Source Income

A U.S. tax resident owes tax on income from every source in the world. Wages from a foreign employer, interest from an overseas bank account, rental income from property abroad, capital gains from selling international assets — all of it goes on Form 1040. Nonresidents are taxed only on U.S.-source income, such as wages for work performed in the United States or rent from U.S. property.⁶

For nonresidents, U.S.-source income not connected to a U.S. trade or business generally faces a flat 30% rate, withheld when paid. Tax treaties can lower that rate. Interest on ordinary bank deposits is exempt from the 30% tax for nonresidents.⁶

Foreign Account Reporting

Residents with foreign financial assets face two separate reporting regimes that people constantly confuse.

FATCA requires Form 8938 if the total value of your specified foreign financial assets exceeds $50,000 on the last day of the tax year, or $75,000 at any point during the year (for unmarried taxpayers living in the U.S.).⁷ Failure to file triggers a $10,000 penalty, with up to $50,000 more if you still do not file after IRS notice. Undisclosed assets can also draw a 40% penalty on any related understatement of tax.⁸

The FBAR is separate. Filed on FinCEN Form 114, it applies whenever the combined value of your foreign financial accounts exceeds $10,000 at any time during the year.⁹ Non-willful violations reach $10,000 per violation. Willful violations run to the greater of $100,000 or 50% of the account balance. The FBAR is filed electronically through FinCEN, not with your tax return, which is a common reason people miss it.

Social Security and Medicare

Residency status also drives payroll tax exposure. Nonresident aliens on certain visas are exempt from Social Security and Medicare tax on U.S. wages. F-1 students, J-1 researchers and teachers, and employees of foreign governments and international organizations working in an official capacity all qualify.¹⁰ The exemption lasts only while the worker keeps nonresident alien status and performs work consistent with the visa. Once you become a tax resident, standard withholding applies.

Totalization agreements between the United States and several partner countries can also change the picture. A worker temporarily assigned to the U.S. from a treaty partner may keep contributing to the home country’s system instead, avoiding double contributions.¹⁰

Standard Deduction

Nonresidents cannot claim the standard deduction.¹¹ A narrow exception exists for students and business apprentices from India under the U.S.-India treaty. Everyone else filing as a nonresident must itemize or take nothing.

Arrival and Departure Years

The year you arrive in or leave the United States often produces a dual-status return. You are a nonresident for one part of the year and a resident for the other, and both periods appear on the same filing.

During the resident portion, worldwide income is taxable. During the nonresident portion, only U.S.-source income is. Your status on December 31 decides which form leads. Residents at year-end file Form 1040 marked “Dual-Status Return” with a Form 1040-NR attached as a statement for the nonresident period. Nonresidents at year-end reverse it: Form 1040-NR leads, with a Form 1040 statement covering the resident months.¹²

Dual-status filers lose the standard deduction and cannot file as head of household. Joint returns are generally unavailable unless a spouse is a U.S. citizen or resident and both elect joint filing. Income not connected to a U.S. business during the nonresident period is still taxed at the flat 30% rate or a lower treaty rate.¹²

When Two Countries Both Claim You

Dual residency happens when the U.S. and another country each treat you as a resident under their own laws. A green card holder who also meets residency criteria back home is a common example. Without a resolution mechanism, both countries would tax you fully.

Most modern U.S. tax treaties resolve this through a sequence of tiebreaker rules drawn from the OECD Model Tax Convention. The tests run in order and stop at the first one that produces a clear answer: where your permanent home is available, where your center of vital interests lies (family, business, social ties), where you have a habitual abode, and then nationality. If none of those settles it, the tax authorities of the two countries negotiate a resolution between themselves.

Most cases resolve at the permanent home or center of vital interests stage. An IRS memo on treaty residency shows the factors that get weighed at the center of vital interests level, including the location of a taxpayer’s family, place of business, and even their professional advisors.¹³ Not every U.S. treaty follows the model exactly, so the specific treaty between the two countries controls.

Leaving the U.S. Tax System

Giving up U.S. citizenship or surrendering a green card after holding it long enough can trigger an exit tax. It applies to “covered expatriates,” a status defined by three independent thresholds; hitting any one is enough.

You are a covered expatriate if your net worth is $2 million or more on the expatriation date, or if your average annual net income tax liability for the five preceding years exceeds an inflation-adjusted amount ($206,000 for 2025).¹⁴ The third trigger is failing to certify on Form 8854 that you complied with all federal tax obligations for the five preceding years.

Green card holders are subject to these rules only as “long-term residents,” meaning they held lawful permanent resident status in at least 8 of the 15 tax years ending with the year of expatriation. Surrendering a green card after six years, for instance, keeps you outside the exit tax regime.

The tax runs on a mark-to-market basis: your worldwide assets are treated as sold at fair market value on the day before you expatriate. Gain is taxable, but an exclusion shields a large slice ($890,000 for 2025, adjusted annually for inflation). Gain above the exclusion is taxed at normal capital gains rates.¹⁴ Form 8854 is filed with your income tax return for the year including the expatriation date, and failure to file carries a $10,000 penalty per year unless you can show reasonable cause.¹⁵

1
Office of the Law Revision Counsel. 26 USC 7701 – Definitions
2
Internal Revenue Service. Residency Starting and Ending Dates
3
Internal Revenue Service. Closer Connection Exception to the Substantial Presence Test
4
Internal Revenue Service. Tax Residency Status Examples
5
Internal Revenue Service. Form 8843 – Statement for Exempt Individuals and Individuals With a Medical Condition
6
Office of the Law Revision Counsel. 26 USC 871 – Tax on Nonresident Alien Individuals
7
Internal Revenue Service. Instructions for Form 8938
8
Internal Revenue Service. Summary of FATCA Reporting for US Taxpayers
9
Internal Revenue Service. Report of Foreign Bank and Financial Accounts (FBAR)
10
Internal Revenue Service. Aliens Employed in the US – Social Security Taxes
11
Internal Revenue Service. Nonresident – Figuring Your Tax
12
Internal Revenue Service. Taxation of Dual-Status Individuals
13
Internal Revenue Service. Assistance Concerning the Residency of a Foreign National
14
Internal Revenue Service. Expatriation Tax
15
Internal Revenue Service. Instructions for Form 8854