IRS Substantial Presence Test (3-Year Weighted Formula) Calculator

How the 121-Day Annual Limit & Fractional Days Work

• The Exact IRS Formula: The IRS adds 100% of your days in the current calendar year + 1/3 of your days in the first preceding year + 1/6 of your days in the second preceding year. If the sum is 183.0 or higher (and current-year days >= 31), you pass the Substantial Presence Test.
• Fractional Days Are NOT Rounded Down: If 122 days each year gives 122 + 40.67 + 20.33 = 183.0 days, you trigger US tax residency! That is why 121 days/year (181.5 weighted days) is the universal safe ceiling for annual visitors.
• Commuters & Transit Exceptions: Regular commuters from Canada or Mexico who commute to work in the US on >75% of workdays, or travelers in continuous international airport transit (<24 hours between two foreign points), may exclude those specific days.
• Exempt Individuals (F-1, J-1, A, G Visas): International students (typically first 5 calendar years on F-1), teachers/trainees (J-1), and diplomats exclude their days by filing IRS Form 8843.

How Form 8840 (Closer Connection Exception) Saves Snowbirds & Nomads

• Who Qualifies for Form 8840: If your 3-year weighted total is 183 or more, you can STILL avoid US tax residency if (1) you spent fewer than 183 actual days in the US in the current year, (2) you maintained a "tax home" in a foreign country all year, and (3) you had a closer connection to that single foreign country than to the US.
• Why Digital Nomads Often Fail Form 8840: Form 8840 requires a closer connection to ONE specific foreign country where you maintain a permanent home, bank accounts, driver’s license, and tax registration. Perpetual travelers hopping across 8 countries with no fixed tax home may not qualify.
• Strict Filing Deadline: Form 8840 must be mailed to the IRS by June 15 of the following year (or April 15 if you also file Form 1040-NR). Missing the deadline can void the exception and trigger FBAR / FATCA penalties on foreign bank accounts.
• Immigration vs. Tax Rules: Even if a CBP officer stamps your B1/B2 visa for 6 months (180 days), CBP enforces immigration law while the IRS enforces tax law—staying the full 180 days for two years in a row triggers the IRS threshold.

If my ESTA allows 90 days per trip and I visit twice a year (180 days), am I a US tax resident?

Yes, unless you qualify for and file Form 8840 or a tax treaty tie-breaker. Spending 180 days in a single calendar year already puts you within 3 days of automatic residency, and if you spent even 9 days in the US the previous year (9 ÷ 3 = 3), your weighted total hits 183 days.

Does the IRS round down fractional days from the 1/3 and 1/6 calculation?

No. The IRS only excludes fractional days if the final sum of the 1/3 and 1/6 fractions leaves a fraction below 183 (for example, 182.67 days is under 183). When adding the 1/3 and 1/6 components together, you must keep the exact fractions before checking whether the total equals or exceeds 183.0.

What happens if I accidentally trigger the Substantial Presence Test without filing Form 8840?

If you become a US tax resident under the Substantial Presence Test, you are taxed on your worldwide income just like a US citizen or Green Card holder. Even worse, you become subject to FinCEN Form 114 (FBAR) on foreign bank accounts exceeding $10,000 and IRS information returns (Forms 5471, 8938, 3520) for foreign companies or trusts, which carry $10,000+ civil penalties per unfiled form.

Can a day spent flying through a US airport between Canada/Latin America and Europe be excluded?

Under the IRS international transit exception, if you are travelling between two foreign points and are physically present in the United States for less than 24 hours solely for the purpose of catching a connecting flight, that transit day does not count toward the Substantial Presence Test.