更新于 2026年10月26日

Two Different 183 Day Tests: Section 937 and the Substantial Presence Test

Two tests share the number 183 and little else. The substantial presence test weights three years for aliens in the U.S. Section 937 counts actual days in Puerto Rico.

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Are the substantial presence test and the Puerto Rico presence test the same thing?

No. They share the number 183 and almost nothing else. The substantial presence test decides whether a foreign national is a U.S. resident for tax purposes, and it uses a weighted count over three years. The section 937 presence test is one of three tests for being a bona fide resident of Puerto Rico, and its main alternative is a plain count of at least 183 days actually spent on the island in the tax year.

Search for one and you often get pages about the other. That is how readers end up applying a weighted formula to a Puerto Rico day count, or the reverse. The sections below pull them apart.

What question does each test answer?

The substantial presence test is the Internal Revenue Code's day-count test for deciding whether an alien is treated as a U.S. resident. It asks about days in the United States.

The section 937 presence test is the day-count part of the bona fide resident definition. Section 937(a) asks about days in a possession, and Puerto Rico is one of the five possessions it names. Presence is only the first requirement. The statute also requires that you have no tax home outside the possession and no closer connection to the United States or a foreign country than to the possession.

How does the substantial presence test count days?

The substantial presence test is met when you are physically present in the United States at least 31 days in the current year and at least 183 days over a three year period. The IRS page on the substantial presence test gives the weighting:

All of your days in the current year.
One third of your days in the first prior year.
One sixth of your days in the second prior year.

The IRS example uses 120 days in each of 2023, 2024, and 2025. For 2025 that is 120 plus 40 plus 20, which is 180. That is below 183, so the test is not met for that year.

The same page says that for this test the United States does not include U.S. territories. A day in Puerto Rico is therefore not a day in the United States for the substantial presence test.

What does section 937 count?

The section 937 test is not weighted. The statute requires physical presence in the possession for at least 183 days during the taxable year, with days counted under the principles of section 7701(b). Our guide to the 183-day rule for Puerto Rico covers the headline count in detail.

26 CFR section 1.937-1(c) adds alternatives for a U.S. citizen or resident alien. You meet the presence test if you satisfy any one of them:

At least 183 days in the possession during the tax year.
At least 549 days over the current year and the two preceding years, with at least 60 days in each of those three years.
No more than 90 days in the United States, on the terms the regulation and Publication 570 set out.
U.S. earned income of $3,000 or less and more days in the possession than in the United States.
No significant connection to the United States.

The 549 day alternative looks like a three year test, and that is where the confusion peaks. It is an unweighted count. Every day in each of the three years counts as one day, and the 60 day minimum applies to each year. The substantial presence formula counts a prior year day as one third or one sixth of a day.

Passing the presence test does not make you a bona fide resident. The tax home test and the closer connection test must also be met in the same year, as Publication 570 explains.

Do both tests use a closer connection idea?

Yes, and the two ideas are related but not identical.

Under the substantial presence rules, the closer connection exception can keep a person who meets the day count from being treated as a U.S. resident. 26 CFR section 301.7701(b)-2 requires three things: fewer than 183 days of presence in the United States in the current year, a tax home in a foreign country, and a closer connection to a single foreign country where the tax home is maintained than to the United States. It is unavailable to someone who has applied, or taken other affirmative steps, to become a lawful permanent resident.

Section 937 borrows from that regulation. Section 1.937-1(e) says the principles of section 301.7701(b)-2(d) apply to the closer connection test for a possession, without regard to the final sentence of section 301.7701(b)-2(b). The factors come from the same list: where your permanent home, family, and personal belongings are, where you bank, vote, and hold a driver's license, and which country you name on official forms.

The comparison runs differently. For a possession, your ties to Puerto Rico are weighed against your combined ties to the United States and to foreign countries, and the question is whether you had a closer connection elsewhere at any part of the year. The substantial presence exception compares the United States against one foreign country. For the full framework, see the presence, tax home, and closer connection tests.

Why do the two tests get mixed up?

Three things cause the mix-up.

First, the number. Both tests contain 183, but one is a weighted total over three years and the other is a count of real days in a single year.

Second, the shared lineage. Section 937(a) says days in a possession are counted under the principles of section 7701(b), the same section that houses the substantial presence test. That cross-reference governs how a day is counted, not which formula is used.

Third, a rule in Publication 570. A nonresident alien does not use the five presence conditions that apply to citizens and resident aliens. Publication 570 says a nonresident alien applies the substantial presence test from Publication 519, with the territory substituted for the United States. So the weighted formula does show up in a Puerto Rico setting, but only for that group.

	Substantial presence test	Section 937 presence test
Question	Is an alien a U.S. resident for tax?	Is the person a bona fide resident of the possession?
Place counted	The United States, excluding territories	The possession, such as Puerto Rico
Day math	31 days current year, and 183 weighted days over three years	At least 183 days in the year, or another listed alternative
Three year rule	Weighted by 1, one third, and one sixth	549 days with at least 60 in each year, unweighted
Closer connection	Exception, single foreign country, fewer than 183 days	Third test, possession ties against all U.S. and foreign ties

Which column applies to you depends on your status, so Puerto Rico is not a foreign country for these rules is worth reading if you are working from foreign-country language in the regulations.

What should you take from this?

Pick the test that matches your question. Then count days in the place that test names. For bona fide residency in Puerto Rico, count actual days on the island and check which of the listed alternatives you meet. Then confirm the tax home and closer connection tests separately.

Keeping that count by hand is the part many people abandon. One83 builds a day-by-day record from your calendar so the count exists before anyone asks for it. Whether a specific year turns on one test or the other is a question for your advisor, who can apply the rules to your facts.

Frequently Asked Questions

Does the weighted three year formula apply to the Puerto Rico presence test?

Not for a U.S. citizen or resident alien. Section 937 asks for at least 183 days of actual presence in Puerto Rico, or one of the other alternatives in 26 CFR 1.937-1(c). Publication 570 says nonresident aliens use the substantial presence test with the territory substituted for the United States.