Hi,

For 2010 tax, my employer did not withhold FICA (SS/Medicare tax) as I was on OPT. I have filed Form 1040 and got my returns for 2010. Is it fine if I filed form 1040 instead of 1040 NR? Do I owe back taxes?

Edit: I entered US in 2006 on H1b. Since 2006-2008 was on H1B. 2008- on F1 (grad school). 2008 -2010 on F1. 2010 - OPT. Even when I was in school, I always filed Form 1040. Never used 1040 NR.

Your F-1 status dictates whether you are liable for FICA (Social Security and Medicare) taxes, NOT how you filed your federal income tax return.

It was legal for you to continue to file Form 1040 even though you changed your visa status, and, in my opinion, it was also legal for you to claim exempt status from FICA taxes based on your F-1 visa.