Illinois uses an income shares model (since 2017) combining both parents’ net incomes. A basic support obligation is determined from a schedule based on combined income and number of children. Each parent pays a pro rata share. Shared parenting (146+ overnights) triggers a 1.5x multiplier on the basic obligation.
Calculate Your Child Support →$39 one-time · No account needed · Report by email in 5 minutes
Illinois calculates child support using the Income shares model established under 750 ILCS 5/505. This is a statutory formula that leaves limited room for judicial discretion on the base calculation amount, ensuring consistency and predictability for families across the state.
Basic obligation from schedule based on combined net income and number of children. Each parent's share = (parent net income / combined net income) x basic obligation. Shared parenting (146+ overnights): 1.5x multiplier applied.
The calculation begins with determining each parent's net disposable income, which includes virtually all sources of income minus taxes, mandatory payroll deductions, and certain hardship deductions. The court then applies the statutory formula using the time each parent has primary physical responsibility for the children and the applicable income allocation brackets.
Beyond the base formula amount, Illinoisrequires additional contributions for mandatory add-on expenses. These typically include childcare costs necessary for the custodial parent's employment or education, uninsured healthcare expenses for the children, and in some cases, educational and travel costs. These add-ons are split between parents in proportion to their respective incomes.
Primary statute: 750 ILCS 5/505
Both parents’ net incomes combined to determine the basic support obligation.
146+ overnight threshold = shared parenting with 1.5x basic obligation multiplier.
Approximate percentages of combined net: 1 child ~17.5%, 2 ~25%, 3 ~30%, 4 ~33.5%, 5+ ~36.5%.
Add-ons: childcare, health insurance, unreimbursed medical (>$100/year/child), extracurricular, educational expenses.
Net income: gross minus federal/state taxes, FICA, mandatory retirement, health insurance (self), prior support obligations.
Illinois switched from percentage-of-income to income shares model in 2017.
IL public pensions (IMRF, SURS, TRS) require QILDRO, not standard QDRO.
2025 reform (PA 103-967) updated income imputation criteria.
Answer a few questions about your income, custody, and children. Get your personalized estimate.
Residency Requirement
90 days (one of the shortest in the US)
Mandatory Waiting Period
No mandatory waiting period
No-Fault Ground
Irreconcilable differences only (pure no-fault since 2016)
State Income Tax
Flat 4.95%
Illinois uses the Income shares model under 750 ILCS 5/505. Illinois uses an income shares model (since 2017) combining both parents’ net incomes. A basic support obligation is determined from a schedule based on combined income and number of children. Each parent pays a pro rata share. Shared parenting (146+ overnights) triggers a 1.5x multiplier on the basic obligation.
Key factors include both parents' income, the number of children, custodial time share, mandatory add-on expenses (childcare, health insurance), and any applicable deductions. Both parents’ net incomes combined to determine the basic support obligation.
Yes. Either parent can request a modification if there has been a material change in circumstances, such as a significant change in income, custody arrangements, or the needs of the child. The court will recalculate support using the same statutory formula.
Basic obligation from schedule based on combined net income and number of children. Each parent's share = (parent net income / combined net income) x basic obligation. Shared parenting (146+ overnights): 1.5x multiplier applied.
Get a personalized child support calculation based on Illinois's actual statutory formula.
Start My Free IllinoisEstimate →This tool provides educational estimates based on Illinois family law and does not constitute legal advice. Child support calculations are approximations of the statutory formula and may differ from court-ordered amounts. Consult a licensed Illinois family law attorney before making decisions. Primary statute: 750 ILCS 5/505.