Illinois Child Support Calculator
Calculate child support using Illinois's Income Shares model
Based on 750 ILCS 5/505 guidelines
Based on 750 ILCS 5/505 guidelines
How Illinois Calculates Child Support
Illinois switched from a simple percentage-of-income model to the Income Shares model on July 1, 2017. This considers both parents' incomes for a fairer calculation.
Income Shares Calculation Steps
- Calculate each parent's net monthly income
- Add both net incomes together for combined net income
- Look up the basic child support obligation in the guidelines table
- Calculate each parent's percentage share of combined income
- Multiply the basic obligation by the non-custodial parent's percentage
- Add healthcare, childcare, and other expenses (split by income percentage)
Example: If both parents earn $5,000/month net ($10,000 combined) and have 2 children, the basic obligation might be around $1,800. If the non-custodial parent earns 60% of combined income, their share would be $1,080/month.
Illinois-Specific Rules
- Illinois switched from percentage-of-income to Income Shares in 2017
- Shared parenting adjustment applies at 146+ overnights
- Courts can deviate from guidelines for good cause
- Support typically ends at age 18 or high school graduation
- College support can be ordered (one of few states)
- Maintenance (alimony) and child support are calculated separately
Factors in Illinois Child Support
Both Parents' Net Income
Illinois uses the Income Shares model, combining both parents' net incomes to determine the basic support obligation.
Number of Children
The guideline table provides support amounts based on the number of children, with amounts increasing for each additional child.
Parenting Time Percentage
If the non-custodial parent has 146+ overnight stays per year, a shared parenting adjustment applies.
Healthcare Expenses
Health insurance premiums and unreimbursed medical expenses are added to the basic support obligation.
Childcare Costs
Work-related childcare expenses are added and divided between parents based on income.
Educational Expenses
Private school tuition and extracurricular activities may be added if appropriate for the family.
Shared Parenting Adjustment
When Does It Apply?
If the non-custodial parent has 146 or more overnight stays per year (40% or more parenting time), Illinois applies a shared parenting adjustment that reduces the basic child support obligation.
This adjustment recognizes that both parents are directly spending money on the children during their respective parenting time.
How It's Calculated
- Calculate each parent's share of the basic obligation
- Multiply each share by 1.5 for shared parenting
- Multiply each result by the other parent's time percentage
- The difference between the two amounts is the support owed
The higher-earning parent typically pays the difference to the lower-earning parent.
Calculate Your Illinois Child Support
Use our free calculator to estimate child support based on Illinois Income Shares guidelines. Splitifi can help you track payments, document expenses, and plan custody schedules.