Substantial Presence Test.
The formula deciding when time in the US makes you a US tax resident: this year's days, plus a third of last year's, plus a sixth of the year before. Reach 183 — with at least 31 days in the current year — and the IRS taxes your worldwide income.
Figures on this page are stated for tax year 2025/26 UK · 2025 US. Thresholds change annually.
Days accumulate faster than you think
About 122 days a year, sustained, crosses the line. Arrival and departure days each count in full, which catches frequent business visitors and snowbirds who never intended residence — but a layover of under 24 hours between two places outside the US does not count at all. The closer-connection exception and the treaty tie-breaker can rescue the position, and both require forms, not just facts.
- Weighted three-year day count; 183 is the trigger
- Students, diplomats and some visa classes exempt
- Form 8840 or 8833 needed to claim the way out
The formula, worked through
You count every day in the current year, one third of the days in the previous year and one sixth of the days in the year before that. If the total reaches 183, and you spent at least 31 days in the United States this year, you meet the test.
So three years of 120 days each gives 120 plus 40 plus 20, which is 180, just under the line. A few extra days in any of the three years can tip it over.
| Days this year | Last year | Year before | Weighted total | Result |
|---|---|---|---|---|
| 120 | 120 | 120 | 180 | Below the test |
| 130 | 120 | 120 | 190 | Meets the test |
| 30 | 300 | 300 | Not counted | Under 31 days this year, so not met |
The ways out of it
Some people's days are not counted at all, including certain students, teachers, trainees and diplomats. Others meet the test but can escape it through the closer connection exception, which needs fewer than 183 days in the current year, a tax home abroad and a closer connection to that country, claimed on Form 8840.
Where someone is resident in both countries, the treaty tie-breaker may assign residence to one of them. Claiming it is a treaty position disclosed on Form 8833, and it has consequences beyond the income tax return.
Questions we get about this
Generally yes: a day of arrival or departure counts as a full day. The main exception is transit: fewer than 24 hours in the United States while travelling between two places outside it does not count as a day of presence.
No. It is a weighted three-year count: all of this year's days, a third of last year's and a sixth of the year before. You also need at least 31 days in the current year. People often pass it with far fewer than 183 days in any single year.
Yes, under each country's domestic rules at the same time. The treaty tie-breaker can then decide residence for treaty purposes, working through permanent home, centre of vital interests and other tests. Claiming it is disclosed on Form 8833.
It lets someone who meets the test be treated as a nonresident if they were in the United States fewer than 183 days in the current year, kept a tax home abroad and had a closer connection there. It is claimed on Form 8840, filed on time.
Related pages
- Glossary
Saving Clause: definition
The treaty provision that lets the US tax its citizens as if the treaty didn't exist.
- Service
183-day US residence status
The US 183-day rule explained: the substantial presence test formula, exempt individuals, the closer connection exception and the treaty tie-breaker.
- Free tool
Substantial Presence Test
Count your US days under the substantial presence formula, apply the weighting and exemptions, and see whether you are a US tax resident for the year.
- Pillar guide
Tax specialists for US and UK
What US and UK tax specialists handle that a general accountant does not: residence tests, treaty relief, FBAR, PFICs, pensions, property and catch-up filings.
- Who we help
Brits in the US
UK citizens in the US: residency tests, UK property and pensions held from abroad, and the reporting that US residence triggers on everything left behind.
- Service
1040-NR tax returns
Form 1040-NR preparation: US-source income for nonresident aliens, effectively connected income, 30% withholding, treaty claims and dual-status years.
Further reading
- The statutory residence test in the year you move
Arrival and departure years are where the test bites hardest, and where Americans get it wrong most often. Here is how the three stages actually run.
- Do you need to file a US tax return from abroad?
Owing nothing is not the same as not filing. The duty follows citizenship, the thresholds are lower than people assume, and some forms apply regardless of income.
Last reviewed · Figures stated for tax year 2025/26 UK · 2025 US. Thresholds and rates change annually — check figures against the current tax year before relying on them.
Want this handled properly?
Describe your situation and we will tell you what is actually required, with a fixed fee to handle it.