How Illinois Calculates Child Support Under the Income Shares Model
Under current Illinois law (750 ILCS 5/505), the Income Shares Model calculates support by estimating what intact families at similar income levels typically spend on their children and dividing that amount proportionally between the parents.
Step 1: Determine Each Parent’s Net Income
Illinois uses a standardized definition of net income based on income minus taxes, mandatory deductions, and allowable adjustments.
Step 2: Combine Incomes
Both parents’ net incomes are added together to determine the combined monthly net income.
Step 3: Consult the Income Shares Schedule
The Illinois Department of Healthcare and Family Services provides a schedule showing the basic support amount for families based on combined income and the number of children.
Step 4: Allocate Support Proportionally
Each parent is assigned a percentage share of the basic support obligation based on their contribution to total household income.
Step 5: Adjust for Parenting Time
If each parent has at least 146 overnights per year (equivalent to 40% parenting time), the shared parenting calculation applies.
Each parent’s obligation is recalculated and then offset to see who owes support.
Step 6: Add Additional Child-Related Expenses
Courts may allocate additional expenses proportionally, such as:
- Health insurance and medical expenses
- Childcare and work-related care needs
- Educational costs
- Extracurricular activities
- Camps and summer care
- Therapeutic or developmental services
Example: How Child Support Might Be Calculated
To understand the Income Shares Model in action, consider this simplified example:
- Parent A net income: $6,000/month
- Parent B net income: $4,000/month
- Combined income: $10,000/month
- Income Shares Schedule amount for one child: $1,600/month
Parent A earns 60% of the combined income → pays 60% of $1,600
Parent B earns 40% → pays 40% of $1,600
If the parents share 50/50 parenting time, each parent’s calculated obligation would be offset against the other, resulting in a single, adjusted child support payment.
Actual calculations may vary depending on expenses, parenting time adjustments, and other financial considerations.
Shared Parenting and Parenting Time Adjustments
Illinois applies its shared-parenting formula when:
- Each parent has 146 or more overnights per year, and
- Parenting time is reasonably balanced between homes
Support may increase or decrease depending on:
- The number of overnights
- Each parent’s childcare responsibilities
- Work schedules
- Additional expenses (healthcare, school needs, etc.)
Shared parenting calculations are more complex than standard support orders, so professional guidance is often helpful.
How Additional Child Expenses Are Divided
The Income Shares Model allows the court to order parents to contribute to:
Healthcare & Insurance
Unreimbursed medical, dental, orthodontic, vision, and prescription expenses not covered by insurance.
Childcare Expenses
Work-related childcare costs, including after-school care and care needed during training or education.
School & Extracurricular Costs
Tuition, books, tutoring, sports, clubs, art or music programs, camps, and summer activities.
Special Needs or Extraordinary Expenses
Therapy, counseling, developmental services, and other child-specific needs.
Unless otherwise ordered, these costs are divided in proportion to each parent’s income share.
Can Child Support Be Modified?
Yes. Illinois allows modification when there is a substantial change in circumstances, such as:
- Significant change in income
- Change in parenting time
- Job loss or promotion
- New financial obligations
- Major shift in a child’s needs or expenses
Frequently Asked Questions
Yes. The Income Shares Model considers both parents’ net incomes.
Absolutely. When each parent has 146+ overnights, the shared-parenting formula applies.
Yes. These costs are added to the basic support obligation and divided proportionally.
Yes, through a modification request if circumstances change significantly.
No. The Percentage of Income Model ended in 2017.
Work With Experienced Child Support Attorneys
Understanding Illinois child support rules can be complicated, especially when parenting time or expenses are shared. The attorneys at Conniff & Keleher, LLC can help you:
- Calculate support accurately
- Understand your rights and obligations
- Review or modify an existing order
- Navigate complex shared parenting cases
Contact us today to schedule a consultation.