Days You Could Not Leave
The substantial presence test under IRC §7701(b)(3) counts physical days in the United States. A separate set of provisions, mostly gathered in IRC §7701(b)(7), removes specific days from that count before the calculation runs, for reasons that have nothing to do with visa category or exempt-individual status. A medical emergency, a short layover, a daily commute across the border, and a stint on a foreign ship each has its own rule, its own conditions, and, in one case, its own annual filing requirement.
Five reasons a day might not count
The exempt individual exclusion, covered in a separate dossier, removes days for people in specific visa categories, such as students and teachers, subject to year limits that track the visa. The provisions here are different: they exclude particular days for anyone, regardless of visa status, based on the circumstances of that specific day.
| Exception | Governing provision | What it covers |
|---|---|---|
| Medical condition | IRC §7701(b)(7)(E), Treas. Reg. §301.7701(b)-3(c) | Days an individual was unable to leave because of a medical condition that arose while present |
| Regular commuter | IRC §7701(b)(7)(B), Treas. Reg. §301.7701(b)-3(e) | Days spent commuting to U.S. employment from a residence in Canada or Mexico |
| Transit between foreign points | IRC §7701(b)(7)(C), Treas. Reg. §301.7701(b)-3(d) | Days present less than 24 hours while traveling between two points outside the United States |
| Crew member | IRC §7701(b)(7)(D) | Days present as a regular crew member of a foreign vessel engaged in transportation to or from the United States |
The medical condition exception, and its critical limit
IRC §7701(b)(7)(E) excludes a day from the count if the individual intended to leave the United States on that day but was unable to because of a medical condition that arose while the individual was present. The exclusion is aimed at people who fell ill or were injured during a visit and could not travel, not at people who traveled to the United States because they were already sick.
Treas. Reg. §301.7701(b)-3(c) draws that line explicitly. If the individual is aware of a preexisting medical condition before arriving in the United States, and enters the country intending to obtain treatment for that condition, the days spent in the United States receiving that treatment are not excluded, because the condition did not arise while the individual was present, it existed before arrival and was the reason for the trip. The exception is for the traveler whose business meeting, vacation, or visit was interrupted by an unexpected medical event, not for medical tourism, however genuine the underlying condition and treatment may be.
This is a factual question that depends heavily on medical documentation. A claim for the exclusion is supported by a statement from the treating physician confirming both the nature of the condition and, specifically, that it prevented departure on the days claimed. A condition that made travel merely inadvisable is treated differently from one that made it impossible, and the regulation is written around genuine inability to leave rather than a preference to stay for care.
The commuter exception from Canada and Mexico
IRC §7701(b)(7)(B) excludes days spent performing services in the United States by an individual who regularly commutes to U.S. employment or self-employment from a residence in Canada or Mexico. This exception exists because a person living just across either border and working in the United States daily is not, in any functional sense, residing in the United States, and Congress did not intend the substantial presence test to reach that fact pattern the way it reaches genuine relocation.
The regulations attach a specific regularity threshold to the word "regularly." Treas. Reg. §301.7701(b)-3(e) looks to whether the individual commutes to United States employment or self-employment on more than 75 percent of the workdays during the working period involved. A person who works in the United States most days but travels back to a Canadian or Mexican residence only occasionally, rather than as the individual's genuine daily pattern, is less likely to satisfy that threshold and should not assume the exception applies without checking the actual commuting pattern against it.
The transit exception, and how narrow it actually is
IRC §7701(b)(7)(C) excludes a day on which the individual is physically present in the United States for less than 24 hours while traveling between two points outside the United States. This covers the traveler changing planes at a U.S. airport on the way from one foreign country to another, where the layover itself is brief and incidental to the journey.
The exception is narrower than the 24-hour figure alone suggests, because the regulations require that the time in the United States be genuinely in transit. An individual who leaves the airport to attend a business meeting, conduct a site visit, or otherwise engage in activity not directly related to traveling through the United States breaks the exception for that day, even if the total time on the ground stays under 24 hours. The exception is built for the layover, not for a same-day business trip structured to stay under the clock.
Crew members of foreign vessels
IRC §7701(b)(7)(D) excludes days on which an individual is present as a regular member of the crew of a foreign vessel engaged in transportation between the United States and a foreign country or a U.S. possession. The exclusion is tied to the crew role itself: a day on which the same individual otherwise engages in any trade or business in the United states, separate from the crew member's duties aboard the vessel, is not excluded, regardless of the person's status as crew for the rest of that voyage. A crew member who also works a shoreside job during a port call has stepped outside the exception for that day.
