How Will Child Support Be Calculated in Your Illinois Custody Case?

 Posted on May 22, 2026 in Family Law

Many parents assume the child support amount set by the court is entirely up to a judge's discretion. In reality, Illinois uses a specific formula to calculate it based on the family’s income and the child’s needs.

If you're facing a child support determination in 2026, a Kane County, IL child support lawyer can help you understand how the formula applies to your case.

What is Illinois’ Formula for Child Support Calculations?

Illinois uses what's called the "income shares" model found in law 750 ILCS 5/505. The idea behind this model is that a child should receive the same amount of parental support they would have gotten if the family had stayed together. To get there, the court looks at both parents' finances rather than just the paying parent's.

The court goes through the following steps to find the baseline child support amount:

• Both parents' gross incomes are converted to net income by subtracting taxes, Social Security, and certain other deductions.

• The two net incomes are added together to get a combined monthly net income.

• The court looks at the Illinois Schedule of Basic Child Support Obligations to find the baseline support amount for that income level and number of children. The Child Support Obligations schedule is a table published by the Illinois Department of Healthcare and Family Services with up-to-date information about how much it costs to raise a child at a certain income level.

• Each parent's share of the total child support amount is then calculated based on their percentage of the combined income.

This system means that the higher-earning parent will often end up paying more support. However, the burden of supporting the child doesn’t fall completely on them.

What Can Affect the Final Child Support Amount in Illinois?

The baseline number from the schedule is a starting point rather than the final amount. Illinois courts can adjust child support based on additional expenses and circumstances.

Add-on expenses are typically split between parents in proportion to their income. These can include:

• Health insurance premiums for the child

• Unreimbursed medical or dental expenses

• Childcare costs related to a parent's work schedule or job search

• Extracurricular activities and educational expenses, in some cases

Parenting time also plays a role. When both parents have at least 146 overnight visits with the child per year (roughly equal parenting time), Illinois applies a shared parenting adjustment. This can significantly reduce or shift the support obligation. This accounts for the fact that the more time a parent spends with the child, the more they're contributing to the child's daily costs.

Courts can also deviate from the guidelines entirely if applying the standard formula wouldn’t serve the child's best interests (750 ILCS 5/505(a)(2)). This might apply in cases involving a child with significant medical needs, a parent with an unusually inconsistent income, or anything else that the set rate of the formula can’t account for.

Can Child Support Be Modified After It's Set in Illinois?

Either parent can petition the court to modify a support order if there has been a substantial change in circumstances since the order was entered. Common reasons include a significant change in either parent's income, a change in the child's needs, or a change in the parenting time arrangement.

Illinois courts can also review child support orders every three years at the parents’ request, even without showing a substantial change. Courts understand that the amount of financial support kids need fluctuates as they grow and work to accommodate that with the three-year review window.

Call a Kane County, IL Child Support Lawyer Today

Child support calculations may change significantly depending on how income, parenting time, and add-on expenses are presented to the court. If you’re concerned about getting enough support for your children, having professional legal counsel can put your mind at ease. Call Serrano Hanson & Hurtado, LLC at 630-844-8781 to schedule your free consultation with our Geneva, IL family law attorneys today.

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