The “Income Shares” approach in calculating child support in Illinois

In the fall of 2016, the Illinois Legislature passed and the Governor signed a new statute that completely changes the way child support is calculated in Illinois. The new law took effect July 1, 2017.

Basic Child Support Calculation:

The law eliminates the former percentages and creates what is called the income shares approach. The statute provides reasoning “to calculate child support based upon the parent’s combined adjusted net income estimated to have been allocated to the child if the parents and children were living in an intact household.”

The Illinois Department of Health Care and Family Services established child support guidelines, which include worksheets for calculating the child support and a table to show the percentage of the combined net income “the parents living in the same household in this State ordinarily spend on their children.”

The basic child support obligation is a monetary value. This value is calculated based on a state-provided guideline or table, also known as a schedule. Regardless of other expenditure factors or parenting time distribution, all child support determinations start with using the Illinois schedule.

The schedule cross references the combined net income of the two parents with the number of children they have. The child support schedule uses net income — the income after federal and state taxes — instead of gross income which is the value before taxes. The resulting value calculated from combined net income and number of children is referred to as the basic child support obligationThis basic obligation is prorated between the parents based on the percentage they individually contribute to the combined net income.

Child Support Calculation Based on Income Shares Model:

Take a household with a combined income of $10,000.

Let’s say the both spouses each contribute $5000 of that combined income, or 50%. Without extenuating circumstances, each spouse would be responsible for half of the basic child support obligation.

However, if spouse 1 contributes $6000, and spouse 2 contributes $4000, spouse 1 would most likely be responsible for 60% of the basic child support obligation, while spouse 2 would be responsible for 40%.

For another example: If there are two children, and if based on the combined income of the parents, $50,000 annually is spent on the two children, and if the father has 40% of the combined income and the mother 60%, and if the father is to pay child support, he would pay 40% of the $50,000 or $20,000 annually.

Child Support Calculator (Income Shares Model)

(Basic child support obligation x Percent contributed to combined net income)
(Additional expenses ordered by court x Percent contributed to combined net income)
Total Child Support Obligation

The non-custodial parent then is required to pay their total child support obligation to the custodial parent. While Illinois has discarded the concept of child custody in recent laws, the term custodial parent is used in this case to refer to which parent the child resides with the most, in any non-shared parenting situation.

In a shared parenting situation, there are additional steps taken when calculating child support obligations, which will be explained in detail later.

For the first time, the new statute makes it explicitly clear that spousal maintenance/alimony received pursuant to a court order is income for child support purposes.

Also, if a parent is unemployed or underemployed voluntarily, there is a rebuttable presumption that the income is “75% of the most recent United States Department of Health and Human Services Federal Poverty Guidelines for a family of one person.” There is also “a rebuttable presumption that a minimum child support obligation of $40.00 per month per child, will be entered…”

Child-Related Contributions in addition to child support:

Additional child care expenses that can be added to the basic child support obligation include:

  • Extracurricular activities and school expenses
  • Child care costs
  • Health insurance premiums
  • Outstanding medical expenses
  • Other outstanding expenses related to childcare

Calculating additional expenses is much like the process of calculating the basic child support obligation. The difference is that additional expenses are not calculated from a schedule. Instead, additional expenses from each parent are added together to create a total. That total is prorated based on each parent’s percentage of contribution to the household’s combined net income to calculate how much each parent should pay out of that total.

Each individual parent’s additional expense obligation is added to their basic child support obligation to come up with their total child support obligation.

Child Support Calculation in Cases of Shared Parenting Time:

In Illinois, shared parenting is when each parent spends at least 146 (or 40%) of overnights with their child each year. Any child support case which does not meet these terms of shared parenting are calculated with the regular formula.

However, if each parent spends at least 146 or 40% of nights per year with their child, then the total child support obligation is calculated differently.

