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If you are a resident alien, you must follow the same tax laws as U.S. citizens. You are taxed on income from all sources, both within and outside the United States and file the 1040 or 1040EZ
If you are a nonresident alien, you must file Form 1040NR or Form 1040NR-EZ if you are engaged in a trade or business in the United States, or have any other U.S. source income on which the tax was not fully paid by the amount withheld.
If you have a green card you are still considered resident alien.
I have a green card and understant I must return within one year after leaving the country.
You will file the 1040 form and if you meet the requirements to exclude your foreign earned income you can use the Form 2555 to exclude only earned income no unearned (pensions and interest)
How long can I keep doing this before I become a non resident in the eyes of US Internal revenue
You must give up your green card
at what point. I like to travel for extended periods - I'm retired
Lawful permanent resident aliens (green card holders) with no definite plans to return to the U.S. must notify the Department of Homeland Security of their termination of residency and file Form 8854, Initial and Annual Expatriation Information Statement, with the IRS if they:
Unless you take the steps to actively give up your green card you remain under tax for US as a resident alien
I hope this information has been helpful
Is a monetary difference in taxes due for a non resident or resident alien?
Resident aliens although taxed on worldwide income are afforded more deductions and credits. Nonresidents are not allowed all of these and the tax rate is generally 30%
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