U.S.-abroad tax field guide
The treaty is one layer. Your last U.S. state is another.
Start with the official treaty, map the U.S. federal overlays, then document the facts your former state uses for domicile and residency. This hub turns that three-layer review into a usable plan.
Destination law
First determine whether the destination treats you as tax resident and how it classifies each income stream.
Treaty + U.S. federal
Use the exact treaty, protocol, saving clause, and U.S. domestic rules—never a one-line 'tax treaty' claim.
Your U.S. state
Review domicile, abode, day-count, and retained ties under the state’s own law and instructions.
Initial destination set
Five routes already central to TotallyNomad planning tools
Portugal, Mexico, Spain, Thailand, and Costa Rica are the five destinations named in the existing country-comparison workflow. Four have U.S. income-tax treaties; Costa Rica is included because planning without a comprehensive treaty is a materially different case.
Portugal
The U.S.–Portugal income-tax treaty can allocate taxing rights and provide relief in defined situations, but it does not switch off ordinary U.S. filing for U.S. citizens.
Open field guideSpain
The U.S.–Spain treaty and protocol address categories of cross-border income, residence conflicts, and relief, while the saving clause preserves broad U.S. taxing rights over citizens.
Open field guideMexico
The U.S.–Mexico treaty coordinates defined income-tax issues between two neighboring systems, but U.S. citizens normally remain inside the U.S. worldwide-income filing system.
Open field guideThailand
The U.S.–Thailand income-tax treaty covers defined residence and income issues; its application depends on the exact article, domestic rules, and the treaty’s saving clause.
Open field guideCosta Rica
Costa Rica does not appear in the IRS A-to-Z list of U.S. income-tax treaties. That makes domestic law, income sourcing, and available U.S. relief mechanisms especially important.
Open field guideFive guardrails before you use a treaty
- A tax treaty does not automatically make foreign income tax-free.
- U.S. citizens generally remain subject to U.S. tax filing on worldwide income while abroad.
- The treaty saving clause often preserves U.S. taxing rights, with limited exceptions that depend on the treaty.
- Federal treaty treatment does not settle state domicile or statutory residency.
- FEIE and the foreign tax credit are domestic-law provisions with separate qualification rules.
Interactive organizer
Build a move-specific review list
Choose a destination, note your former state and retained ties, then use the result to organize records and adviser questions. It does not score eligibility or calculate tax.
Your planning checklist
Portugal: treaty + state-residency review
In force. The U.S.–Portugal income-tax treaty can allocate taxing rights and provide relief in defined situations, but it does not switch off ordinary U.S. filing for U.S. citizens.
This tool stores nothing and does not determine residence, treaty eligibility, or tax owed. It is an educational organizer for a conversation with qualified U.S. and destination-country advisers.
Primary sources
Official sources accessed October 1, 2026. Always re-check the current text and filing-year instructions.
Current IRS index for treaty texts and related technical explanations.
IRS Publication 54 — Tax Guide for U.S. Citizens and Resident Aliens Abroad ↗Federal filing, foreign earned income, housing, and residency overview for Americans abroad.
IRS — Foreign Tax Credit ↗Official overview of the credit that may reduce double taxation of foreign-source income.
IRS — Foreign Earned Income Exclusion ↗Official eligibility and filing overview; moving abroad alone does not qualify someone.
California FTB Publication 1031 — Guidelines for Determining Resident Status ↗Official California guidance on residency, domicile, temporary or transitory purpose, and safe-harbor concepts.
New York Department of Taxation — Definitions used to determine resident status ↗Official New York definitions for domicile and statutory residency.
Virginia Tax — Residency Status ↗Official Virginia explanation of domiciliary, actual, part-year, and nonresident status.
Educational only. This guide is not tax, legal, financial, or accounting advice. Tax residence, domicile, treaty eligibility, source rules, filing obligations, and available relief depend on specific facts and current law. Use qualified advisers in both jurisdictions.