The US Substantial Presence Test: 183 days, weighted
14 July 2026 · 5 min read
In short
You are a US tax resident under the Substantial Presence Test if you spend at least 31 days in the US in the current year AND your weighted total — all of this year's days, plus one-third of last year's, plus one-sixth of the year before — reaches 183. That means as few as 122 days a year, every year, makes you a US tax resident.
Not a simple 183-day rule
Most countries count days within one year. The US Substantial Presence Test is different: it adds a weighted look-back. You are a US tax resident for a calendar year if you are present at least 31 days in that year and the following sum reaches 183:
- all of your US days in the current year, plus
- one-third of your US days in the previous year, plus
- one-sixth of your US days in the year before that.
The famous consequence: about 122 days per year, three years running, is enough (122 + 40.7 + 20.3 ≈ 183). Frequent visitors who "never stay six months" can still become US tax residents.
Which days count
Any part of a day physically present in the US generally counts as a full day — stricter than the UK's midnight rule. There are narrow exceptions for days in transit, commuters from Canada or Mexico, crew members, certain students and teachers on exempt visas, and days you could not leave because of a medical condition.
The closer-connection escape hatch
If you cross the weighted 183 but stayed under 183 actual days in the current year, you may avoid US residency by showing a tax home in, and closer connection to, another country — filed on Form 8840. That claim stands or falls on your day counts, so the log matters either way.
How TaxDin helps
Because TaxDin keeps a complete multi-year history of your location, the three-year weighted arithmetic is straightforward to check — and the same log serves your UK, India, Singapore and UAE counts. US tax is famously unforgiving; use a qualified adviser for anything borderline.