Cross-Border Tax Guide: How to File a U.S. Tax Return as an International Taxpayer
Tax year 2025 (filed in 2026)
Pioneer Professional Accountants Inc. | Cross-Border Canada-US Tax
Updated: January 20, 2026
International tax filing in the U.S. starts with one key question: are you a U.S. tax resident for the year, or a nonresident? Your answer drives which return you file, what income you report, and whether treaty disclosures apply.
Step 1 - Determine your U.S. tax residency
- Resident alien (Form 1040): generally if you meet the green card test or the substantial presence test.
- Nonresident alien (Form 1040-NR): generally if you do not meet those tests.
- Dual-status: part-year resident/part-year nonresident, which often requires special formatting.
Note on Form 8843 (students/teachers/trainees and certain others)
Form 8843 is used to claim excluded days of presence for the substantial presence test (exempt individuals and certain medical condition claims). If you qualify to exclude days as an exempt individual (for example, some students or scholars), you generally must file Form 8843 with your return, or as a stand-alone filing if you are not required to file an income tax return.
Step 2 - Make sure you have a U.S. taxpayer ID
- If you are eligible for a Social Security Number (SSN), you should use it for tax filing.
- If you are not eligible for an SSN, you may need an ITIN (often requested using Form W-7, typically submitted with a tax return unless an exception applies).
Step 3 - Identify what income must be reported
If you are a nonresident (Form 1040-NR)
- Effectively Connected Income (ECI): generally U.S. trade/business income taxed at graduated rates (often includes U.S. employment income).
- FDAP income: certain U.S.-source passive income often subject to withholding at 30% unless reduced by treaty.
If you are a U.S. tax resident (Form 1040)
- U.S. residents generally report worldwide income (U.S. and non-U.S.).
- Foreign tax credits (Form 1116) and other cross-border relief may be available, depending on facts.
Step 4 - Treaties and treaty disclosures (Form 8833)
The U.S. has tax treaties with many countries (including Canada). Treaty benefits may reduce withholding or change how an item is taxed. If you claim a treaty position that overrides or modifies the Internal Revenue Code, you may need to attach Form 8833. The IRS also lists common exceptions where Form 8833 is not required.
Step 5 - File on time (key deadlines for 2025)
- Form 1040 (most U.S. residents): generally due April 15, 2026 for calendar-year filers.
- Form 1040-NR: generally due April 15, 2026 if you received wages subject to withholding; otherwise generally June 15, 2026.
- Extensions may be available, but any tax owing is generally due by the original due date to avoid interest.
Common additional filings
- FBAR (FinCEN Form 114): separate electronic filing for certain foreign accounts.
- Form 8938 (FATCA): specified foreign financial assets reporting for certain U.S. taxpayers.
- State returns: may apply depending on where you lived/worked and the source of income.
How we help
- Residency analysis (including day counts and exempt individual rules).
- Treaty review and disclosure support (Form 8833 when required).
- Preparation of U.S. federal + state returns, and coordination with Canadian T1 filings for cross-border clients.
- Cross-border compliance guidance (FBAR/FATCA) and documentation checklists.
Important note
This document is general information only. International tax rules are fact-specific and can change. Before acting on any treaty or residency position, obtain professional advice.
References
- IRS Publication 17 (Nonresident alien filing deadlines for 2025 returns).
- IRS Instructions for Form 1040-NR (Due dates and filing guidance).
- IRS: Claiming tax treaty benefits (Form 8833 rules and exceptions).
- IRS: About Form 8843 / Exempt individual guidance.
