I was working in a company in F1 visa for 9 months under OPT and my H1b started from 1st October. That makes 9 months in F1 and 3 months in H1B visa. How do I calculate my taxes ?

Unless you are married, you will file as a non-resident, filing Forms 1040NR-EZ and 8843 one last time.

If you are married, you can file jointly with your spouse and you both CHOOSE to be treated as resident aliens. This will allow you to claim the $11,700 joint standard deduction plus two $3,750 personal exemption (for yourself and your spouse).

To apply for an ITIN, you need to complete Form W-7 for your spouse. You need to make a photocopy of his/her passport, then get the photocopy notarized. This can be done at your local bank in most states in the U.S.

This can also be done at a Indian notary, but if he/she will be coming to the U.S. within the next few months, you should get it done in the U.S. at any local bank, because, if done in India, he/she must also get a certificate of authenticity (called an apostille) from the Indian government. Depending on WHERE he/she lives, this can take from a few days to up to a YEAR.

The downside is that:

• You must wait until 1 June 2011 to meet the Substantial Presence Test before you can file for Tax Year 2010.

• You must declare ALL 2010 world-wide income (spouse's home country income, if applicable). There is an offset available by either claiming the Foreign Tax Credit (Form 1116) or to claim the Foreign Earned Income Exclusion (Form 2555).

Even with the downside, this is probably the best way for you to file.

I am sorry that I didn't add some imp info.

I am single and have been living in US for last 3 years. I have filled my return for 3 years as well as paid my taxes on income from my internships.

Okay, then file the Form 1040NR-EZ and Form 8843 one last time.

For 2011, you will file as a resident alien, probably filing Form 1040EZ.