Child Support in Illinois

Overview

To calculate potential child support payments in Illinois, you must follow a three-step analysis:

1. Is a person oblgated to pay child support? Child Support is intended to ensure the child is properly taken care of given the resources of their parents. Both parents are legally required to support their child. The parent that does not have majority parenting time (calculated based on the number of overnights) typically must pay child support.

2. How much are the Child Support payments? Illinois provides a detailed procedure for calculating Child Support payments. See 750 ILCS 5/505(a)(1) This involves calculating the total income of both parents, using a formula to determine how much total the typical family with this income would spend on a child (the "Basic Support Obligation"), and then calculating each parent's share. The Illinois Department of Healthcare and Family Services provides a Calculation Worksheet that helps to explain the calculations.

3. How long will Child Support payments be required? Illinois requires the Obligor (the person paying Child Support) to make payments until the child turns 18 or graduates high school (if this is after they turn 18) or 19:

The termination date shall be no earlier than the date on which the child covered by the order will attain the age of 18. However, if the child will not graduate from high school until after attaining the age of 18, then the termination date shall be no earlier than the earlier of the date on which the child's high school graduation will occur or the date on which the child will attain the age of 19. See 750 ILCS 5/505(g).

Who Must Pay Child Support in Illinois?

As a general rule, the non-custodial parent must pay child support in Illinois. The Illinois Department of Healthcare and Family Services provides an Illinois Child Support Estimator on their website that can be used to calcualte Child Support payments. The amount of Child Support payments depends in part on the number of overnights the child spends with each parent. If both parents have at least 146 overnights, this is considered "Shared Physical Care," and the obligor is generally required to pay significantly less money in Child Support payments in these circumstances. See 750 ILCS 5/505(a)(3.8). It is very important to understand how the parenting schedule will affect Child Support payments and you should hire an Attorney if you have questions.

How Are Child Support Payments Calculated in Illinois?

Illinois statute dictates the procedure for calculating Child Support Payments. While there are important exceptions and situations where the standard calculations may not apply, the standard calculation is computed as follows:

1. Calculate Gross Income and Net Income for Each Parent. The statute provides details for what is included in "Gross Income" for purposes of calculating Child Support. See 750 ILCS 5/505(a)(3). After finding the Gross Income for each parent, state law requires that the the Illinois Department of Healthcare and Family Services must "promulgate a standardized net income conversion table that computes net income by deducting the standardized tax amount from gross income." See 750 ILCS 5/505(a)(3)(C)(II). The Illinois Department of Healthcare and Family Services has published a copy of the 2025 Gross Income to Net Income Conversion Table on their website and updates it each year.

2. Calculate the Basic Support Obligation. Illinois statute requires the calculation of the "Basic Child Support Obligation" which "reflects the percentage of combined net income that parents living in the same household in this State ordinarily spend on their child". See 750 ILCS 5/505(a)(1). The Illinois Department of Healthcare and Family Services publishes a separate Schedule of Basic Obligations (Appendix B, starts on page 24) that lists the Basic Child Support Obligation based on the combined net income of the parents.

3. Calculate Each Parent's Share of the Basic Support Obligation. This calculation is done based on the percent of net income attributable to each parent. The custodial parent (the parent with majority of parenting time) is presumed to spend their share directly on the child or children, and thus is not required to make any payments:

Although a monetary obligation is computed for each parent as child support, the receiving parent's share is not payable to the other parent and is presumed to be spent directly on the child. See 750 ILCS 5/505(a)(1.5).

As a practical matter, due to the inherent complexity, most Attorneys and Courts use specialized software to make these calculations. The Illinois Department of Healthcare and Family Services provides a publically accessible Illinois Child Support Estimator for this purpose but it is almost always a good idea to consult with an attorney because these tools can be used incorrectly cause costly mistakes.

How Long are Child Support Payments Required in Illinois?

Child Support) to make payments until the child turns 18 or graduates high school (if this is after they turn 18) or 19:

The termination date shall be no earlier than the date on which the child covered by the order will attain the age of 18. However, if the child will not graduate from high school until after attaining the age of 18, then the termination date shall be no earlier than the earlier of the date on which the child's high school graduation will occur or the date on which the child will attain the age of 19. See 750 ILCS 5/505(g).

Thus as a general rule, obligations cease when the child turns 18 or graduates high school. Parents are usually not required to support the child after this point and are generally not required to contribut to ongoing living expenses or educational/college expenses. This may not always be the case, however. If the parents signed a valid agreement or if the child has special needs requiring care beyond when they turn 18, the parents may be obligated to continue providing financial support.

You should always consult with an attorney if you have questions regarding child support obligations in Illinois.