What the IRS actually weighs. Whether someone is a bona fide resident is decided on the facts of the situation, and the IRS names intention or purpose for being in the country, activities there, and whether the person paid tax to that country among the relevant factors. The clearest qualifying pattern is someone who moves abroad for an indefinite or extended period and sets up permanent quarters for themselves and their family. The clearest failing pattern is the opposite: the IRS's own example is a person who goes abroad "to work for a specified period of time," who "ordinarily will not be regarded as a bona fide resident of that country even though you work there for one tax year or longer." A two-year contract with a defined end date and a return ticket is the hard case, and it is hard because the test is about settling, not about duration.
The entire-tax-year requirement is a hard edge, and it defeats people who were clearly living abroad. The uninterrupted period has to contain one complete tax year, so a calendar-year filer must be a bona fide resident from January 1 through December 31 of some year. Consider a person who arrives in Lisbon in November of one year and transfers back to the United States in December of the next. That is more than a year abroad and it fails, because no single tax year sits entirely inside the period. The physical presence test, whose 12-month window can start on any day, is the fallback in exactly that situation, and the IRS points to it by name.
Once the test is met, it reaches backward and forward into the partial years. After an uninterrupted period covering a full tax year is established, the person qualifies as a bona fide resident from the date residence began through the date it was abandoned. That means a full tax year plus parts of one or two other tax years can qualify, which is often where the most valuable part of the exclusion sits. The status is claimed in Part II of Form 2555, and the IRS cannot make the determination until that form is filed.
Brief trips do not break it; a change of intent does. During bona fide residence a person may leave the foreign country for brief or temporary trips, back to the United States or elsewhere, without losing the status, provided they clearly intend to return to the foreign residence or to a new foreign residence without unreasonable delay. What matters is the intent behind the travel, not its length in isolation. This is the practical advantage the test has over the day count, where the same travel simply subtracts days.
Two eligibility limits people miss. First, the statute grants the test to "a citizen of the United States." The IRS extends it to one further group: a US resident within the meaning of section 7701(b)(1)(A) who is a citizen or national of a country with which the United States has an income tax treaty in effect. A resident alien from a non-treaty country therefore has to use the physical presence test. Second, section 911(d)(5) contains a disqualifier that is easy to trigger by accident. If a person tells the foreign country's authorities that they are not a resident there, and those authorities hold them not subject to that country's resident income tax on the earnings as a result, the person is not a bona fide resident of that country for section 911 purposes. The IRS adds that while such a statement is pending and undecided, the person is likewise not treated as a bona fide resident. Claiming non-resident status abroad to reduce a foreign tax bill can therefore cost the US exclusion.
A foreign tax exemption by treaty does not by itself disqualify you. An income tax exemption provided in a treaty or other international agreement will not in itself prevent bona fide residence. Whether a particular treaty does is decided under all of its provisions, including any specific residence or privileges-and-immunities articles.