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Dominika Purcha

Determining how much child support for 1 child in Illinois involves more than just a simple figure. It’s a dynamic calculation that takes into account the net incomes of both parents, the number of overnights with each parent, and several additional costs. This guide aims to demystify the process, aiding you to grasp the principles that lead to the final monthly amount without the fluff.

Illinois puts one child's basic child support level at $1,215 per month; however, this number is a starting point on which additional factors are added or subtracted. Relevant factors must be considered and calculated to understand better what a person may pay in child support in Illinois.  

What is the Income Share Model?

As of July 1, 2017, Illinois has adopted the income shares model as the standardized method and statutory guideline for calculating child support. The income shares model is the starting point for calculating child support which judges consider along with other extraordinary factors, such as an agreement by the parents to a different child support arrangement, the cost of extracurricular activities, and the child's standard of living.  

Why Do We Use The Income Shares Model?

The idea behind the income shares model is that both parents are obligated to provide financial support for their child(ren) as well as emotional support. Their combined income and the total number of children are used to calculate the total Basic Child Support Obligation that a family with the same income and the same number of children should be spending on supporting each child. This total obligation is then divided into each parent's portion of the support by using each parent's respective percentage proportional to the total combined income.  

Keep Reading To Find Out More About:

  • What is the formula for calculating child support?  
  • Sample child support calculations using the Income Shares Model.  

Is There A Formula For Calculating Child Support In Illinois?

The formula to calculate child support is lengthy and complicated when there are many special expenses for the child's needs and/or the child's standard of living. However, it is intended to calculate the basic obligations based on an average family with the same income and the same number of children.  

Be cautious when understanding the estimated child support because your actual child support payments may vary from the estimated due to each individual's unique case facts. Please speak with one of our attorneys at O'Flaherty Law, P.C. to confirm the estimated child support payments that you calculated using the estimator provided by the Illinois Department of Health and Family Services, and keep in mind that things like parenting time with each parent affect the child's well-being, and therefore are taken into consideration by Judges in Illinois when determining child support.  

Let's try understanding the Income Shares Model by reviewing a few examples.  


  • Parent A earns a $30,000 gross yearly income.
  • Parent B earns a $70,000 gross yearly income.
  • They have one child.

The Parents have shared physical care because the child spends 183 nights per year with Parent A and 182 nights per year with Parent B, and no extraordinary circumstances exist.  

The Illinois Department of Health and Family Services estimator will convert your gross income into next income using standard deductions, some of which have changed for the tax year 2020.  

The estimated basic support obligation for both Parents using this scenario is approximately $1,068 monthly; however, because the parents have nearly evenly split parenting time, the income shares model provides for an adjustment called the Shared Physical Care Support Obligation.  

Using the above scenario, the Shared Physical Care Support Obligation is $1,602.00. Parent A's income share is 32%. Parent B's income share is 68%. Parent A's share of the Shared Physical Care Support Obligation is $512.64, and Parent B's share is $1089.36. However, because the parents share nearly equal parenting time, this obligation is adjusted to include this special consideration by being multiplied by the percentage of time with each respective parent, resulting in parent B having a child support obligation of $290,61.  

Mom filling out child support documents with daughter

When it comes to calculating child support, it’s not just about the parents’ income. Other child-related expenses significantly influence the final child support amount. In Illinois, these additional costs, such as child care expenses, are divided between the parents in proportion to their respective shares of combined net income.

Furthermore, the following expenses are typically included in the basic child support obligation:

  • Health insurance premiums
  • Unreimbursed medical expenses, including dental, vision, or orthodontic costs not covered by insurance
  • Educational expenses, such as tuition, books, and other school-related costs

These additional expenses ensure that the child’s overall well-being is catered to in the child support agreement.

Don't Forget The Mandatory Health Insurance!

Additionally, as of 2022, it is obligatory that all parents of a child involved in a domestic relations court proceeding, including custody and support, must provide their child with health insurance. It is both parents' obligation that such health insurance is provided and maintained for at least the duration of the proceedings.  

The Illinois Department of Health and Family Services child support estimator provides that an estimated insurance cost for one child is approximately $87.25 in 2022, but remember that this is just an estimate. The actual cost of health insurance may vary based on the number of people covered by the health plan, the type of insurance plan (PPO or HMO), region, and provider.  

Using the scenario analysis in example 1 above, Parent A would be required to contribute $27.92, and parent B would be required to contribute $59.33 towards the child's health insurance premium each month. However, it is presumed that Parent A automatically contributed towards the health insurance premium, so Parent B is required to pay $59.33 as a health insurance obligation in addition to the child support obligation.  


The following is a more common scenario in Illinois: Parent A earns $30,000 gross yearly income, parent B earns $70,000 gross yearly income, and they have one child. The parents DO NOT have shared physical care because the child spends 243 nights per year (2/3 of the year) with Parent A and 122 nights per year (1/3 of the year) with Parent B, and no extraordinary circumstances or costs exist.  

