What are the criteria for a non-resident alien to file taxes in the United States?

A non-resident alien generally must file a U.S. tax return if they were engaged in a trade or business in the United States during the tax year, or if they have U.S. source income for which tax was not fully withheld at the source. Even if no tax is due, a return may be required in certain situations, such as when claiming a refund or treaty benefits.

Key criteria include:

1. Engaged in a Trade or Business in the U.S.: If a non-resident alien conducts any trade or business within the U.S., they are typically required to file a tax return (Form 1040-NR) to report their U.S. effectively connected income (ECI).
2. U.S. Source Income Not Fully Withheld: If a non-resident alien has U.S. source income (such as wages, interest, dividends, royalties) and the tax was not fully withheld by the payer, they may need to file a return to report this income and pay any remaining tax. This often applies to Fixed, Determinable, Annual, or Periodical (FDAP) income.
3. Claiming Refunds or Treaty Benefits: A non-resident alien may need to file a tax return to claim a refund of overpaid taxes or to benefit from tax treaty provisions that reduce or eliminate U.S. tax on certain types of income.
4. Exempt Individual Status: Certain individuals, such as students or trainees on F, J, M, or Q visas, are exempt from the Substantial Presence Test. However, they may still need to file Form 8843 if they were present in the U.S. for any part of the year, even if they have no U.S. income.

It is important to note that the definition of "engaged in a trade or business" and what constitutes "U.S. source income" can be complex and may depend on specific circumstances and tax treaty provisions.