This is my first entry in U.S and I came on July 4th 2011 and I am married. My wife got EAD but currently not working. Which form I need to submit (resident or non resident), how much percentage will I get my tax refund. My stay is less than 183 days. Which form I can submit to get maximum tax refund..

If you wait until early May 2012 (to meet the Substantial Presence Test), you can and should file jointly with your wife.

You will need to claim ALL world-wide income for 2011, but you can offset any added tax by claiming the Foreign Tax Credit (Form 1116), which is filed with Form 1040.

You will also submit Form W-7 to get your wife an Individual Tax Identification Number (ITIN).

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Due date is April 2012, if I wait till May will there be penalty for me? My wife has SSN.
Which form I need to submit (resident or non resident), how much percentage will I get my tax refund. My stay is less than 183 days. Which form I can submit to get maximum tax refund..

You are filing as a resident when you file Form 1040. The way I suggested WILL get you the maximum refund.

As for exceeding the 15 April 2012 deadline, file Form 4868 to get an extension to 15 October 2012. Problem solved!

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That means if I file as Non resident I will not be getting much tax refund in compare to resident tax refund am I correct ? What about using Form 8840 so that its not required to pay taxes? Again am I correct?

You are mis-informed about the use of Form 8840. It will NOT exempt you from federal income tax; it only extends your non-resident alien status if you meet certain criteria.

For most international students, filing as a resident results in less tax.

What about if I maintain my Tax Home in my country, in that case do I need to pay taxes here ? What will the tax rate applied for 1040 NR, is it 30 %?

I am referring Tax Home in the following article > Tax Home section.

http://www.investopedia.com/articles/tax/11/tax-tips-for-non-residents.asp#axzz1lpEjPdaU

Then you will file as a non-resident alien, and STILL pay income taxes to the United States. It is basic principle in EVERY tax treaty that each country gets to tax income that is generated within that country's borders.

As for FICA taxes, that is a matter of U.S. tax law that dictates that FICA taxes get paid after five years on F-1 status has passed.

What will the tax rate applied for 1040 NR, is it 30 % flat any deductions allowed for my Spouse ?

The same tax rates that the residents pay applies to your non-resident return. If you file as a non-resident, then you CANNOT claim your wife.

That is why I am pushing the JOINT return, because the taxes WILL be lower.