What is a non-resident alien?

For tax purposes, you're a non-resident alien if you're not a U.S. citizen or U.S. national and you don't pass either of the IRS's two residency tests. Passing either one makes you a resident alien instead.

You pass the green card test if you were a lawful permanent resident of the United States at any point during the tax year.

You pass the substantial presence test if you were physically present in the United States for both of the following:

• 31 days or more during the tax year, and
• 183 days or more across a three-year period, counting all of your days present in the tax year, one-third of your days present in the year before that, and one-sixth of your days present in the year before that.

Not every day of physical presence counts toward the test. The IRS excludes certain days, including some days for students, teachers, and trainees on specific visas. There are also exceptions that can leave you a non-resident alien even if your day count clears the test. See IRS Publication 519, U.S. Tax Guide for Aliens for the full rules.

If you don't pass the test this year but will next year

If you don't pass the substantial presence test for the tax year but expect to pass it the following year, you may be able to make the First-Year Choice and be treated as a resident for part of the tax year. Additional day-count conditions apply: Publication 519 covers them under First-Year Choice, in the Dual-Status Aliens section.

If you make this choice, you can't file your return for the tax year until you've passed the substantial presence test in the following year. You'll need to file an extension and wait until you meet the test before you file.