Claiming a dependent child this year for last year

Failure to claim your child on your 2021 tax return does not preclude you from claiming him on your 2022 tax return (which you will prepare in first part of 2023).  If child is under 24 and a full-time student during 2022, you can claim him on your 2022 tax return as a dependent.

Hi Mike! Thank you for this excellent question - the rules for claiming a dependent are:

1. The child must be your son, daughter, stepchild, foster child, brother, sister, half brother, half sister, stepbrother, stepsister, or a descendant of any of them.

2. The child must be (a) under age 19 at the end of the year and younger than you (or your spouse if filing jointly), (b) under age 24 at the end of the year, a student, and younger than you (or your spouse if filing jointly), or (c) any age if permanently and totally disabled.

3. The child must have lived with you for more than half of the year.²

4. The child must not have provided more than half of his or her own support for the year.

5. The child must not be filing a joint return for the year (unless that joint return is filed only to claim a refund of withheld income tax or estimated tax paid).

So if they meet the requirements above you can claim them as a dependent. 

Here are some resources to help: 
https://turbotax.intuit.com/tax-tips/family/rules-for-claiming-a-dependent-on-your-tax-return/L8LODbx94
https://www.irs.gov/publications/p501#en_US_2021_publink1000196863