Figuring out child support in Illinois can feel overwhelming, especially when you’re already dealing with the emotional weight of a divorce or custody matter. The good news? Illinois uses a structured formula that, once you understand it, becomes much more predictable than you might expect.
Since 2017, Illinois has relied on the “Income Shares Model” to calculate child support. This approach considers both parents’ incomes and aims to provide children with the same proportion of financial resources they would have received if the family had stayed together. It’s a fairer system than the old percentage-of-income method, but it does come with its own complexities.
At O’Dekirk, Allred & Rhodes, LLC, we’ve guided countless families in Joliet and throughout Illinois through the child support process. We know the questions that keep parents up at night: What income counts? How does parenting time factor in? Can the amount ever change? In this guide, we’ll break down exactly how child support is calculated in Illinois and what you need to know to protect your family’s interests.
Understanding the Income Shares Model
Illinois abandoned its old “percentage of income” model back in 2017 in favor of the Income Shares Model, and for good reason. The previous system only looked at the non-custodial parent’s income, which often led to unfair outcomes. The Income Shares Model takes a more holistic approach.
Here’s how it works in practice: both parents’ net incomes are combined to determine the total household income available to support the child. Illinois then uses statutory guidelines, essentially a table based on economic data about what families typically spend on children, to determine the basic child support obligation.
For example, let’s say Parent A earns $60,000 annually and Parent B earns $40,000. The combined income is $100,000. If the statutory table indicates that parents earning $100,000 combined typically spend $18,000 per year on one child, that becomes the basic support obligation.
But we’re not done yet. Each parent’s share is calculated proportionally. Parent A earns 60% of the combined income, so they’re responsible for $10,800 of that obligation. Parent B covers the remaining 40%, or $7,200.
The parent who has less parenting time (often called the “non-residential parent”) typically pays their share directly to the other parent. This ensures that the child’s standard of living remains as consistent as possible, regardless of which home they’re in at any given time.
One thing we always tell our clients: the Income Shares Model isn’t just about math. It’s about ensuring children don’t bear the financial burden of their parents’ separation.
What Counts as Income for Child Support
When calculating child support, Illinois courts cast a pretty wide net when defining “income.” This isn’t limited to your regular paycheck, not by a long shot.
Income for child support purposes includes:
- Wages, salaries, and commissions
- Bonuses and overtime pay
- Self-employment income
- Social Security benefits
- Pension and retirement payments
- Unemployment and workers’ compensation
- Interest and dividend income
- Rental income
- Trust income
- Annuity payments
- Capital gains
Basically, if money is coming in, it’s likely going to be considered. Courts want to capture the full financial picture of what each parent actually has available.
That said, certain types of income are excluded. Public assistance benefits (like SNAP or TANF), child support received for other children, and income from overtime that’s not guaranteed typically won’t count toward the calculation.
Gross Income vs. Net Income
Here’s where things get a bit more technical, and where we see a lot of confusion among our clients.
Illinois uses net income for child support calculations, not gross income. The difference matters significantly. Gross income is everything you earn before any deductions. Net income is what remains after certain standardized deductions are applied.
These standardized deductions include:
- Federal and state income taxes (based on the appropriate filing status)
- Social Security and Medicare taxes (FICA)
- Mandatory retirement contributions required by your employer
- Union dues
- Health insurance premiums for the parent (not the children, that’s handled separately)
- Prior child support or maintenance obligations for other relationships
Notice what’s not on that list: 401(k) contributions, car payments, credit card debt, or voluntary deductions. Those don’t reduce your income for child support purposes.
We often work with clients who are surprised by their calculated net income. It’s usually higher than what they see on their take-home paycheck because the court’s standardized deductions differ from what your employer actually withholds.
How Parenting Time Affects Support Amounts
Here’s something that trips up a lot of parents: the amount of time you spend with your child directly impacts your child support calculation. Illinois law recognizes that when a child spends significant time with both parents, both parents are incurring direct expenses for that child’s care.
Illinois uses a threshold of 146 overnights per year (roughly 40% of the year) to determine whether a “shared parenting” adjustment applies. If the parent with less time has the child for fewer than 146 overnights, the standard calculation applies. But if that parent has the child for 146 nights or more, a different formula kicks in that can substantially reduce the support obligation.
Why? Because when you have your child nearly half the time, you’re already paying for their food, activities, utilities, and everyday needs directly. The shared parenting formula accounts for this by reducing the transfer payment between households.
Let’s put some numbers to this. Using our earlier example where Parent A would owe $10,800 annually under the standard calculation: if Parent A actually has the child 180 overnights per year, that obligation could drop significantly, sometimes by 30% or more, depending on the specific circumstances.
This is one area where we see a lot of negotiation during custody discussions. Parents understandably want to maximize their time with their children, and the financial implications of parenting time often add another layer to those conversations. Our role is to help clients understand how different parenting schedules might affect support while keeping the focus on what’s genuinely best for the child.
One important note: you can’t just claim extra overnights to reduce support. The parenting time must be formalized in your parenting plan and actually exercised. Courts will verify that the overnight schedule is being followed.
Additional Expenses Beyond Basic Support
The basic child support obligation covers ordinary expenses, food, clothing, shelter, and similar day-to-day costs. But raising a child involves plenty of expenses that fall outside that “ordinary” category, and Illinois law addresses these separately.
