How child support is calculated in Illinois
The formula, the official tool, and the rules for low incomes and health insurance.
Checked against official sources: Oct 25, 2026.
Short answer
Illinois uses the income-shares model: both parents' incomes count, and each parent pays a share of the child's support. Both parents' net incomes (usually a standardized net income based on ordinary taxes) are added together and looked up in the state schedule to find the basic support obligation.
- Model
- Income shares
- Official calculator
- Official Illinois child support calculator
The official Illinois calculator
Both parents' net incomes (usually a standardized net income based on ordinary taxes) are added together and looked up in the state schedule to find the basic support obligation. Each parent pays a share based on their part of the combined income. Work-related child care can be added. If each parent has 146 or more overnights a year, a shared physical care formula is used.
Law: 750 ILCS 5/505
We don't estimate Illinois's amount here: its formula uses both parents' incomes and other facts, and a home-made number could mislead you. The official tool gives the real starting number:
What goes into support in Illinois
Both parents' net incomes (usually a standardized net income based on ordinary taxes) are added together and looked up in the state schedule to find the basic support obligation. Each parent pays a share based on their part of the combined income. Work-related child care can be added. If each parent has 146 or more overnights a year, a shared physical care formula is used.
Law: 750 ILCS 5/505
What the model means
The income-shares model looks up an amount for the parents' combined income, then splits it by each parent's share of that income. Parenting time and costs can change it.
Every state must have one set of child support guidelines, review them at least every 4 years, and use the guideline amount unless a written finding says it would be unjust.
Law: 45 CFR 302.56
The child's health costs in Illinois
A support order may say which parent must provide health insurance. CSS sends a medical support notice to the employer to enroll the children in coverage.
In nearby states
From income to an order in Illinois
Gather income papers
Pay stubs, tax returns and benefit letters for both parents, if you have them.
Run the official numbers
The state's own tool gives the starting number: Official Illinois child support calculator.
Count health and child care
Insurance and child care often go on top of the basic amount.
Get an order
Only a court or the agency can set the amount. Open a case with Illinois Department of Healthcare and Family Services (HFS), Child Support Services (CSS) (1-800-447-4278) · Apply online
Talk to legal aid
Ask for free help: Illinois Legal Aid Online and Illinois State Bar Association Illinois Lawyer Finder.
Where to get free help in Illinois
Questions about the Illinois guidelines
How is child support calculated in Illinois?
Both parents' net incomes (usually a standardized net income based on ordinary taxes) are added together and looked up in the state schedule to find the basic support obligation. Each parent pays a share based on their part of the combined income. Work-related child care can be added. If each parent has 146 or more overnights a year, a shared physical care formula is used.
Is there an official child support calculator for Illinois?
Is health insurance part of child support in Illinois?
A support order may say which parent must provide health insurance. CSS sends a medical support notice to the employer to enroll the children in coverage.