if they can legally claim you as a dependent in 2020 on your return you must check the box that you could be claimed as a dependent on someone else's return even if they don't claim you. those are the tax rules. if you try to claim yourself and they have already filed claiming you, your return will be rejected. if you file first, their return will be rejected if they claim you. they would need to mail in their return. eventually, if they and you claim you the IRS will send a notice to each asking for an amended return. if neither do, the IRS will send a second notice asking for proof. the taxpayers that provide the better support for being entitled to claim you will get to kept the dependent. the loser gets a bill for any additional taxes, interest and penalties.
they can claim you if
you are a qualifying child - all these tests are met
• you have the same principal abode as the other party for more than ½ the tax year. Temporary absences like for school are ignored
• If not a full-time student, under 19 at the end of the tax year. If a full-time student under 24 at end of tax year.
• you haven't provided over ½ your own support for 2020
• you didn't file a joint return unless there was no tax liability but merely filing jointly to facilitate refund of taxes withheld or estimates paid
or as you could be a qualifying relative if all these tests are met
• your related or if not lived with the other party for the entire year
• your gross income for 2020 is less than $4,300
• the other party provided over ½ your support
• you aren't a qualifying child of another taxpayer
