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  • Writer's pictureAngela Larimer

How Is Child Support Calculated in Illinois?

Find out how to calculate child support in Illinois. For a free consultation with a child support lawyer in Chicago, call Angela at Larimer Law at 773-370-0600 or email Angela at to set up your free consultation.

Illinois has specific rules in place for calculating the financial support required of both parents, whether married, separated, divorced, or single. Parents have the ability to come to an agreement regarding child support payments, but they are required to adhere to the specific laws and guidelines set by the Illinois legislature.

The Income Shares Model

Prior to 2017, the Illinois courts relied on what was known as a percentage-based child support payment formula. As of July 1, 2017, that model officially changed to one based on income shares. This "income shares model" recognizes that both parents are responsible for financially supporting their child. Therefore, payments are calculated based on both parents' income levels and the number of overnights with the child(ren) that each parent enjoys. The model also takes into account the amount that would be spent on raising children if the child(ren) lived with both parents and the parents shared finances.

Potential Additional Changes

Although the courts in Illinois are required to perform initial child support calculations based on the income shares model for family law cases, they may be able to deviate from the calculation based on certain factors. These factors pertain to what's in the best interest of the children involved and may include the emotional or physical condition of the child, the standard of living the child would have enjoyed if he or she lived in a household with both parents, the specific educational needs of the child, and the child's financial needs and resources, along with the needs and resources of each parent.

In addition to the net income of both parents, additional "add on" expenses for the child are also added into the formula. Those "add on" expenses are:

●Health care

●School expenses


●Extracurricular activities

●Medical expenses

●Extraordinary child related expenses for a child with special needs

Calculations Based on Net Income

Calculating child support on the income shares model will entail adding both parents' net income. The net income is calculated from a parent's income from all sources. The Court subtracts standard adjustments and deductions, including federal and state tax deductions. In cases whereby the parent is a state or civil employee who does not pay into social security, mandatory retirement contributions are also deducted.

To get a better idea of how to calculate child support based on the income shares model, parents can use the Illinois Child Support Estimator during the collaborative divorce process.

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