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IL Child Support Calculator: (2017 - 2019) New Income Shares Model

Posted by Dominick R. Dolci | Oct 28, 2016 | 0 Comments

The passage of Public Act 99-764 will create big changes in child support obligations for Illinois parents. On August 12, 2016, Governor Rauner signed Illinois House Bill (HB) 3982, amending the Illinois Marriage and Dissolution of Marriage Act (IMDMA).  

This new legislation, which goes into effect on July 1, 2017, will completely change the way child support is calculated in Illinois. Rather than relying on the net income of the non-custodial parent, the new law will introduce an income-share system which relies on a more comprehensive set of factors when calculating child support. Read about the changes and use our IL child support calculator to estimate the award in your case. Then, give us a call to discuss the details of your case.
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Prior to the signing of HB 3982, Illinois underwent several major family law changes, including the introduction of new child custody laws which replace the term ‘custody' with ‘parental responsibilities.' These changes are part of a total overhaul of the IMDMA by the Illinois Family Law Study Committee, assembled in 2008 to examine and improve upon family law in Illinois. This committee — which includes legislators, family law attorneys, child advocacy professionals, and psychologists — conducted extensive studies and hearings on ways the IMDMA could be improved.

The new formula for calculating Illinois child support makes Illinois the 40th state to adopt a child support guideline based on an income shares model.


The Illinois Department of Healthcare and Family Services (IHFS) has recently released schedules and overviews of the new income shares model, going into effect on July 1, 2017.

To access schedules for income conversion and child support obligations and to learn more about these new child support updates, take a look at our overview of income shares.

Illinois Child Support Formula: Pre – July 1, 2017

Until the new legislation takes effect on July 1, 2017, child support in Illinois is still calculated by a formula which depends on the obligor's (non-custodial parent's) income. The basic child support formula uses the number of children to determine a guideline percentage, which is applied to the obligor's net income.

IL Child Support Income Percentages Based on Number of Children

  • One Child = 20%
  • Two Children = 28%
  • Three Children = 32%
  • Four Children = 45%
  • Five Children = 50%
  • Six or More Children = 50%

The amount of child support obligation in Illinois is calculated from the net income of the obligor – the income value after taxes have been paid. While there are other factors that may affect the final child support obligation, the formula above is generally an accurate guideline for most Illinois Child Support cases.

New (2017) Income Shares Model for Illinois Child Support

The new income shares model for Illinois child support calculations is intended to hold both parents accountable for child support, rather than only the non-custodial (obligor) parent. Under the income shares model, parents are designated a portion of child support obligations depending on how much they financially contributed to the combined household income while married.

3 Main Factors Considered in Income Shares Model Child Support Calculation

  1. Basic Child Support Obligation – A combined value of child support owed by both parents together, which is then divided proportionally between the parents based on their individual contribution to a combined household net income.
  2. Additional Expenses – Other costs, determined by the court, which are added on top of the basic child support obligation. These can include child care costsextra curricular activities and outstanding medical or health insurance expenses.
  3. Parenting Time – The amount of time the child spends with each parent. This determines which parent received child support. Additionally, shared parenting situations can lead to some variations when calculating child support based on the new income shares model.

As the law hasn't gone into effect yet, the state of Illinois is still in the process of developing official schedules, worksheets, and formulas for calculating child support obligations. While the specific order of operations for calculating child support has not been finalized, the general formula for determining each parent's child support obligation is known.

General Child Support Formula: IL 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.

How to Calculate Basic Child Support Obligation in Illinois

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.

Example of IL 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%.

Because the new child support law has yet to go into effect, Illinois Healthcare and Family Services is still in the process of developing an Illinois schedule.

Calculating Additional Child Support Expenses

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.

Illinois Child Support Calculation in Cases of Shared Parenting

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.

IL Child Support Calculator for Cases of Shared Parenting

The Illinois Child Support Calculator in Cases of Shared Parenting may look something like this:

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.

Benefits of the Income Shares Model for Calculating Child Support

One of the biggest pros of the income shares model is that it holds both parents accountable when both parents have income. Previously, the non-custodial parent would be required to pay a percentage of his income. With the new model, both parents can get more reliable and realistic calculations of their child support obligation. Both parents are less likely to end up paying more than what they should be.

Because the income shares model relies on the percent each parent contributes to a combined household income, the child support orders calculated under it strongly mimic and preserve the child's lifestyle from before the divorce. Ideally, parents end up contributing close to the same percentage of child care they would if still married. The child would get the same proportion of contributions from each parent as they would if the parents were still married. As a result, the income shares model is usually more beneficial for the child compared to other models, and least disruptive to their life.

How Will Illinois Transition to New Child Support Formula?

The new law going into effect on July 1, 2017 does not automatically change the terms of a child support agreement or order. The change in law alone is not enough to warrant a change or modification of a judgement on a previous child support order. However, changes in circumstances aside from just a new law can make a case for changing child support order. This includes any significant changes in income, finances, or the needs of the child. However, passage of this law may still result in many petitions to modify child support orders. If you are an obligor or recipient of child support, you may want to know if you can modify your order under the new law, or you may be facing a petition from the other party.

Contact our Top DuPage Child Support Lawyers

In any case, a family law attorney who is familiar with the old and new child support laws can offer you legal advice and representation when dealing with a child support case. If you used our IL child support calculator and are looking to find out how this major overhaul of child support in Illinois truly affects your child support case, the family law and child support lawyers at Dolci & Weiland can answer your questions and provide legal assistance. With over 26 years of experience in family law, we are prepared to help you make informed legal decisions, offer expert advice, and protect the interests of you and your family. To speak to a child support lawyer, contact us at (630) 261-9098.

About the Author

Dominick R. Dolci

Managing Partner Dominick R. Dolci focuses his practice on criminal defense litigation and civil litigation. Dom graduated from John Marshall law school in 1990. He began his legal training in the Cook County States Attorneys Office where he worked at 26th and California. He then transferred ...


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