Income is not a deciding factor. How old? Are they a full time student? Who can you claim,
https://ttlc.intuit.com/community/credits-and-deductions/help/who-can-i-claim-as-my-dependent/00/26781
If the dependent is your qualified child who is under 19 or a full-time college student under the age of 24, it does not matter how much they made.
For many other dependents the amount is $4200---not counting Social Security.
Those are over-simplifications. Here are some rules:
WHO CAN I CLAIM AS A DEPENDENT?
You can claim a child, relative, friend, fiance (etc.) as a dependent on your 2019 taxes as long as they meet the following requirements:
Qualifying child
• They are related to you.
• They cannot be claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They are not filing a joint return with their spouse.
• They are under the age of 19 (or 24 for full-time students).
• They live with you for more than half the year (exceptions apply).
Qualifying relative
• They don't have to be related to you (despite the name).
• They cannot be claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They are not filing a joint return with their spouse.
• They lived with you the entire year.
• They made less than $4200 (not counting Social Security)
• You provided more than half of their financial support. More info
When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them.
Related Information:
• Does a dependent have to live with me?
• What does "financially support another person" mean?
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent