Twenty-one is the simple answer.
Of course, this being the law, there is more to the answer. Support can end before age 21 if the child is emancipated. Children are automatically emancipated when they are married or join the military. Just file a notice with the court unless there are children younger than the one being emancipated. More about that below.
Two scenarios exist where the child might be emancipated but not automatically. In one such scenario, the child is out of high school, not attending a post-secondary school and capable of supporting themselves. The second scenario requires the child to have removed himself/herself from the control and custody of either parent. Both scenarios require the non-custodial parent to file a petition with the court and prove that child should be emancipated.
What if there are younger children than one who should be emancipated?
The non-custodial parent must a petition to modify support for the remaining children. Here is another example of self-help being no help. One case where a father had three children and as each left home he modified his support by one-third without filing anything with the court. In the end, the court found the man in contempt and owing child support. Why? Because Indiana's child support guidelines do not operate on a simple mathematical basis but a more complicated algorithm. The Child Support Guidelines are here. I suspect he thought it was a brilliant idea to save legal fees.
If you need to check any possible changes in your child support, this is the online child support calculator from the Indiana Judicial Center.
One more thing: emancipation ends the obligation to pay current support but not any money owed for unpaid support. Here is the statute of limitations for enforcing child support obligations:
IC34-11-2-10I guess I get very surprised with this one. When my divorces are over, I try to make sure my clients know what rights and responsibilities they will have afterwards. I do not know why more attorneys do not do this. From conversations I have with clients wanting to enforce or modify their support, custody or visitation orders, I find no one tells them very much.
An action to enforce a child support obligation must be commenced not later than ten (10) years after:
(1) the eighteenth birthday of the child; or
(2) the emancipation of the child;
whichever occurs first.
As added by P.L.1-1998, SEC.6.