you mother can can claim you if these 5 test are met for qualifying child
1) related to you - YES
2) you're under 19 at end of year and younger than mother - YES
3) child must have the same principal residence as taxpayer for more than - YES
4) she provided over 1/2 your support - NO - YOU SAY YOU DID
5) didn't file a joint return, exception if filed joint return to get taxes paid in when there was no tax liability
- you didn't say if you are married to the father and if so did you or will you file a joint return
anyway because you say you provided over 1/2 your support, you do not meet the definition as a qualifying child so your mother can't claim you as such but there is a second possibility you could be a qualifying relative so let's check the tests for that
1) member of household - lived in her household all year except for temporary absences or be related - YES
2) gross income under $4,150 for 2018 - my guess if you worked and are filing a return you earned over this amount so NO
3) mother provided over 1/2 your support - again you say you did so answer is NO.
all tests are not met so you are not her qualifying relative
thus your mother is not supposed to claim you as a dependent because you are neither a qualify child nor qualifying relative (based on you claiming you provided over 1/2 your support) . if your mother filed and claimed you , you will not be able to e file. if she did filed and claimed you she needs to amend either now or later. if not now, each of you get a 1st notice from the IRS asking to amend by not claiming you as dependent. if nether responds, the IRS sends a second notice asking for proof. the one who submits the best proof wins the other gets a bill.
under the tax laws, the custodial parent gets to claim the child. this parent can allow the noncustodial to claim by giving that person a signed and completed form 8332 which they must submit with their return. without this form the IRS won't allow the non-custodial parent to claim the child - court order or personal agreement not withstanding.
you may want to use the following worksheet from the iRS to see if in fact you supported yourself.
https://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf
the same worksheet is in IRS publication 501 page 15
if the IRS asks and should you fail to prove you provided over 1/2 your support, you could face a sizable tax bill. if you are unsure of as to whether or not you meet the support test, seek out a professional to discuss your situation. l.
