This article is for information only and is not tax advice.
Calculus asks whether you stayed, or plan to stay, in the US for less than 31 days in total in 2026. Count all your visits to the US in 2026 together. Include the days you have already spent in the US and the days you plan to spend before December 31, 2026.
When do I answer Yes?
Answer Yes if you were, or will be, physically present in the US for less than 31 days in total during 2026. Answer No if your total is 31 days or more.
How do I count my days?
You count as present in the US on any day you are physically in the US at any time during that day. A part day counts as a full day. Add up the days of all your visits in 2026.
| Your 2026 visits | Total days | Your answer |
|---|---|---|
| One visit of 10 days in March and one visit of 12 days in September | 22 | Yes |
| One visit of 20 days in May and one visit of 15 days in October | 35 | No |
| One visit of 30 days | 30 | Yes |
| One visit of 31 days | 31 | No |
Why does the number 31 matter?
The IRS substantial presence test is one way to decide whether you are a US resident for tax purposes. To meet the test for a year, you must be physically present in the US for at least 31 days in that year. You must also meet a second requirement of at least 183 weighted days over three years.
If you are in the US for less than 31 days in 2026, you cannot meet the substantial presence test for 2026. Calculus uses your answer, together with your other residency answers, to decide whether you are a resident or a nonresident for tax purposes.
Do I count all the days I am in the US?
Count the days you are physically in the US. The IRS does not count some days toward the substantial presence test. These include:
Days you commute to work in the US from a residence in Canada or Mexico, if you commute regularly.
Days you are in the US for less than 24 hours while you travel between two places outside the US.
Days you work as a crew member on a foreign vessel.
Days you cannot leave the US because of a medical condition that started while you were in the US.
Days you are an exempt individual, for example certain students on F, J, M or Q status and certain teachers and trainees.
If you think one of these exclusions applies to you, contact the administrator who manages Calculus at your institution before you answer.
What if my plans change?
Calculus asks about your days in total for 2026, including days you plan to spend in the US. If your plans change, update your answer so that it matches your actual days. This matters if your total moves from fewer than 31 days to 31 days or more, or the reverse.
What are the key facts about the less than 31 days question?
| Question | Answer |
|---|---|
| What does the question ask? | Whether you stayed, or plan to stay, in the US for less than 31 days in total in 2026. |
| When do I answer Yes? | When your total days in the US in 2026 are 30 or fewer. |
| When do I answer No? | When your total days in the US in 2026 are 31 or more. |
| How do I count a day? | Any day you are physically in the US at any time during that day counts as one day. |
| Do I count all visits? | Yes. Add the days of all your visits in 2026, including days you plan to spend in the US. |
| Why does 31 days matter? | The substantial presence test requires at least 31 days of presence in the year. |
| Does the IRS exclude any days? | Yes. For example, days you are an exempt individual, days you are in transit for less than 24 hours, and some commuting days. |