The income share model calculated that the Basic Child Support Obligation is $1,068.00. Parent A is responsible for contributing $341.76, and Parent B is responsible for contributing $726.24 per month in addition to the health insurance obligation contribution. It is presumed that the custodial parent with the smaller share contribution will contribute their share automatically; the non-custodial parent is obligated to pay $726.24 plus $59.33 in Example 2's scenario.  

Disclaimer: Your circumstances may vary and result in a different support obligation than described in the above sample scenarios.  

What Is The Average Child Support For One Child In Illinois?

The average child support in Illinois is irrelevant to calculating support for one child because the current child support calculations are based on several case-specific factors, such as the parents' total income and the child's standard of living. For advice related to estimated child support payments, contact one of our attorneys at O'Flaherty Law P.C.  

Is There A Cap On Child Support In Illinois?

OLD Illinois law used to provide a cap on child support based on the payor parent's income and the number of children. However, this cap IS NOT applicable as of July 1, 2017, when the income shares model was adopted. Now, the courts will instead consider a more totality of circumstances approach including but not limited to the child's financial needs, extracurricular activity expenses, child care expenses, and the child's standard of living.  

The 2022 Income Shares Schedule Based on Net Income provides a maximum of $2,241 in basic child support obligation, but this is merely a guideline based on a combined income of approximately $30,024.99 monthly and no consideration for extraordinary expenses. $2,241 is not the maximum per child, child support in Illinois.  

Keep reading to find out more about:

  • Does Illinois still use percentage standards when determining child support?  
  • Does the Income Based Model use the gross or net income of the parents when calculating child support?  
  • My income has drastically changed; can I request a modification of my child support obligation?  

What Is The Standard Child Support Percentage In Illinois?

As of July 1, 2017, Illinois no longer considers a standard child support percentage. Instead, the courts now use a more holistic approach: the income-based model. The courts will generally use each parent's respective percentage of their combined income and each parent's respective parenting time percentage when calculating child support.  

Are Child Support Payments Based On Gross Or Net Income In Illinois?

Ultimately the income shares-based model uses the net income to calculate the Basic Support Obligation and then each parent's share of this Basic Support Obligation. However, the Illinois Department of Healthcare and Family Services child support estimator mentioned above and the 2022 Addendum to the Illinois Schedule for Basic Obligations and Standardized Net Income Table provides guidance for quick gross income to net income conversion using standardized federal and state tax deductions.  

Remember that if you use itemized tax deductions instead of the standard deductions when filing your tax returns, your net income may be different than that listed in the above Addendum or that used in the child support payment estimator. Therefore, when determining your child support, you will use itemized deductions to calculate your net income for the purpose of the Income Shares based model.  

Utilizing the Illinois Child Support Calculator

The Illinois Child Support Calculator is a beneficial tool designed to provide an estimate of child support payments. To use this calculator, individuals simply input details regarding both parents’ income, the number of children, and the amount of parenting time each parent has.

The calculator utilizes a methodology that involves:

  • Taking each parent’s adjusted net income
  • Dividing it by the combined net income
  • Calculating each parent’s proportional contribution
  • Determining estimated child support payments

It’s important to note that while the calculator provides an estimate based on Illinois child support laws, the actual child support amount may vary depending on individual circumstances.

What If My Income Changed? Can I Request A Modification?

Child support may only be modified when there is a substantial change in circumstances, either in the child's needs or in the parents' income. An adverse change in circumstances related to the parent's income must be involuntary and, through no fault of the parent, to be considered for modification of support. A substantial change in circumstances must create at least a 20% change in support payments; anything resulting in less than 20% in support obligations is not a substantial change as defined by Illinois statute.  For more information on modification of child support read our article, How Do I Petition For More Child Support In Illinois?

Frequently Asked Questions

Will there be new child support laws in Illinois in 2023?

Yes, the new child support laws in Illinois for 2023 will be based on the BR5 schedule using the latest Betson study, which was published in 2021.

Does child support go down if the father has another baby in Illinois?

Yes, child support may go down if the father has another baby in Illinois, as it could affect the child support calculation. However, it will only change if a party relevant to the case files for a modification.

How are child support arrears calculated in Illinois?

In Illinois, child support arrears are calculated based on the unpaid child support amount plus 9% interest. For example, if a parent fails to pay $1,000 in child support for one year, the arrearage balance would be $1,090.

How much is monthly child support in Illinois?

In Illinois, the monthly child support for one child is $1,215, as per the state's basic support obligation.

What is the standard child support obligation for one child in Illinois?

The standard child support obligation for one child in Illinois is $1,215 per month.

Disclaimer: The information provided on this blog is intended for general informational purposes only and should not be construed as legal advice on any subject matter. This information is not intended to create, and receipt or viewing does not constitute an attorney-client relationship. Each individual's legal needs are unique, and these materials may not be applicable to your legal situation. Always seek the advice of a competent attorney with any questions you may have regarding a legal issue. Do not disregard professional legal advice or delay in seeking it because of something you have read on this blog.

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