Illinois Child Support Calculator

How is Child Support Calculated in Illinois?

Illinois calculates child support by combining both of your net incomes to find a basic support amount from a state schedule. Your share of that amount is based on your percentage of the combined income, a process governed by 750 ILCS 5/505 of the Illinois Marriage and Dissolution of Marriage Act.

Understanding IL's Shared Parenting Time Adjustment

In Illinois, if each parent has the child for at least 146 overnights per year (40% of the time), a special shared physical care formula is used. Under 750 ILCS 5/505, the basic support obligation is multiplied by 1.5 to account for duplicated expenses in two homes. The final amount is then calculated by offsetting each parent's obligation based on their income share and the percentage of time the other parent has the child.

Calculate Your Support

✓ Verified for 2026 Guidelines • Reviewed October 2026 by Harmoney

Illinois Child Support Guidelines at a Glance

Guideline Model Income Shares Model
Governing Legal Authority 750 ILCS 5/505
Shared Custody Threshold 146 Overnights (40% time)
Age Support Ends Age 18 (or 19 if in High School)
Modification Standard Substantial Change in Circumstances

Illinois Child Support: Frequently Asked Questions


At what age does child support end in IL?

Child support in Illinois generally terminates when a child turns 18, but it extends to age 19 if the child is still attending high school full-time. This rule is established under section 750 ILCS 5/513 of the Illinois Marriage and Dissolution of Marriage Act.

How is child support calculated if one parent is unemployed in IL?

If a parent is voluntarily unemployed or underemployed, an Illinois court will impute income to them based on their potential earning capacity and prior work history. This practice, authorized by 750 ILCS 5/505, ensures child support is calculated based on what the parent could and should be earning.

How do I modify a child support order in IL?

To modify a child support order in Illinois, you must prove a 'substantial change in circumstances' has occurred since the last order was entered. Under 750 ILCS 5/510, a new calculation that results in at least a 20% change from the current support amount is typically considered a substantial change, but any significant change in income or needs can be a basis for modification.

Does IL child support cover college expenses?

Yes, Illinois courts can order parents to contribute to a child's post-secondary educational expenses, including college tuition, housing, and fees. This is not automatic but can be requested by either parent and is governed by the specific provisions of 750 ILCS 5/513.

How does IL handle health insurance and childcare costs?

Health insurance premiums and work-related childcare costs are considered separate, add-on expenses that are divided between the parents in proportion to their respective shares of the combined net income. As outlined in 750 ILCS 5/505, these costs are added to the basic child support obligation to determine the final order.