Source: http://www.familylawcenter.us/2016/06/09/what-is-the-law-on-child-support-for-adult-children/
Timestamp: 2019-04-19 16:51:55+00:00

Document:
A parent’s principle obligation is to financially support his or her minor children according to his or her circumstances and station in life. Fam. Code §4053(a). While this is a well-known fact, many parents fail to realize that they may be required to continue paying child support after their children reach the age of 18. There are three typical situations in which a parent’s duty to pay child support may continue after their children are no longer minors.
A very common situation in which child support may continue is when your child reaches the age of 18, but is still in high school and not self-supporting. In this circumstance, a court may require you to continue paying child support until your child reaches the age of 19 or graduates, whichever occurs first. Fam. Code §3901(a).
Another situation in which child support may continue even though your child is no longer a minor is when your child is unable to take care of himself or herself by working. The legislature has specifically stated, “a father and mother have an equal responsibility to maintain, to the extent of their ability, a child of whatever age who is incapacitated from earning a living and without sufficient means.” Fam. Code §3910(a).
The court will consider your child incapacitated if your child has an “inability to become self-supporting due to a physical or mental disability or upon proof of inability to work because of factors beyond your child’s control.” Jones v. Jones, 179 Cal.App.3d 1011, 1015 (1986). Courts have found an adult child to be incapacitated when an adult child had a maturity level of a twelve year-old (Chun v. Chun ,190 Cal.App.3d 589, 592 (1987)) and when an adult child suffered from chronic paranoid schizophrenia. In re Marriage of Drake, 53 Cal.App.4th 1139, 1154 (1997).
When a court determines whether your child has “sufficient means,” they look at the likelihood your child will become a public charge. In re Marriage of Drake, 53 Cal.App.4th 1139, 1154 (1997). Specifically, the court looks at whether or not your adult child will receive government benefits.
If you are ordered to pay adult child support it will be calculated the same way it is for minor children.
A court may also order child support for a child over the age of 18 based upon an agreement of you and the other parent. Fam. Code § 3587.

References: §4053
 §3901
 §3910
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 v. 
 § 3587