How Is Child Support Calculated in Illinois?

 Posted on May 24, 2026 in Child Support

If you are going through a divorce in 2026 and share children with your spouse, child support is probably one of the first things on your mind. How much will you pay, or receive? How does the court decide? 

This is not a niche concern. According to the U.S. Department of Health and Human Services, the national child support program served 12.2 million children in fiscal year 2024, roughly one in six children in the country. That scale reflects just how many families face these same questions. 

Illinois law provides a clear framework for calculating child support in most cases, but the details can be surprisingly complicated. A Wheaton, IL child support attorney at Smit Zaruba P.C. can help you understand what to expect.

How Illinois Calculates Child Support Using the Income Shares Model

Illinois uses what is called the income shares model to set child support. Under 750 ILCS 5/505 of the Illinois Marriage and Dissolution of Marriage Act, the court looks at both parents' incomes, not just the paying parent's. 

The process works like this:

• The court calculates each parent's monthly net income, which is gross income minus taxes, Social Security, Medicare, and certain other deductions.

• The two net incomes are combined into a single number.

• The court uses the state's Schedule of Basic Child Support Obligations to find the total both parents are expected to contribute for that income level, number of children, and amount of parenting time each parent has with each child.

• Each parent's share of that total is proportional to their share of the combined income.

The Illinois Department of Healthcare and Family Services updates the income schedule each year. The most recent revision took effect March 20, 2026. According to the Illinois Department of Healthcare and Family Services, this annual update process has been in place since 2024. It is designed to keep support amounts in line with current economic conditions.

Does Parenting Time Affect the Amount of Child Support in Illinois?

Parenting time plays a significant role in calculating support. When a parent has the child for at least 146 overnights per year, or roughly 40 percent of the time, Illinois applies a shared parenting formula under 750 ILCS 5/505(a)(3.8). This formula accounts for the fact that both parents are spending comparable amounts of money on the child directly.

Even with an equal split, child support rarely drops to zero. If one parent earns significantly more than the other, that parent will likely still owe support. The income difference, not just the parenting schedule, drives the final number.

What Additional Expenses Can Be Added to a Child Support Order in Illinois?

Basic child support covers regular living expenses. Illinois courts can also order parents to share certain additional costs. These are split in proportion to each parent's income and may include health insurance premiums, uninsured medical and dental costs, work-related childcare, and extraordinary educational or developmental expenses. For example, if your child attends a specialized program or needs ongoing therapy, those costs can be added on top of the base support amount. This keeps each parent's share tied to their actual ability to pay.

When Can Child Support Be Modified in Illinois?

A child support order is not permanent. Illinois allows modification when there has been a substantial change in circumstances. Common reasons include a major shift in either parent's income, a change in the child's needs, or a significant change in the parenting time schedule.

Under 750 ILCS 5/510, parents receiving Illinois child support enforcement services may request a review of their order at least once every three years. If the recalculated amount differs from the current order by at least 20 percent, the order may be modified.

Speak with a Wheaton, IL Child Support Lawyer Today

Child support questions rarely have simple answers. Incomes vary, parenting time shifts, and circumstances change. The Lake County, IL family law lawyers at Smit Zaruba P.C. bring over 45 years of combined experience to every case they handle. Whether you are setting up a new order or seeking a modification, having skilled legal counsel can make a real difference in the outcome. Call 630-480-7600 to speak with an attorney today.