Factors That Determine Child Support in Illinois

As if figuring out who pays what when it comes to child support wasn’t complicated enough, on July 1, 2017, a major change took place in Illinois.  Public Act 99-764 amended the Illinois Marriage and Dissolution of Marriage Act to replace the old percentage guideline formula with an income shares model already in use in 39 other states and the District of Columbia.  This law is for new cases, but affects older cases that have a change in circumstances.

Instead of relying on the net income of the non-custodial parent to pay the custodial parent, the new law creates an income-share system.  Both parents are now accountable for child support based on how much they financially contributed to the combined household income while married.

The purpose of the new law is to increase fairness by taking into account actual child-rearing costs based in part on data from the Bureau of Labor Statistics. The Illinois Department of Health and Family Services uses that data for its Schedule of Basic Child Support Obligation.

The compassionate and experienced Illinois family-law attorneys at Wolfe & Stec, Ltd., understand the stresses and financial pressures of divorce and recognize the concerns parents have for the well-being of their children.  If you have any issues with how the new law affects your child support calculations, we offer a free initial consultation to examine your individual situation and help come up with solutions that are best for you and your family.

How the New Calculations Work

To calculate child support, the courts now consider the following:

  1. Basic Child Support Obligation – The combined value of child support owed by both parents together. This is then divided proportionally between the parents based on their individual contribution to a combined household net income.
  2. Additional Expenses – Other costs, such as child care and medical costs which are added on top of the basic child support obligation.
  3. Parenting Time – The amount of time the child spends with each parent.

So, the new law uses the net income of both parents in order to calculate the child support due from one parent to the other. Parents can use either of two tax-based formulas to determine their net income, or they can agree to use a different formula if the court agrees.

If both parents are employed, the net income of both parents is combined, and the percentage of child support owed by each party is calculated by the Schedule. If one parent is not employed or is underemployed, the Court can impute income to that parent in order to determine child support.

In calculating the basic child support obligation, both individual net monthly incomes are added together and matched to the Schedule, based on the number of children. Once the basic support obligation is determined, the percentage contribution for each parent is determined by dividing that individual’s monthly net income by the combined monthly net income. So, if combined monthly net income is $10,000 and one parent earns $2,000 and the other $8,000, their percentage contributions would be 20 and 80 percent.

Now parenting time enters the picture.  The parent who has the most parenting time receives the support payment, which is calculated by multiplying the basic support obligation by the payor’s income share. The parent receiving payment would be expected to use their own percentage contribution to care for the child as well.

Shared Parenting Time

There is a formula designed to further reduce the non-majority-time parent’s child support obligation if that parent has the children overnight for 146 or more nights per year (at least 40% of a calendar year). When both parents have 146 or more parenting overnights a year, a shared parenting adjustment kicks in.

First, the basic support obligation is multiplied by 1.5 due to an assumed increase in child-rearing costs for both parents in a shared parenting situation. After the parents’ contributions are calculated, they are adjusted by the percentage of parenting time.

For example, consider what happens if parents of two children make a combined $10,000 net a month, the father makes 70% of that amount and the mother has the kids 55% of the time. If the total basic support figure is $10,000, the combined support obligation from the chart is $2,187. This would be multiplied by 1.5 and then by .7 and .55. The father’s monthly obligation would be $1,262.99, less than he would ordinarily pay because he spends more time with the kids.

If parents share parenting time 50/50, they would find the combined net income figure for both of them on the table, multiply each by 1.5 and then whoever has the higher number pays the difference to the other one.

The new law has not yet addressed every situation.  For example, the table for the net income combination now ends at $30,000 a month.

Changing Circumstances

If you have a change in circumstances, you are allowed to go to court to ask for a modification.  The parent requesting the change must file legal paperwork asking for a change in child support and giving the reasons why.

Parents who get a raise at work may actually wind up paying less if the new formula allows them to do so.  Parents can also agree to modify child support on their own and request that the court approve their proposed change if it satisfies Illinois law.

In Illinois, parents’ obligation to support a child ends when the child turns 18, or until 19 or graduation if the child is still attending high school full-time, or if a child is disabled and not capable of self-support. Judges may also order parents to help with the expenses of a child over 19 who is attending college.


As you can see from the examples above, child support laws can be complicated, especially when changes occur, and you will have to deal with the results for years. If you have questions about the new laws, calculating child support, or modifying or appealing existing support orders, you should contact an attorney to be sure your rights are protected. The skilled Illinois family-law attorneys at Wolfe & Stec, Ltd. know the laws, the courts and the system and can guide you through the process.  We represent and advise clients in all types of child custody matters and have a long history of success.

Don’t delay. For a free initial consultation with an experienced and compassionate DuPage County custody lawyer, contact us online or call 630-305-0222 for a free initial consultation.

Attorney Natalie Stec

Natalie M. Stec, born and raised in Illinois, and earned her Bachelor of Science from the University of Illinois at Urbana-Champaign. Her practice has been concentrated in significant pre and post decree marital and family law cases; including custody, visitation, support, and paternity matters. She has important criminal defense experience in both misdemeanor and felony cases. She is a very dedicated and passionate litigator. [ Attorney Bio ]