Which of these require an annual statement, and which do not
Only one of the four provisions here carries a mandatory annual filing requirement of its own. Treas. Reg. §301.7701(b)-8 requires an individual claiming the medical condition exception to file Form 8843, Statement for Exempt Individuals and Individuals with a Medical Condition, completing Part V, by the due date, including extensions, of whatever return the individual would otherwise be required to file. Without that statement, the exclusion is not respected even where the underlying medical facts would otherwise support it.
| Exception | Form 8843 required |
|---|---|
| Medical condition | Yes, Part V, filed by the applicable due date |
| Regular commuter | No separate statement, though records supporting the commuting pattern should be retained |
| Transit between foreign points | No separate statement, though travel records supporting the under-24-hour, in-transit nature of the stay should be retained |
| Crew member | No separate statement, though crew and voyage records should be retained |
The commuter, transit, and crew exceptions are applied directly in the day count without a corresponding filing, but that does not mean they are unquestioned. If the IRS challenges the day count on a return, the burden of substantiating that a specific day genuinely fell within one of these categories, through commuting records, travel itineraries, or vessel and crew documentation, sits with the taxpayer.
A worked example of the medical condition line
Consider a visitor who arrives in the United States on a routine business trip, planning to stay two weeks, and suffers a serious accident during week one that requires hospitalization and makes flying impossible for a further six weeks. Once the physician confirms the individual was medically unable to travel, the days beyond the original planned departure, for as long as the inability to travel continues and is documented, are excluded from the substantial presence count under IRC §7701(b)(7)(E), provided Form 8843 is filed with the required physician's statement.
Change the facts: the same visitor already knew, before booking the trip, that a scheduled surgery would take place during the visit, and traveled to the United States specifically to have that surgery performed by a U.S. specialist. Even though the medical need is entirely genuine and the individual is, in a plain sense, also unable to leave during recovery, Treas. Reg. §301.7701(b)-3(c) treats this differently, because the condition did not arise while the individual was present, it existed beforehand and motivated the trip. Those days count toward the substantial presence test in the ordinary way. The distinction turns entirely on timing and intent at the moment of arrival, not on the severity or genuineness of the medical need itself, which is why documentation addressing when the condition arose, not only what the condition was, is central to supporting the claim.
Why the commuter and transit exceptions get less scrutiny in practice, and why that is not protection
Because the commuter, transit, and crew exceptions do not require a filed statement, they tend to draw less routine attention than the medical condition exception, which is flagged by the presence of Form 8843 itself. That difference in visibility is not a difference in legal footing. An examiner reviewing a borderline substantial presence position can, and does, request records supporting any day excluded under these provisions, and the absence of a pre-filed statement means the taxpayer is reconstructing the support after the fact rather than having already put it on record. A commuter relying on the more-than-75-percent threshold should keep a contemporaneous log of actual crossings, not reconstruct one from memory years later when the day count is questioned. A traveler relying on the transit exception should retain boarding passes and itineraries showing the connection times and confirming no activity occurred outside the airport or transit corridor. A crew member should retain the vessel's voyage and crew manifests for the relevant days.
How this fits with the broader substantial presence count
Each of these exceptions operates day by day rather than as a status that applies to an entire year, which distinguishes them from the exempt individual category covered elsewhere. A person can be a regular commuter for most of a year, then take a job that requires actually living in the United States for a stretch, and only the genuine commuting days are excluded; the rest are counted normally. The same is true of a medical condition that resolves partway through a stay: only the days of genuine inability to leave are excluded, and ordinary presence resumes being counted once the individual is able to travel again. Getting the substantial presence total right requires applying these day-level exceptions to the underlying day count described in the substantial presence dossier on this site, not treating either set of rules as a substitute for the other.
Next steps
Anyone relying on the medical condition exception should secure a physician's statement addressing inability to leave, not merely the existence of a condition, and file Form 8843 by the applicable due date. Anyone relying on the commuter, transit, or crew exceptions should keep the underlying travel, employment, or vessel records that would support the claim if the day count is later questioned, since none of those three exceptions come with a filed statement that establishes the position on its own.
This is general information about how these day-exclusion rules operate as of the date written. It is not advice on any individual's day count, and applying these exceptions to a specific travel history belongs with a qualified preparer.