Illinois calculates child support using the Income Shares Model. This approach aims to replicate the amount parents would spend on their children if living together, based on combined net income and the number of children.
The Illinois Department of Healthcare and Family Services (HFS) publishes an official schedule of basic obligations, updated periodically (most recent adjustments effective around March 2025) and courts presume the guidelines apply, but certainly can deviate from the standard calculation depending on the unique circumstances of a case.
Step-by-Step Calculation to Determine Child Support Obligation
- Start by determining net income: Take the gross income for each parent from all sources (excluding certain public benefits). Subtract standardized/actual taxes and subtract adjustments such as support paid for other children or spousal maintenance.
- Combine the net incomes: Add both parents’ monthly net incomes.
- Find the basic obligation: Reference the HFS Income Shares Schedule for the amount based on combined income and number of children.
- Allocate shares: Each parent contributes proportionally to their percentage of combined income. The parent with primary parenting time is presumed to spend their share directly.
- Adjust for parenting time: If each parent has 146+ overnights per year (shared physical care), multiply the basic obligation by 1.5, then offset based on time spent with the other parent.
- Add extras: Include prorated child health insurance premiums, childcare costs, and uninsured medical expenses. These are typically added to the total and split by income percentages.
The obligor parent pays the difference to the recipient parent. Use the free official HFS Child Support Estimator for quick estimates. Consult an experienced child support attorney for more information and to discuss your concerns regarding child support and custody arrangements.
Example Calculation of Illinois Income Shares Model
In a scenario where there are two parents with one child, the following calculation may apply:
- Parent A (primary caregiver): $4,000 monthly net income (40% share)
- Parent B: $6,000 monthly net income (60% share)
- Combined net income: $10,000
From the current schedule, the basic obligation is approximately $1,658 per month.
- Parent B’s share: 60% of $1,658 ≈ $995.
- No shared parenting or extras assumed → Parent B pays $995/month to Parent A.
If Parent B also pays $150/month for the child’s health insurance, add that cost, prorate, and adjust the payment accordingly (e.g., Parent A’s 40% share of the premium would reduce Parent B’s obligation slightly). Shared parenting (146+ overnights) or added childcare could change the final amount significantly.
Extraordinary Factors That May Influence or Allow Deviation by the Court
The Court may deviate from the standard calculation if strict application is not in the child’s best interests. Key extraordinary factors may include:
- Extraordinary medical expenditures
- Additional costs for a child with special needs
- A child’s educational needs
- The family’s prior standard of living, or the financial resources/needs of the child and parents
- Imputed income if a parent is voluntarily underemployed
Judges consider the child’s overall best interests and may order deviations when evidence shows the guideline amount is inappropriate. It is important to work with an experienced child support attorney to ensure that child support is fair to both parties and prioritizes the best interests of the child.
Modification of Child Support Orders
Child support orders can be modified for substantial changes in income, custody, or needs. A child support modification attorney can help if you need to reduce child support due to a loss or reduction in income or other issue, such as medical needs, that has changed the obligor’s financial situation significantly. Conversely, if you are seeking additional child support due to a child’s changing financial need or because the recipient believes the obligor has had a significant increase in income since the original order, it may be worthwhile to talk to a child support modification attorney.
Contact an Experienced Child Support Attorney for Help
Divorcing parents should work with an experienced child support attorney as individual circumstances can make a difference in the child support determination. When you have questions regarding Illinois child support, contact the Libertyville Family Law Office of Ronald L. Bell & Associates for answers.
