When do you have to start filing federal income tax?

For tax year 2009 tax return that you will file in the year of 2010.

Generally a person who is self-employed must file a tax return if their net earnings from self employment for the year exceed $400, and pay social security and Medicare taxes and any income taxes that may be due.

If a dependent on some one else tax return and unearned income (pension, rent, interest, dividends, capital gains, etc.) over 950 must file a tax return.

For more detailed information on filing requirements go to www.irs.gov and use the search box for 1040 choose 1040 instruction and go to page 7 thru 9.

http://www.irs.gov/pub/irs-pdf/i1040.pdf

And of course you do not want to forget the state as they could have different filing requirements and possibly some benefits you could be entitled to if you were to file a tax return with them