How Is Child Support Calculated in Illinois?

Child support in Illinois is not a number pulled out of thin air. It follows a specific formula — called the income shares model — that is designed to ensure both parents contribute to the cost of raising their children in proportion to their income. Here's how it actually works.

The Income Shares Model

Illinois moved to the income shares model in 2017. The basic idea is straightforward: both parents' incomes are combined to determine what the child would have received if the family had stayed together, and each parent contributes their proportional share of that amount.

What Goes Into the Calculation

• Net income of both parents — gross income minus allowable deductions including taxes, Social Security, and prior child support obligations
• Number of children — the basic support obligation increases with each child
• Parenting time — if both parents have significant parenting time, a shared physical care calculation may apply
• Work-related childcare costs — added on top of the basic obligation
• Health insurance premiums — the cost of the child's portion is allocated between parents
• Extraordinary medical expenses — significant uninsured medical costs are typically split proportionally

What Counts as Income?

Illinois takes a broad view of income. It includes wages, salaries, commissions, bonuses, self-employment income, rental income, investment income, and in some cases imputed income — meaning what a parent could earn if they were employed at their full capacity. If a parent is voluntarily underemployed or unemployed, the court may calculate support based on what they should be earning.

Can Parents Agree on a Different Amount?

Yes — in an uncontested dissolution, parents can agree to a child support amount that differs from the guideline calculation. However, the court must approve it and will only do so if the agreed amount is in the best interest of the child and meets the child's needs. Any deviation from the guidelines must be explained in writing.

When Can Child Support Be Modified?

Either parent can request a modification if there has been a substantial change in circumstances — such as a significant change in income, job loss, or a change in the child's needs. In Illinois, support orders can also be reviewed every three years without showing a substantial change.

Serving Metro East & Southwestern Illinois

Skyy Law Solutions handles uncontested dissolutions throughout Metro East Illinois — including Madison County and St. Clair County. Belleville, Edwardsville, O'Fallon, Fairview Heights, Collinsville, Swansea, and surrounding communities. Flat-fee pricing, evening and weekend appointments available.