Hi, I am married and have a child and I was residing in Connecticut since Jan 2007 till Sep. 2011 on L1-Visa. Till now (2007,2008,2009,2010) I filed tax as full year resident. Now since I moved back to my country in Sep 2011, under what status I should file the tax (Part-year resident or Full year resident) for year 2011? Can I still file as full year resident?

You are Dual status. But according to Publication 519, your residency termination date is Dec 31, 2011, unless you qualify for earlier date. If you do not want to qualify, you are full year resident.
You should be able to file joint return as resident.

Filing as a resident is probably preferred (especially with a child due to the $1,000 Child Tax Credit), but you MUST claim all world-wide income. You can file Form 1116 to claim the Foreign Tax Credit for taxes paid to your home country's government on income earned since September 2011.

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Thanks MukatA,
I did not get what do you mean by "If you do not want to qualify, you are full resident"?

Thanks AtlantTaxExpert,
Is it must to claim (declare) the worlwide income as I would be paying tax on the income in my Home country, Also here we do file the tax after April, so do I need to file an extension first and then file the taxes in US once I file taxes in my home country?

You do NOT have to wait until you file your home country return if the country is India, since the withholding normally represents the actual tax.

We have received our W2 this year. My wife is on L1B and I am on L2 (not working), we have a son (2.5 years old) staying with us. We landed in US on Sept 2012.
While filing Tax returns, which forms we have to fill and do we need to apply for Tax ID number for my son also before filing Tax? I have my SSN.
Vish

Vish,

It is probably most advantageous for you to file jointly with your wife, filing Form 1040 with Form 1116 to claim the Foreign Tax Credit.  Form 1116 is required because you must claim ALL world-wide income earned in 2012, and the Form 1116 allows you to claim a credit for the income taxes paid to your home country. Note that you must WAIT until sometime in May before you can file this joint return.

You will need to apply for an Individual Tax Identification Number (ITIN) for your child by submitting Form W-7, and that process has undergone some radical procedural changes this past year.  Instead of the simple notarization process, the IRS now requires that your home country certify the photocopy of your passport as a true copy.  This is due to rampant fraud in the ITIN submission process.  The notaries simply cannot tell the difference between a fake passport and the genuine passport.

This certification can be done by the Indian (I assume you are from India) embassy in Washington, D.C. or at one of the consulates in San Francisco, Chicago, Houston or New York.  Assuming you do NOT want to drive there, you need to call the nearest consulate and arrange to have this process done via the mail.  Since you must wait until May to file, you have time to get this done (the process, done via mail, can take up to three months to complete). My clients to date have had the best results by mail with the San Francisco consulate, getting the certified passport photocopies in less than 3 weeks.

Also, the IRS recently announced the opening of Tax Assistance Centers through which you may be able to have the passport verifued as genuine, then submit the tax return and Form W-7 IN PERSON to be forwarded to the ITIN Processing Center in Austin, Texas for processing , without having to get the photocopies certified by your home country consulate. The list of the TACs are at the link below:

Taxpayer Assistance Center Locations Where In-Person Document Verification is Provided

The alternative is to mail in the actual passports themselves, something most of my clients are reluctant to do.

If you believe that you will need professional help filing this year, this IS what I do. Please double-click on my name (Atlanta Tax Expert) above to access my profile. You will find my email address in the signature portion of the profile (scroll down to the BOTTOM of the page).