In 2017, the passage of Public Act 99-764 (HB 3982) fundamentally transformed child support obligations for Illinois parents. By amending the Illinois Marriage and Dissolution of Marriage Act (IMDMA), the state moved away from a simple flat-percentage model to a more comprehensive Income Shares Model.
Today, this model is the established standard in DuPage County and throughout Illinois. It ensures that child support awards are calculated based on the combined financial standing of both parents, reflecting the lifestyle the child would have enjoyed had the parents remained in a single household.
Child Support Estimator
Illinois Income Shares Model (Effective 2026)
• Standard (Under 146 nights): The parent with the majority of parenting time is typically the recipient. The other parent pays their proportional share of the child’s needs.
• Shared (146+ nights): When both parents have at least 40% of the year, the law assumes both homes have significant fixed costs. We apply a 1.5x multiplier to the support amount, then “offset” the obligations based on the actual time spent. The parent with the higher total debt pays the difference to the other.
This is an estimate based on statutory guidelines.
Disclaimer: This child support calculator is provided for informational purposes only and is intended to offer a general estimate based on current Illinois statutory guidelines. It does not constitute legal advice, nor does it create an attorney-client relationship between you and Dolci Weiland & Sendlak.
Child support determinations involve complex variables—including tax filing status, health insurance premiums, multi-family adjustments, and judicial discretion—that this tool may not fully account for. The actual amount ordered by a court in Illinois may deviate from this estimate based on the specific “best interest” factors or other elements of your case. For an accurate calculation and to discuss potential deviations or modifications, we recommend consulting with one of our experienced family law attorneys.
Modern Legal Terminology
As part of a total overhaul of the IMDMA, Illinois has moved away from the term “custody.” Under current law, the courts “Allocate Parental Responsibilities” (decision-making) and “Parenting Time” (physical schedule). While the term “custodial parent” is still occasionally used in a general sense to describe the parent with whom the child resides most often, the law now focuses on the specific number of overnights spent with each parent.
How the Income Shares Model Works
The Income Shares Model holds both parents accountable for the financial support of their children. The calculation is based on three primary factors:
- Basic Child Support Obligation: A combined value derived from the state-provided schedule. This schedule cross-references the combined net monthly income of both parents with the number of children.
- Proportional Contribution: The basic obligation is divided proportionally between the parents based on their individual contribution to the combined net income. For example, if one parent earns 60% of the total income, they are responsible for 60% of the basic obligation.
- Additional Expenses: Costs for childcare, health insurance premiums, extraordinary medical expenses, and extracurricular activities are added to the basic obligation and shared proportionally.
Example Calculation
If a household has a combined net income of $10,000, and Parent A contributes $6,000 (60%) while Parent B contributes $4,000 (40%), Parent A is responsible for 60% of the basic support amount determined by the Illinois schedule.
Shared Parenting (The 146-Night Rule)
In Illinois, “Shared Parenting” occurs when each parent spends at least 146 overnights (40%) with the child annually. When this threshold is met, the child support calculation changes significantly:
- The 1.5x Multiplier: The basic support obligation is multiplied by 1.5 to account for the duplicate expenses (housing, utilities, transportation) inherent in maintaining two full households for the child.
- The Offset Method: Each parent’s shared care obligation is calculated and then multiplied by the other parent’s percentage of parenting time. These two resulting figures are offset against each other, and the parent with the higher obligation pays the difference to the parent with the lower obligation.
Cases that do not meet the 146-overnight threshold are calculated using the standard formula, where the parent with less parenting time pays their proportional share to the other parent.
Historical Context: Pre-July 1, 2017
While the Income Shares Model is the current law, some legacy cases may still be governed by the old flat-percentage model if they have not been modified since June 2017. Under that old system, the obligor (non-custodial parent) paid a fixed percentage of their net income regardless of the other parent’s earnings:
- 1 Child: 20%
- 2 Children: 28%
- 3 Children: 32%
- 4 Children: 45%
- 5+ Children: 50%
Note: The change in law itself is not considered a “substantial change in circumstances” required to modify an old order. However, changes in income, employment, or the child’s needs may allow you to petition the court to update your support order to the current Income Shares Model.
Contact Top DuPage Child Support Lawyers
Navigating child support schedules, net income conversions, and shared parenting offsets requires precision and experience. At Dolci Weiland & Sendlak, we have over 26 years of experience in Illinois family law. We help parents in Oakbrook Terrace, Chicago, and the surrounding areas ensure that their child support orders are fair, accurate, and in the best interests of their children.
To speak with a dedicated child support lawyer about your case or a potential modification, contact us at (630) 261-9098.