Illinois Child Support Guide (2025)

Sometimes, couples don’t always work out as planned, and if one parent earns more than the other parent, or one parent has the majority of custody, child support is essential, and that includes Illinois. Child support is one of the most important and misunderstood aspects of family law, and the ability to pay or receive fair support is of utmost importance. If you’re a parent seeking support or one expected to pay, understanding how Illinois regulates and calculates child support can save time, stress, and potentially thousands of dollars

This guide walks you through the Illinois child support process in 2025.

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Illinois’ child support laws

Before 2017, Illinois used a percentage-of-obligor model to calculate child support, which was a system in which a non-custodial parent paid a simple flat percentage of their income. The payment depended on the number of children: 20% for one child, 28% for two, and so on. For example, if someone earned $4,000 a month in net income and had two kids, they’d owe around $1,120 in child support under the old system (28% of $4,000). The custodial parent’s income wasn’t factored in at all, and while simple and easy to use, this model was often criticized for being unfair. In situations where the custodial parent earned significantly more or where parenting time was more evenly split, the economic model didn’t make as much sense.

So, people complained, and to better align with national best practices, Illinois overhauled its approach. On July 1, 2017, the state adopted the income shares model, becoming the 40th state in the U.S. to do so. This system more accurately reflects the economic realities of modern parenting by considering both parties’ financial contributions and sharing responsibility for child-related expenses.

How child support is calculated in Illinois

The income shares model

Illinois uses what’s called the income shares model for child support, which is a more accurate and fairer measurement than before. This approach estimates the total cost of raising a child based on both parents’ combined net income, then divides that obligation between them in proportion to their income. The idea is to maintain the child’s standard of living as if both parents were still in the same household.

This model replaced the old percentage-based system and better accounts for both parents’ ability to contribute. It also makes allowances for parenting time, healthcare, child care expenses, and shared custody.

Step-by-step breakdown of Illinois child support

Calculating child support in Illinois may seem formulaic, but it attempts to be as fair as possible. Raising a kid isn’t easy but raising a kid with limited financial means to do so can be a heartbreaking endeavor. The state uses a multi-stage process that takes into account income, shared expenses, and parenting time.

Step 1: Determine each parent’s monthly net income

Child support calculations begin with each parent’s net monthly income, not gross. This means subtracting mandatory deductions from wages and other income, such as:

Federal and state income taxes
Social Security and Medicare
Retirement contributions
Health insurance premiums
Other court-ordered obligations

Parent	Gross Monthly Income	Net Monthly Income
Parent A	$4,500	$3,600
Parent B	$5,500	$4,200
Combined Net Income		$7,800

This combined amount is used to estimate the total monthly child support obligation by referencing the Illinois child support guidelines chart. The chart assigns a baseline support figure based on the number of children and the total net income of both parents. This figure represents what it would reasonably cost to support the child or children in a two-parent household, and it becomes the foundation for determining how much each parent should contribute.

Step 2: Determine the base support obligation

Illinois provides a chart (updated periodically) that lists the basic child support obligation based on the number of children and the parents’ combined net income.

For two children and a combined net income of $7,800, the guideline support obligation might be approximately $1,950 per month. This figure represents the total amount both parents are expected to contribute together to meet the basic needs of the children, including housing, food, transportation, clothing, and other essential living expenses. This amount will then be divided between the parents based on their respective shares of the combined income.

Step 3: Add allowable extra expenses

Along with the base child support obligation, Illinois law allows for the inclusion of certain necessary expenses that directly benefit the child’s well-being. These costs are added to the monthly support figure before each parent’s share is calculated.

These commonly include:

Health insurance premiums specifically attributable to covering the child
Work-related child care expenses, including daycare or after-school programs
Extraordinary medical expenses, such as ongoing therapy or specialized treatment
Educational needs, including private tuition, tutoring, or learning support services

By the numbers

If the base support obligation is $1,950 and the parents incur $120/month in health insurance premiums and $200/month in child care, the total allowable extra expenses would be $320. The adjusted total support obligation would therefore be $1,950 + $320 = $2,270 per month.

Step 4: Determine each parent’s percentage share

So now we have the total support obligation, which is the total cost of raising the child to have his or her needs met., The next step is to determine how that amount will be divided between the parents. This is done by calculating each parent’s percentage share of the combined net income. In simple terms, the parent who earns more will be responsible for a larger portion of the total child support, reflecting their greater financial capacity.

These income percentages are then applied to the total support amount (including the base obligation and any additional expenses) to determine what each parent is expected to contribute. It’s important to note that this step does not automatically mean one parent will make a payment to the other; custody arrangements and parenting time still play a role in how final payments are calculated, as we’ll see in the next steps.

