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Calculate Illinois Child Support Payments

Use the child support calculator below to estimate your child support and medical support payments. Illinois child support is based on a variety of factors including the number of children, the number of overnights with each parent, and each parent’s net income.

How to Calculate Child Support in Illinois

Illinois child support takes many factors into account. The exact calculation is a lengthy process, but our calculator does all the work for you. All you have to do is plug in the numbers, and the calculator estimates your child support payments.

For any questions on what a section of the calculator means, refer to the guide below the calculator. Your actual child support payments may be different than what the calculator estimates because judges have discretion to adjust as necessary. 

These are estimated values and may present inaccurate results for high income individuals, individuals who are self-employed, or have additional income sources. For a more accurate estimate as to support payments, including both child support and maintenance, please schedule a consultation with one of our attorneys.

For Immediate help with your family law case or answering any questions please call (312) 757-8082 now!

Guide to the Child Support Calculator

  • Number of Children = The number of children you have with the opposing party in this case.
  • Number of Overnights with the Custodial Parent = Of the 365 days in the year, how many nights are spent with the custodial parent.
  • Determine Net Using = Chose standardized or individualized for the custodial parent (CP) and non-custodial parent (NCP). Standardized means the person’s gross monthly income (separate spousal maintenance). Individualized is income after taxes are taken out found by using Illinois’s income conversion chart.[1]
  • Maintenance Received/Paid = If either parent receives or pays spousal maintenance (alimony), include that here.
  • Social Security Benefit Allotment = If either parent receives social security checks, record that here.
  • Multi-Family Adjustment with Order = If a parent pays child support through the state for a child with a different mother, the amount paid goes in this section.
  • Children on Multi-family Adjustment with Order = If the above box is filled out, list the number of children they are paying for in this box.
  • Multi-family Adjustment Without Order = Fill out this section if a parent pays child support for a different child, and the child support is not paid through Child Support Services.
  • Children on Multi-family Adjustment Without Order = If the above box is filled out because someone is paying informal child support, list the number of children they are paying for here.
  • Child’s Monthly Health Insurance = Provided means there is currently active insurance. Available means there is the option of having insurance. State whether the insurance is from the custodial parent (CP) or non-custodial parent (NCP), how much it costs, and how many people are covered on the plan.
  • Child Care Expenses = This includes any daycare, after-school care, camps, etc.
  • Extraordinary School and Extracurricular Activity Expenses = Any extra costs for a child’s participation in sports, clubs, field trips, etc.

Potential Deviations

A judge deciding child support can order more or less child support than the state guidelines require. This is called a deviation. They can do this if the support would otherwise be “inequitable, unjust, or inappropriate.”[2] With any deviation, the judge has to provide a written explanation telling why they think the deviation is necessary. One example of this is if the child has a disability that leads to extra expenses.

The best way to ensure fair child support is to have an attorney support you through the process. For any questions, call Sterling Lawyers, LLC or fill out the linked form and we can set you up for a meeting to talk with an attorney who specializes in family law.

Are you ready to move forward? Call (312) 757-8082 to schedule a strategy session with one of our attorneys.

How to Calculate Child Support

Here is a simplified explanation of how the child support calculator estimates child support payments. The actual calculator takes even more factors into account, but this calculation lays out the core of the calculation.

Below each step, there is an example following along. For this example, there are two kids, the custodial parent (CP) has an income of $4,000 per month, and the non-custodial parent (NCP) has an income of $5,000 per month.

Adjusted Net Income

1.) Find each party's gross monthly income and convert it into net income using the IL standardized income conversion chart (found in the first reference link below).


Based on the standardized income chart, CP has a net income of $3,164. NCP’s net income is $3,771.

2.) Then, add the net incomes together to get the parents’ combined adjusted net income.


$3,164 + $3,771 = $6,935.

Total Support Obligation

3.) The state of Illinois says the basic child support for one child is $1,215 per month. Multiply this number by the number of children to get the basic support obligation.


$1,215 x 2 = $2,430

4.) Then, to get the total support obligation, add any extra expenses such as child care, extracurricular activities' expenses, and insurance premiums.


