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
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.
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