While the Physical Presence Test (PPT) is what US expats use to exclude income, the Substantial Presence Test (SPT) is the IRS rule that determines if a non-citizen (or a US citizen who isn’t sure of their status) is considered a US tax resident.
The SPT applies to non-residents, Green Card holders, and US citizens who spend significant time in the country. If you meet the SPT, you are taxed on your worldwide income, just like any US resident. For frequent visitors, international entrepreneurs, and those returning to the US for extended periods, this is the most critical calculation.
How the Substantial Presence Test Works
The SPT is based on a weighted, three-year average of your physical presence in the US. You meet the SPT if you are present in the US for:
- 31 days during the current year, AND
- 183 days during the three-year period, counting:
- 100% of the days present in the current year.
- 1/3 of the days present in the immediate preceding year.
- 1/6 of the days present in the second preceding year.
A common mistake is thinking you only need to look at the current year. Because of the weighted average, even a short trip this year could trigger US tax residency if you spent a lot of time in the US in the previous two years.
Case Study: How 60 Days Can Ruin Your Year
Imagine you spent 120 days in the US in 2023 and 120 days in 2024. In 2025, you think, “I’ll keep my time under 60 days this year.”
| Year | Days Present | Weighting | Weighted Total |
|---|---|---|---|
| 2025 | 60 days | x 1 | 60 |
| 2024 | 120 days | x 1/3 | 40 |
| 2023 | 120 days | x 1/6 | 20 |
| 3-Year Total: | 300 days | 120 days |
Wait, if your weighted total is 120 days, how did you meet the 183-day threshold? Because the 183-day rule is a sum of the weighted days.
Ah, the calculation above is actually how the 183-day threshold is met, which is often the confusion. In this scenario, your total weighted days is 120. You would not meet the 183-day weighted test, but you did meet the 31-day minimum for the current year.
Let’s look at a true SPT trigger scenario:
| Year | Days Present | Weighting | Weighted Total |
|---|---|---|---|
| Current (2025) | 100 days | x 1 | 100 |
| Preceding (2024) | 100 days | x 1/3 | 33.33 |
| Second Preceding (2023) | 300 days | x 1/6 | 50 |
| 3-Year Total: | 500 days | 183.33 days |
In this case, spending only 100 days in the US in 2025 (which is over the 31-day minimum) means you meet the 183-day weighted average, making you a US tax resident for 2025, subject to worldwide income taxation.
The complexity of the weighted calculation and the rolling 3-year lookback requires precision—especially if you travel frequently.
Don’t risk a massive tax bill because of a weighted-average miscalculation.
Whether you are a non-resident concerned about accidentally triggering US tax residency, or a US citizen worried about the PPT, the underlying issue is the same: the calculation is too complex for manual tracking. Our ResidencyCheck Validation Test calculates your exact Substantial Presence Test (SPT) status across three years instantly, giving you a definitive, auditable answer.
Get the clarity you need. Secure your tax status with the $499 ResidencyCheck Compliance Agent.