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The Timing of Child Support Modification

The Divorcerer Speaks:  The Timing of Child Support Modification

Has there been a change in your employment or income?  Are you failing to exchange income information and documentation each year?  Was your child support obligation entered prior to the change in Illinois law on July 1, 2017?  If you answered “Yes” to any of these questions then you may need to consider a modification of your child support obligation.

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.

This new “Income Shares” approach calculation is aided by the use of guidelines, tables, worksheets and schedules in calculating, further taking into consideration the allotment of parenting time.

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

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.

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.

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

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.








Jennifer R. Ward has an undergraduate degree from the University of Missouri – Columbia in Journalism and is the founder of WARD FAMILY LAW, LLC.  Ms. Ward was admitted to the Illinois bar in 2002 and continues to exclusively practice matrimonial and family law in the Chicagoland area.  Additionally, Ms. Ward has been Adjunct Faculty at the John Marshall Law School since 2005 and teaches family law legal drafting to law students in a Legal Writing program that U.S. News and World Report ranked as #5 in the Country.  Ms. Ward also had the honor of speaking at the “Leaving a Long-Term Marriage” workshop produced by The Lilac Tree, an Evanston-based not-for-profit resource for women contemplating divorce.

You can find Jennifer R. Ward, Founder of WARD FAMILY LAW, LLC at www.wardfamilylawchicago.com or you can follow her on Facebook @WardFamilyLaw, Instagram @divorcerer, Google Plus @Wardfamilylawchicago and Twitter @WardFamLawIL



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