How to calculate parenting time allocation:  Assume that the winter break from school is two weeks, the spring break is one week, and each parent gets two weeks of vacation during the summer, which leaves 45 weeks in the year. If each parent gets two weeks in the summer plus half of the winter break, then each parent starts with 21 days. A parent would then need 125 additional days to get to 146 days. If the parties alternated the spring break, then they would each have 3.5 days. Then a parent would need 121.5 overnights in a year. Divide that by 45 weeks remaining in the year, then a parent would need three overnights out of seven for the rest of the year in order to reach 146 nights.

The potential for parents to significantly argue about getting both of them to 146 nights minimum turns into a financial one rather than a consideration of what parenting plan may be best for the children. It can easily be foreseen that one parent will significantly and strenuously argue that the other parent should not reach 146 nights and the parent who wishes that will strenuously argue for it. A Judge may need to attempt to determine if the reason for seeking 146 is merely to save child support.

The basic child support obligation is still found on the schedule based on the number of children and the combined net income of the two parents. However, the basic child support obligation is multiplied by 1.5 to account for duplicate expenses and the price of transportation between the two residences. This new value is referred to as the shared care support obligation.

The shared care support obligation is prorated based on each parent’s percentage of contribution to the combined net income. The resulting value for each parent is called their child support obligation.

Each parent’s child support obligation is multiplied with the other parent’s percentage of parenting time produce an individual obligation for each parent.

Basic child support obligation x 1.5
= Shared care support obligation

Shared care support obligation x Percentage of contribution to combined net income
= Child support obligation

Child support obligation x Opposite parent’s percentage of parenting time
= Individual child support obligation

Unlike in non-shared parenting cases where the non-custodial parent pays their obligation to the custodial parent, those in a shared parenting situation are close to having equal parenting time with their child. Therefore, there is no pre-determined custodial or non-custodial parent.

Instead, individual child support obligations for both parents are offset to find the difference between them. The parent who owes the greater amount of child support is ordered responsible for paying that difference to the parent who owes the lesser amount of child support.

Here are the resources that have been released by the Department of Healthcare and Family Services (with links below):

  • Illinois Child Support Calculator: The Illinois Child Support Estimator is an online tool you can use to estimate the amount of child support you can expect to receive or be obligated to pay under the new law.  It automates the use of the tables and worksheets below.
  • Income Shares Overview:  This tutorial explains the new law and provides an example of how to calculate child support based on case- specific facts under the new income shares model, including how to determine net income of the parents.  The tutorial explains how to use the child support calculator provided on the Department of Healthcare and Family Services’ website.  The tutorial explains how child support is calculated in shared parenting situations and split parenting situations, when child support may be modified, and the Illinois child support minimums and maximums.
  • Gross to Net Income Conversion Table: This table allows you to quickly estimate your net income, upon which child support obligations are based, from your gross income.  This is based on the standardized amount you will be expected to pay in taxes.  Be sure to follow the instructions in the tutorial to determine what qualifies as gross income before using this table. For example child support obligations to another parent, and Supplemental Security Income are not part of your gross income.
  • Income Shares Schedule Based on Net Income:  Once you have calculated the combined monthly net income of both parents, you can use this table to estimate the amount  of the parents’ joint child support obligation.
  • Child Support Obligation Worksheet:  Once you have determined each parent’s net income and the total child support obligation, you can use this  worksheet to determine the amount of each parent’s child support obligation in non shared physical care situations.
  • Shared Physical Care Support Obligation Worksheet: If you are in a shared physical care situation, meaning that both parents have the child for at least 146 overnights per year, you can use this worksheet to calculate each parent’s support obligation.


Former Child Support Law in Illinois:

Under the former law, the amount that an obligor parent was required to pay in child support was based simply on the obligor’s income and the number of children involved.

Under the new “income shares” model for calculating Illinois child support, the total amount of child support for which the parents are jointly responsible is calculated based on the combined net income of both parents.  Once this number is determined, each parent’s share of the responsibility for providing that amount of child support is calculated based on the net incomes of the parents relative to one another.

​​This means that, unlike the previous law, the new child support law takes the income of the recipient of the child support into account when determining the amount of the obligor parent’s child support obligation.