What is the substantial presence test?

It is the IRS day-count formula that determines US tax residency for non-citizens without a green card. You meet it if you are present in the US at least 31 days in the current year and 183 days over a three-year period, counting all days this year, one-third of last year's days, and one-sixth of the days from two years ago. Meet it and you are a resident alien (worldwide taxation); fail it and you remain a nonresident alien.

What US income is a nonresident alien taxed on?

Only US-source income, in two categories. FDAP income — fixed or determinable annual or periodical income such as US dividends, interest, rents and royalties — is generally taxed at a flat 30% withholding rate unless a tax treaty reduces it. ECI — income effectively connected with a US trade or business — is taxed at the same graduated rates that apply to US residents, after deductions. Foreign-source income of a nonresident alien is generally outside US tax.

Does a non-resident who owns a US LLC pay US tax?

Often not, but it depends on the income. A nonresident alien who owns a single-member US LLC and earns no income effectively connected to a US trade or business generally owes no US federal income tax — but the LLC must still file Form 5472 with a pro-forma 1120 each year, with a $25,000 penalty for failure. If the business has US-effectively-connected income (US employees, US inventory, services performed in the US), that income becomes taxable.

Which tax form does a nonresident alien file?

Form 1040-NR, the US nonresident alien income tax return, is used to report US-source income. Nonresident aliens generally cannot use the standard deduction (with limited treaty exceptions), cannot file jointly in most cases, and may need an ITIN (Individual Taxpayer Identification Number) if they are not eligible for a Social Security number. Many also interact with Form W-8BEN, which they give to US payers to certify foreign status and claim treaty benefits.

What Is a Nonresident Alien? US Tax Status Explained (2026)

Q: What is a nonresident alien?

A nonresident alien is a person who is not a US citizen and does not meet either of the two tests for being a US resident for tax purposes: the green-card test (holding lawful permanent residence) or the substantial-presence test (a day-count formula based on time spent in the US). If you are not a citizen and fail both tests, the IRS treats you as a nonresident alien, and the US can generally only tax your US-source income — not your worldwide income.

Q: How is a nonresident alien different from a resident alien?

The difference is what the US can tax. A resident alien (green-card holder or someone who passes the substantial-presence test) is taxed like a US citizen — on worldwide income — and files Form 1040. A nonresident alien is taxed only on US-source income, files Form 1040-NR, and is subject to special rules: flat 30% withholding on certain passive US income (unless a treaty lowers it) and graduated rates on income effectively connected with a US business.

"Nonresident alien" is an IRS term, not an immigration one, and it controls how much US tax a non-American actually owes. Get the status right and a non-US founder can run a US business paying little or no US income tax; get it wrong and you either overpay or face penalties. This guide explains who counts as a nonresident alien, the two residency tests, what income the US can reach, and why the status sits at the centre of the non-resident-founder playbook. Written primarily for non-US persons.

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Doola — US company formation, EIN and the Form 5472 filings nonresident owners must not miss.

The definition

A nonresident alien is anyone who is (1) not a US citizen and (2) not a US resident for tax purposes. You are a US resident for tax — a resident alien — if you meet either of two tests:

The green-card test: you hold lawful permanent residence (a green card).
The substantial-presence test: you spend enough time in the US under the IRS day-count formula.

Fail both, and you are a nonresident alien. The label is about tax, set by the IRS rules on residency, and it is independent of your visa status.

The stakes are large: a resident alien is taxed on worldwide income like a citizen; a nonresident alien is taxed only on US-source income. For a founder living abroad, that difference is the whole game.

Resident alien taxed on worldwide income versus nonresident alien taxed only on US-source income — Resident = worldwide income. Nonresident = **US-source only**.

The substantial-presence test

This is the test most non-citizens need to watch, because spending too much time in the US can flip you to resident status. You meet it if both are true:

You were present in the US at least 31 days in the current year, and
You were present 183 days over a three-year window, counting:
all days this year, plus
one-third of last year's days, plus
one-sixth of the days from two years ago.

If the weighted count reaches 183, you become a resident alien and the US taxes your worldwide income. Frequent US visitors — founders doing US roadshows, snowbirds — should track days carefully. Certain people (students, diplomats, some teachers) get exempt-day treatment, and a "closer connection" exception or a treaty tie-breaker can sometimes preserve nonresident status.

Substantial presence test: 31 days this year and 183 weighted days over three years — Cross the weighted **183-day** line and you become a resident for tax.

What the US can tax: FDAP vs ECI

A nonresident alien's US-source income falls into two buckets, taxed very differently:

FDAP income — fixed or determinable annual or periodical income: US dividends, interest, rents, royalties. Generally taxed at a flat 30% withholding at source, unless a tax treaty reduces the rate. No deductions.
ECI — income effectively connected with a US trade or business. Taxed at the normal graduated rates after deductions, on a net basis, via Form 1040-NR.

Foreign-source income of a nonresident alien is generally outside US tax altogether. This is the structural reason a non-resident can sell software or services to US customers from abroad and owe no US income tax — that income is typically foreign-source, not ECI.

Why it matters for founders

This status is the foundation of the non-resident US-business playbook:

A nonresident alien who owns a single-member US LLC with no US-effectively-connected income generally pays no US federal income tax — but the LLC must file Form 5472 annually ($25,000 penalty if missed) and needs an EIN.
If the business develops ECI — US employees, a US office, inventory in a US warehouse, services performed while physically in the US — that income becomes US-taxable.
A nonresident building a startup to raise US capital may instead need a US C-corporation, which changes the tax picture entirely.

Nonresident-owned US LLC with no ECI pays no US income tax but must file Form 5472 — No US-connected income, no US income tax — but **Form 5472** is mandatory.

Non-resident setting up in the US?

Firstbase.io handles formation, EIN and compliance for founders outside the US.

Forms and numbers you will meet

Form 1040-NR — the nonresident alien income tax return.
Form W-8BEN — given to US payers to certify foreign status and claim treaty rates (lowers that 30% FDAP withholding).
ITIN — an Individual Taxpayer Identification Number, for those not eligible for a Social Security number.

Common mistakes

Confusing immigration status with tax status. "Nonresident alien" is a tax classification; your visa does not decide it — the two residency tests do.

Triggering the substantial-presence test by accident. Too many US days flips you to worldwide taxation.

Owning a US LLC and ignoring Form 5472. No tax due does not mean no filing due — the penalty is $25,000.

Not filing W-8BEN. Without it, US payers withhold the full 30% on FDAP income even when a treaty would reduce it.

When to consult a qualified professional

Get advice if you spend significant time in the US, earn US-source income, own or plan to own a US entity, or are unsure whether your income is ECI. A cross-border CPA can confirm your status, file Form 1040-NR and 5472 correctly, and apply any treaty benefits.

Soveraine is an editorial publication, not a tax firm. Read our editorial policy and disclaimer before acting on anything in this article.