We’ll say it’s $90 for after-school care and $100 for the child’s insurance per month.

$2,430 + $90 + $100 = $2,620

Share of the Obligation

5.) Take each parent’s adjusted net income and divide it by the combined net income to get the percent of their contribution.


CP: $3,164 ÷ $6,935 = 45.6%.

NCP: $3,771 ÷ $6,935 = 54.4%

6.) Multiply that percentage by the total support obligation, and you get the amount each parent must pay towards the child’s support.


CP: 45.6% of $2,430 = $1108.08

NCP: 54.4% of $2,430 = $1321.92

7.) Since in this case, the child lives with CP, NCP has to pay the full amount of their child support.



Now that you know how our calculator works, feel free to click here to head to the calculator of you haven't already.

Calculate Child Support for Shared Parenting (Joint Custody)

Shared parenting is when each parent has at least 146 days with the child. In this case, the courts calculate child support a little differently. For the below example, we use the same numbers as the previous examples. However, CP has the child for 219 days of the year (60%), and NCP has the child for 146 days of the year (40%).

1.) / 2.) First, steps 1 and 2 are the same to get each parent’s net income.

3.) / 4.) Then, for steps 3 and 4, to get the total support obligation, the cost per month of a child is multiplied by 150%. It goes from $1,215 to $1,822.50.


Using the above calculation, their total support is $3,644. ($1,822.5 x 2)

5.) / 6.) Steps 5 and 6 are done the same to get each parent’s share of the obligation.


CP’s portion of the support obligation is $1,661.66. (45.6% x $3,644)

NCPs portion of the support obligation is $1,982.34. (54.4% x $3,644)

7.) Now, rather than finding the difference between their support obligations right away, you first multiply their individual obligations by the percentage of time the other parent has with the child. This finds each parent's new support obligation.


CP’s placement percent multiplied by NCP’s share of the support obligation to get NCP’s new support obligation. (60% x $1,982.34 = $1,189.40)

NCP’s placement percent multiplied by CP’s share of the support obligation to get CP’s new support obligation. (40% x $1,661.66 = $664.66)

8.) Finally, with the two resulting numbers, you take the non-custodial parent’s obligation and subtract the custodial parent’s to get the final child support payment amount. If the number is positive, the non-custodial parent pays that amount. If the number is negative, the custodial parent may have to pay that amount.[3]


In this situation, NCP will have to pay CP $524.74 in child support. ($1,189.40 – $664.66)

Our calculator can estimate child support for joint or sole custody. Click here to head back up to the calculator.

For Immediate help with your family law case or answering any questions please call (312) 757-8082 now!

Frequently Asked Questions

Who pays child support when custody is 50/50?

Even with a joint custody schedule, one party may need to pay child support. If one party makes more than the other, the party making more may have to pay child support. There are many more factors to consider, so the best thing to do is use the above child support calculator.

What is the new law on child support in Illinois?

In 2019, Illinois changed the way child support is calculated to the income shares model. This takes into account the parents' incomes, the number of children, and the cost of living to determine how much it costs to support a child. This method further standardizes child support and makes it fairer because it is based on the specific situation.

How does the court determine the amount of child support?

The court uses the same calculation described above. They determine the total support necessary for the number of children based on the parents’ combined incomes. Then they determine what portion of the support each parent covers. If you need your child support changed, you can also modify child support in some cases.

What is the maximum percentage of child support in Illinois?

Before Illinois updated the laws, they had a parent pay a set amount of their income depending on the number of children they had. Now child support is based on net income, so there is not a specific limit in the same sense.

Does a mother’s income affect child support?

Yes, a mother’s income is used to find the combined adjusted net income which determines the amount of child support each parent is responsible for.

Is child support in Illinois based on gross or net income?

Child support is based on net income. That being said, you get net income from gross income, so gross income can be used to calculate child support.

References: 1. Gross to Net Income Conversion Table. Illinois Department of Healthcare and Family Services. (2019). | 2. 750 ILCS § 5/505 (a)(3.4). Property, Support, and Attorney Fees. | 3. 750 ILCS § 5/505 (a)(3.8).

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