Child Support in Illinois – It’s Not What It Used to Be

Prior to July 1, 2017, child support in Illinois used to be calculated as a percentage of the non-custodial parent’s net income. However, on July 1, 2017, Illinois joined a number of states that utilize an “income shares” model when calculating child support. 

How did Illinois calculate child support previously?

Before July 1, 2017, Illinois utilized a “percentage of income” model when determining child support. Based on the number of children a non-custodial parent had, he or she would pay a percentage of their net income as and for child support. For one child, the non-custodial parent would pay 20% of his or her income; two children, 28%; three children, 32%; four children, 40%; five children, 45%; and six or more children, 50%.  The custodial parent’s income was never taken into consideration in calculating the non-custodial parent’s support obligation. 

What is the “income shares” model?

The income shares model of calculating child support utilizes the income of both parents when calculating the payor’s child support obligation. According to the National Conference of State Legislatures, forty states utilize the income shares model of calculating child support. ( The idea behind utilizing an income shares model is that both parents have a financial obligation to support the children, so both of their incomes should be utilized in calculating a child support obligation.

How is support calculated under the income shared model?

First, determine the net income of both parents. In Illinois, net income has been defined as all income from all sources minus taxes and certain statutory deductions (which include a multi-family adjustment and court-ordered maintenance payments). The taxes should not be the actual amount withheld, but rather as if they were properly calculated as if neither party would receive a refund or owe a liability. In determining income, Illinois also allows for certain money to be excluded from “income from all sources.” The following are not included in the calculation of income for child support purposes in Illinois: benefits received by the parent from means-test tested public assistance programs (such as TANF, Supplemental Security Income, or SNAP) and benefits and income received by a parent for other children in the household, such as child support, survivor benefits, or foster care benefits. 

After determining the net income of both parents, add that together. Once they are added together, you will refer to the schedule of basic child support obligations. This schedule has been created based on actual data for how much families spend on raising children, depending on the number of children and the total net income of the parents. To utilize the schedule, you will find the combined net income amount on the left hand side, and line up the number in that row with the column for the number of children.  This number is the basic support obligation shared between the parties. 

Once you have determined what the “total” support obligation for the parties is, the next step is to determine what percentage of the total net income each parent earns. After you have done this, you will multiply each parent’s percentage by the total basic support obligation, to determine which parent will owe support to the other. Whichever parent has the higher number for their share of the child support will pay that amount to the other parent. The other parent’s share of the obligation is not an offset, as the law contemplates the parent receiving support is already spending whatever their portion is on the child. 

However, if the non-custodial parent has 146 or more overnights in a calendar year, the calculation changes. If that is the case, then each parent’s share will be calculated differently. In order to calculate a parent’s share of support in this shared parenting situation, you will first multiple the basic support obligation by 1.5 and then multiply that number by the percentage of that parent’s share of the total net income. Instead of that being the last step, you will then need to determine what percentage of time the child stays with each parent. After you have done that, you will multiple the parent’s share of the increased basic support obligation by the percentage of time the other parent has parenting time with the child. (For example, if Parent B has 43% of the parenting time with the child, you will multiply Parent A’s share of the increased basic support obligation by 43%). After you have done this step, you will offset the paying parent’s obligation by the recipient parent’s obligation. The theory behind offsetting this amount is because the child is spending so much time with both parents, that both parents are incurring significant expenses in each home providing for the child. 

For More Information

There are additional changes that have occurred with the child support law, but the income shares model is the biggest change that has occurred. There are additional expenses that may be included in a party’s child support obligation. If you would like additional information about co-parenting, contact the Family Law Attorneys at Sterk Family Law to get started.  Please contact our office at 815-600-8950 or contact us online to schedule a free consultation.

This article does not constitute individual legal advice and is to not to be construed as such.  This article contains general information and constitutes legal advertising.


This is a legal advertisement from Sterk Family Law Group. It does not constitute legal advice and should not be construed as such. This article is for informational and educational purposes only.

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