If a 23yo child lived with us the whole year I provided all support except for 1 month and we are filing jointly, can we claim her as a dependent if she's filed before?

Run the Interactive Tax Assistant

https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent

Your daughter may meet the dependency requirements as a qualifying relative.

 

TurboTax software will ask you simple questions and give you the tax deductions and credits for which you are eligible based upon your answers.

 

A dependent must meet the requirements of a qualifying child or a qualifying relative in order for you to claim them on your tax return.

 

The tests for a qualifying child are:

 

• Relationship: Must be your child, adopted child, foster child, brother or sister, or a descendant of one of these (grand or nephew).
• Residence: Must have the same residence for more than half the year.
• Age: Must be under age 19 or under 24 and a full-time student for at least 5 months. They can be any age if they are totally and permanently disabled.
• Support: The dependent must not have provided more than half of their own support during the year.
• Joint Support: The child cannot file a joint return for the year.

 

The tests for a qualifying relative are:

 

• Qualifying Child: They are not the “qualifying child” of another taxpayer or your “qualifying child.”
• Gross Income: The dependent being claimed earns less than $4,700 in 2023.
• Total Support: You provide more than half of the total support for the year.
• Member of Household or Relationship: The person (a friend, girlfriend, non-blood relative) must live with you all year as a member of your household or be related to you.

See also these TurboTax Helps here and here.

 

@cprue2018