To claim someone as a dependent, they must either be a 'qualifying child' or a 'qualifying relative'
The five tests to claim someone as a qualifying child
1. Age test: Under 19 or
under 24 and full time student[/b] - she's got you there
2. Non-support test: You aren't providing one-half of your own support - from the way you described your situation, this test is not met
3. Relationship test: There's a list I won't type out, but as her child you meet this one
4. Principal residence: Must live with taxpayer more than half of the year (time spent away at school don't count as time 'away from principal residence') - since you don't ever live with her, she doesn't get this one either
5. Citizen or residency test: You must be a US citizen or a US, Canada, or Mexico resident - you didn't go into this, but I'll guess you meet this
You have to meet ALL five. So, I could've stopped after #2 but in case there are others reading who this might apply to I went through the rest of them.
However, if you fail the qualifying child test, there's a chance you can be claimed as a 'qualifying relative'
if these five (slightly different) tests are met:
1. Gross income test: The individual's income must be less than the dependency exemption amount (which goes up each year, it's $3,400 for 2007) - I'm guessing if you support yourself entirely you make more than this and she's already out of contention for QR. Again, I'll keep going in case someone else wants to know for themselves...
2. Support test: [Note: This is different than the support test above!] This time, the taxpayer must actually provide half of the potential dependent's support (as opposed to the dependent simply not providing half for themselves in the QC test...there, it doesn't matter who provides over half as long as it's not the dependent. Here, it must be the taxpayer wishing to claim them)
3. Relationship, or Member of Household test: Certain relatives (the IRS goes all genealogical on us - I won't do it here
) or non-relatives who've lived in the taxpayer's household for the entire year)
4. Citizen or Residency test - same as in QC
5. Joint return test - if you're married, you can't be filing a joint return with your spouse and still be claimed as a QR by someone else (unless you aren't required to filed b/c of your income and only did so to get a refund)
Finally, an individual can only be claimed by ONE person. So if someone is a QC of someone else, you can't take them as a QR. There's also different rules for children of divorced parents.
But in the OP's situation, from the facts you gave, your mom should NOT be claiming you. You have every right to claim yourself, it's not your fault she is filing improperly. Of course, if she has already claimed you and then you do so as well, there's a chance you'll both have to explain it. It won't just be her having to deal with it, unless she concedes - you'll also have to go through the hassle of proving why you deserve the exemption. So, if you still want to claim yourself, I'd talk to her and explain why she legally can't claim you and that she should refile. This way she'd at least avoid penalties & interest if/when she loses. She may decide she'd rather take her chances with not getting caught, but as a tax preparer I'm not allowed to advise "playing the audit lottery"