How Does Child Support Work in Illinois?

How to Change Child Support When a Child Turns 18 in Illinois

Video by Attorney Kevin O'Flaherty
Article written by Illinois & Iowa Attorney Kevin O'Flaherty
Updated on
October 28, 2019

In this article, we explain how to change child support obligations when a child turns 18 in Illinois.  We will explain how child support works in Illinois.  We will answer the question, “Do I have to go to court to change my child support when my child turns 18 or graduates high school?”  We will answer a reader question, “If I modify my child support order to remove payments for a child that turns 18, will the court modify payments for my other children?; if so, will the new Illinois child support guidelines be applied?”  

For an overview of Illinois child support law, check out our article: Illinois Child Support 2019.

How Does Child Support Work in Illinois?

Child support laws changed significantly on July 1, 2017.  Child support orders entered prior to July 1, 2017 were calculated based on a flat percentage of the obligor’s income.  The flat percentage increased based on the number of children covered by the order.  

Child support orders entered after July 1, 2017 take into account the income of the recipient.  Under both the old guidelines and the new guidelines, the amount of child support is increased based on the number of children involved. To learn more about the change Illinois Child Support Laws, check out our article: Changes to Illinois Child Support Laws.

Child support typically terminates when a child reaches the age of 18 or graduates from high school.  (To learn about child support for post-high school education, check out: Illinois Child Support and College Expenses).  If there are multiple children covered by the child support order, child support should be reduced as each child reaches adulthood.


Do I Have to Go to Court to Change My Child Support When My Child Turns 18 or Graduates High School?

How does child support change when your child turns 18?

When a significant life event happens, such as one of the parties losing his or her job or one of the children reaching adulthood, one of the parents may have grounds to seek modification of the required child support payments. However, the parents cannot modify child support obligations on their own by simply starting to pay less in child support when a child reaches adulthood, even if the change is by mutual agreement.  

Rather, in order to change child support obligations, the parent seeking to change the obligation must file a motion to modify child support with the court that has jurisdiction over the child support order.  Motions to modify child support require that the movant show a “substantial change in circumstances” that would warrant a modification of the order.  A child turning 18 or graduating high school would certainly qualify as a substantial change in circumstances that would be grounds for reduction or termination of child support.  

Whether the obligor actually has to go to court to change the child support obligation depends on the language of the child support order.  Child support orders will often provide for automatic termination or reduction based on these events.  The date that a child will reach the age of 18 is easy to calculate.  The order may provide that child support automatically terminates on this date.  

If the language of your child support order does not provide for automatic termination or reduction, then the obligor will have to file a motion to modify child support with the court in order to terminate or reduce child support when a child reaches 18 or graduates from high school.

To learn more about how to modify a child support order, check out our article, Illinois Child Support Modification Explained.


If I Modify My Child Support Order to Remove a Child Turning 18, Will My Child Support Obligation for Other Children Be Modified?

Do I have to modify my child support?

As discussed above, child support orders entered prior to July 1, 2017 follow the old Illinois child support guidelines and orders entered after that date follow the new guidelines.  Interestingly, orders that were entered prior to July 1, 2017 under the old law that are now modified will apply the new guidelines when modifying the order.  However, the change in the law alone does not qualify as a “substantial change in circumstances” and does not in and of itself allow for modification of child support orders to apply the new guidelines.  

The upshot is that for parents who stand to benefit under the new child support laws a substantial change in circumstances other than the mere passage of the law is required in order to have the new law applied to your pre-2017 child support order.

Bringing the conversation back to the subject at hand, if a child support order covers multiple children and if the language of the order does not provide that child support is not automatically reduced when one child reaches the age of 18, the obligor will have to file a motion to modify child support to reduce his or her child support payments in light of the fact that one of the children has reached adulthood.  When this motion to modify child support is heard, the court will likely recalculate the remaining child support obligation pertaining to the other children based on the new guidelines, even if the original order was based on the old guidelines.

This is a general rule that may depend on the language in the order and any prior agreement of the parties that gave rise to the original order.  However, generally child support orders direct that a lump sum payment be made on a monthly basis.  Although this lump sum is calculated based on the number of children involved, the order will typically not provide that a particular portion of the child support obligation is allocated for each child.  This is why, the entire child support obligation will typically recalculated according to the new guidelines when one child reaches adulthood if the order does not provide for this scenario in advance.  


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Do I Have to Go to Court to Change My Child Support When My Child Turns 18 or Graduates High School?

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