@lgreenhill - There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, a relationship test and residence test. Only a QC qualifies a taxpayer for the Earned Income Credit.
Your 30 year old child can still be a QC if he has been diagnosed as disabled. Otherwise, he may qualify under the qualifying relative rules, which means you must be supporting him and he has very little income.
A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:
- He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
- He did not provide more than 1/2 his own support. Scholarships are considered third party support and not as support provided by the student.
- He lived with the parent (including temporary absences such as away at school) for more than half the year
A person can still be a Qualifying relative dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:
- Closely Related OR live with the taxpayer ALL year (not even one night at the non-custodial parent’s home).
- His/her gross taxable income for the year must be less than $4150 ($4,050 in 2017)
- The taxpayer must have provided more than 1/2 his support
In either case:
- He must be a US citizen or resident of the US, Canada or Mexico
- He must not file a joint return with his spouse or be claiming a dependent of his own
- He must not be the qualifying child of another taxpayer
if you filed for 2017 and 2018, without claiming him, you can file amended returns for those years to claim him now.
How to amend https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