Step 5: Apply the shares to the support obligation

Now that each parent’s percentage share of the combined income has been established, those percentages are applied to the total monthly support obligation, which includes both the base amount and any allowable extra expenses. This step determines the financial responsibility each parent bears for the overall support needs of the child.

Example:

Total monthly obligation (from Step 3): $2,270
Parent A’s share: 46.15% × $2,270 = $1,048.65
Parent B’s share: 53.85% × $2,270 = $1,221.35

In this scenario, if Parent A is the custodial parent and is already covering day-to-day expenses, then Parent B would typically be required to pay their share, $1,221.35 per month, as court-ordered child support.

Income and support comparison: Parent A vs. Parent B

This chart summarizes the key financial data for both parents based on our working example. It provides a side-by-side comparison of gross and net income, income share percentages, and the calculated child support obligations.

Adjusted support comparison with shared parenting time

When parenting time is shared, meaning each parent has the child for at least 146 nights per year, Illinois adjusts the child support calculation to reflect duplicate household expenses. Below is a breakdown of how support obligations shift when Parent A has 55% of parenting time and Parent B has 45%.

Item	Parent A	Parent B
Income Share (%)	46.15%	53.85%
Shared Obligation (1.5 × $1,950)	$1,350	$1,575
Parenting Time (%)	55%	45%
Offset Amount	$1,575 × 55% = $866	$1,350 × 45% = $607
Final Support Adjustment	—	Owes $259/month

While both parents still contribute based on their income, the actual payment owed is reduced by the overlap in parenting time and shared costs. In this case, because Parent A has the child more often, Parent B owes a lower support amount, $259 per month, rather than their full share of the base obligation.

Special circumstances that may affect calculations

While Illinois uses a standardized formula to calculate child support, the law also allows courts to deviate from the guidelines when unique circumstances arise. These deviations are not common, but they can be significant when the standard calculation does not reflect the child’s best interests or the financial realities of the family.

High-income families

In very high-income cases, the guideline charts may not be sufficient to determine a fair support amount. When combined parental income exceeds the highest bracket on the state chart, courts may cap the obligation or make upward adjustments depending on the child’s established lifestyle. Expenses such as private school tuition, travel, extracurricular activities, or a child’s individual needs may justify additional support beyond the standard formula.

Non-income-based deviations

Courts may also adjust child support based on specific situational factors that affect the fairness of the calculation, even when income itself is not the issue.

💡 These include:

Significant debts or obligations owed by either parent, such as supporting children from a previous relationship
Unusual or ongoing expenses related to the child, such as learning disabilities, long-term medical conditions, or therapy
Unemployment or job loss, especially if involuntary or recent, which may prompt a temporary reduction in support
Underemployment or unreported income, where a parent is intentionally earning less than they could or hiding earnings to reduce support obligations

In all these cases, the court will assess whether a deviation is justified, and if so, how to structure the order to ensure the child’s needs are fully met without unfairly burdening either parent. Evidence such as pay stubs, tax returns, affidavits, or expert testimony may be required to support a deviation request.

How Illinois courts enforce child support

Entry of support order

Once support is calculated and agreed upon, or ordered by the court, it becomes enforceable by law. A support order is issued and typically managed through Illinois’ Division of Child Support Services (DCSS).

Penalties for non-payment

Support is not optional. Even if the parent is unemployed or underemployed, they may still be imputed an income level based on past earnings or earning potential.

Failure to pay child support in Illinois can result in:

Wage garnishment
Seizure of tax refunds
Suspension of driver’s license or professional license
Civil contempt or even jail time for chronic non-compliance

When to update a support order

Child support orders are not permanent fixtures cast in iron and stone for years. Just like relationships and financial situations can change, so can child support obligations. Each parent has a right to request a review if there has been a substantial shift, like a job loss or promotion, a change in parenting time, or the child’s relocation. Request this review sooner rather than later! We’ve had scores of baby daddies coming ot us, regretting and lamenting as to why they didn’t file the paperwork when they received their job termination notice months earlier. To initiate this process, a parent must file a formal petition with the court, and both parties will be required to submit updated financial documentation.

Why it’s important to get professional help

Although Illinois child support calculations follow a pretty structured formula, we are dealing with human beings here, and thus the complexity of the cases is never-ending. That’s why working with an experienced attorney is essential, as we understand the nuances and complexities of the law and help real people every day win their case, or in some cases, win their lives back. At Lowry & Ivory, we ensure your income is accurately reported, appropriate credits and deductions are secured, and any modifications or enforcement actions are handled strategically.