I never knew I could claim my son on my taxes and never have. Can I get the 18 years?

[melisa-cambpell]

Can I claim a child of 18 years if I was unaware I could?

[Mike9241]

years before 2020 are closed by the statute of limitations

assuming you are correct in that you can properly claim your son as a dependent (see below) you can file amended returns for 2020, 2021,2022

you did not reveal your filing status for those years 

if you properly filed as single you can now file as head of household or

if you were married in those years and used the filing status of married filing separately (MFS), then you may be able to change to head of household filing status [probably more beneficial than (MFS)] if you lived apart from your spouse for the last 6 months of each tax year and also for each tax year you paid more than 1/2 the cost of maintaining the household for you and your son, who if married did not file a joint return with his spouse, and who lived with you for at more than 6 months in each tax year.

to be able to claim your son as a dependent

1. you can not be eligible to be claimed as a dependent by someone else

2. your son must be a US citizen, US resident alien, US national or a resident of Canada or Mexico

you can claim him as a qualifying child if all these tests are met
• he has the same principal abode as you for more than ½ the tax year. Temporary absences like for school are ignored
• if he is not a full-time student, he's under 19 at the end of the tax year. If a full-time student, he's under 24 at the end of the tax year.
• he hasn't provided over ½ his own support
• he didn't file a joint return unless there was no tax liability but merely filing jointly to facilitate a refund of taxes withheld or estimates paid

or you can claim him as a qualifying relative if all these tests are met
• his gross income for 2022 less than $4,400 (less in 2022 and 2021)
• you provided over ½ his support
• he isn't a qualifying child of another taxpayer

support

• Includes amounts spent for food, lodging, clothing, education, medical and dental expenses, recreation, transportation and other necessities

[Opus 17]

To file an amended return with a claim for refund, you must file the amended return within 3 years of the original deadline, or within 2 years of the date you actually filed, if you filed after the deadline.  If you never filed at all, the claim for refund must be filed within 3 years of the original deadline.  For most taxpayers, that means that 2019 and earlier are closed for amending to get a refund, but an amended return could still be filed for 2020, 2021 or 2022.

Whether you will get a tax benefit is very complicated, depends on many factors, and you didn't give us any details.  If someone else claimed the child as a dependent, even if you were the person who was legally entitled, making a duplicate claim now will require the IRS to investigate you and the other taxpayer to determine who has the correct claim.  

We would need to know a lot more details.  What is your relationship to the child, when was the child born, where did they actually live (regardless of any custody agreement), who provided support, were there court/custody orders or agreements, did someone else claim them as a dependent, approximately how much income did you have and what kind (working or something else) and so on.