These additional expenses are typically divided between parents in proportion to their respective incomes (the same ratio used for basic support). Common additional expenses include:
- Healthcare costs not covered by insurance
- Childcare expenses related to work or education
- Educational expenses (including extracurricular activities in some cases)
- Transportation costs for parenting time exchanges
Healthcare and Childcare Costs
Healthcare deserves special attention because it’s often one of the largest additional expenses families face.
First, the court will order one parent, usually whoever can obtain coverage at a more reasonable cost, to maintain health insurance for the child. The premium cost for the child’s coverage is then factored into the support calculation or divided between parents.
But insurance doesn’t cover everything. Copays, deductibles, prescription costs, orthodontia, therapy, glasses, these out-of-pocket expenses add up quickly. Illinois requires parents to share these unreimbursed medical expenses proportionally. If Parent A earns 60% of the combined income, they’ll cover 60% of that $500 dental bill the insurance didn’t fully pay.
Childcare is handled similarly. When a parent needs childcare to work or attend school, that cost gets added to the basic support obligation and divided proportionally. We’re talking about daycare, after-school programs, summer camps during work hours, essentially, the care required so parents can maintain their income.
These expenses must be reasonable and necessary. A parent can’t unilaterally sign the child up for a $5,000 summer enrichment program and demand the other parent cover their share without prior agreement or court approval. We always advise clients to communicate about major expenses beforehand and, when possible, get agreements in writing.
Deviations From the Standard Calculation
The Income Shares Model provides a starting point, but Illinois courts recognize that every family is different. Sometimes, applying the standard formula would produce an outcome that’s unjust or inappropriate given the specific circumstances.
Courts can deviate from the calculated amount, either upward or downward, when the standard number wouldn’t adequately address the child’s needs or would be inequitable to one of the parents. Factors that might justify a deviation include:
Factors that might increase support:
- A child’s special needs requiring additional care or equipment
- Extraordinary educational expenses
- A significantly higher standard of living that the child enjoyed before the separation
- One parent’s attempt to hide income or understate earnings
Factors that might decrease support:
- The paying parent’s support of other dependents not covered by existing orders
- Extraordinary travel expenses for parenting time (common when parents live far apart)
- The child’s own income or assets
- A financial hardship that would make the standard amount genuinely unmanageable
Deviations aren’t granted lightly. The parent requesting the deviation carries the burden of proving why the standard calculation is inappropriate. Courts will examine the evidence carefully and must explain their reasoning if they order an amount different from the guidelines.
We’ve successfully argued for deviations in both directions for our clients. Sometimes a child’s medical needs genuinely require more support than the formula suggests. Other times, a parent’s unique circumstances, like substantial debt from the marriage or support of elderly family members, warrant a reduction. The key is presenting compelling evidence and a clear legal argument for why deviation serves the child’s best interests.
Modifying Child Support Orders
Child support orders aren’t carved in stone. Life changes, and Illinois law allows for modifications when circumstances shift significantly.
To modify a child support order, you generally need to demonstrate a “substantial change in circumstances” since the original order was entered. Common qualifying changes include:
- A significant increase or decrease in either parent’s income (job loss, promotion, career change)
- Changes in the child’s needs (new medical condition, educational requirements)
- Changes in parenting time (one parent now has the child substantially more or less)
- Changes in the cost of health insurance or childcare
- Incarceration of the paying parent
- Emancipation of a child in a multiple-child order
Illinois also has a built-in review mechanism. Either parent can request a review every three years, and if the recalculated amount differs from the current order by at least 20% (or $100 per month, whichever is less), modification is presumed appropriate.
Here’s what many parents don’t realize: modifications aren’t automatic, and they’re not retroactive. If your income drops dramatically, you can’t just stop paying the current amount. You must file a petition to modify and continue paying the existing order until the court rules otherwise. The modification typically takes effect from the date you filed, not from when your circumstances changed.
This is why we always urge clients to act quickly when their situation changes. Waiting six months to file while struggling to pay the current amount can result in significant arrears that you’ll still owe even after modification.
At O’Dekirk, Allred & Rhodes, LLC, we handle child support modifications regularly. Whether you’re seeking an increase because your ex received a substantial raise, or you need a reduction due to unforeseen hardship, we can help you navigate the modification process efficiently.
Conclusion
Understanding how child support is calculated in Illinois doesn’t eliminate the stress of going through the process, but it does help you know what to expect and how to advocate for your family’s interests.
The Income Shares Model aims for fairness by considering both parents’ financial contributions. Your actual obligation will depend on both incomes, the amount of parenting time each parent exercises, and additional expenses like healthcare and childcare. And while the guidelines provide structure, courts maintain flexibility to deviate when circumstances warrant and to modify orders when life changes.
If you’re facing a child support matter, whether you’re establishing an initial order, seeking modification, or dealing with a post-divorce dispute, having experienced legal counsel makes a real difference. Our family law attorneys at O’Dekirk, Allred & Rhodes, LLC have helped families throughout Joliet and the surrounding counties navigate these issues for years. We understand the local court system, we know the law inside and out, and we’re committed to helping you achieve the best possible outcome for your family.
Reach out to our team when you’re ready to discuss your situation. We’re here to help.