The 183-day test: how visitors become US taxpayers by arithmetic.
US tax residence can arrive without a visa changing: spend enough days in the country and the substantial presence test makes you a US taxpayer on worldwide income. The formula is stricter than the '183 days this year' most people assume.
Figures relate to tax year 2025 (US) · 2025-26 (UK)
The formula counts three years
You meet the test with at least 31 days in the current year and 183 weighted days across three: all of this year's days, plus one-third of last year's, plus one-sixth of the year before. A steady 122 days a year — a quarter of the year, every year — crosses the line.
Some days don't count: certain students, teachers and diplomats are exempt individuals, and days you couldn't leave due to a medical condition that arose in the US are excluded. Commuting and transit rules carve out more.
- Current days + ⅓ prior year + ⅙ the year before
- 31-day minimum in the current year
- Exempt-individual and medical-day exclusions
- ~120 days a year, sustained, triggers the test
Two escape routes, claimed in time
Cross the threshold and two defences remain. The closer-connection exception — under 183 actual days this year, a tax home abroad, and a demonstrably closer connection to it — is claimed on Form 8840. Miss its conditions and the US–UK treaty tie-breaker can still assign residence to the UK, claimed on Form 8833 with a 1040-NR.
Both are filings with deadlines, not facts that assert themselves. For UK residents with heavy US travel, we track the day count before the year ends — while the remedy is still a calendar change rather than a return.
Primary sources
Official guidance from the IRS, FinCEN and GOV.UK. Thresholds and rates on those pages are updated annually — check the current tax year before relying on a figure.
Questions, Answered.
What clients ask about 183-day us tax residence
I stayed under 183 days this year. Am I safe?
Not necessarily — the test is weighted across three years, so repeated substantial visits accumulate. Under the formula, about 120 days a year sustained is enough. The single-year 183 figure only matters for the closer-connection exception.
What's the difference between Form 8840 and the treaty tie-breaker?
Form 8840 claims the closer-connection exception — available only under 183 actual days in the current year. The treaty tie-breaker on Form 8833 works even past that, weighing home, personal and economic ties, but brings more filing obligations with it. We use the lightest tool that fits the facts.
Do partial days in the US count?
Generally yes — any part of a day present counts as a day, with narrow exceptions for transit under 24 hours and regular commuters. Arrival and departure days are the ones travel diaries most often miscount.
Does the substantial presence test apply to Green Card holders?
No — Green Card holders are US tax residents automatically, regardless of days. The day-count test matters for everyone else: visitors, business travellers and those on nonimmigrant visas.
How do I prove my days of presence in the US?
Passport stamps, airline records and the I-94 travel history the US publishes online are the backbone; calendars and receipts fill gaps. We reconcile the official I-94 record against your own diary before relying on either.
Next Step.
Tell us what you hold — the scope and a fixed fee follow in writing.