Can I file a FAFSA even if I haven't filed taxes yet?
Yes. For example, if you want to file a 2012-2013 FAFSA as soon as possible for the 2012-2013 academic year, you can do so on January 1, 2012. It will require information from your 2011 taxes. But understandably, you probably won't file your 2011 taxes until getting your W-2 from your employer at the end of January 2012.
The solution is to simply estimate your 2011 tax information on your 2012-2013 FAFSA. Then, after you have filed your 2011 taxes, you can correct your 2012-2013 FAFSA information, if necessary.
To correct FAFSA information that was previously filed, first wait to receive your SAR (Student Aid Report), which indicates that your initial filing has been processed. This typically happens within 2 weeks of providing the Department of Education with your signature. Then go to https://fafsa.ed.gov/FAFSA/app/fafsa and enter the student's first name, last name, Social Security Number, and date of birth. Then click on Make FAFSA Corrections. You will then need to enter a Federal Student Aid PIN number. If you don't already have a PIN, you can get one by going to http://www.pin.ed.gov.