Illinois Child Support Calculator

Calculate Illinois child support obligations under the 750 ILCS 5/505 Income Shares Model. Computes combined net income, basic support schedules, shared physical care (146+ overnights), and add-on adjustments.

Case Parameters

750 ILCS 5/505
Monthly income after standard tax deductions
$
Monthly income after standard tax deductions
$
146+ days (40%) triggers shared care
days
Mandatory Add-Ons Paid by Parent 1
Paid directly for child
$
Employment related
$
Estimated Monthly Child Support Transfer
$769/ month
Obligation DirectionParent 1 → Parent 2

Combined Net

$8,700

63% / 37% split

Basic Schedule Need

$1,479

HFS guideline table

Physical Care Mode

Standard Care

80 overnights/yr

Illinois Support Breakdown Matrix

2 Children
Combined Net Monthly Income:$8,700
Basic Child Obligation (Combined):$1,479
Parent 1 Pro-Rata Share (63.2%):$935
Mandatory Healthcare & Childcare Add-Ons:+$284
Final Monthly Transfer:$769 / mo

Illinois Child Support utilizes net income rather than gross income.

When either parent exercises at least 146 overnights (40% of the year), the shared physical care formula applies a 1.5 multiplier to account for duplicated household expenditures.

How Illinois Child Support Is Calculated

Illinois child support follows the Income Shares Model codified in 750 ILCS 5/505. Under this statute, the basic financial obligation is calculated from the Illinois Department of Healthcare and Family Services (HFS) schedule and apportioned between parents.

1. Illinois Income Shares Basic Need Formula
Basic Support Obligation=HFS Schedule Table(Combined Net Income, Children)
2. Individual Parent Monthly Transfer Obligation
Monthly Transfer=(Basic Need + Total Add-Ons) ×
Parent Net IncomeCombined Net Income
− Direct Expenses Paid
Step-by-Step Calculation Breakdown ($5,500 vs $3,200 Monthly Net, 2 Children)
Step 1: Determine Combined Net Income & Income Share Proportions
• Parent 1 Net: $5,500/mo | Parent 2 Net: $3,200/mo
• Combined Monthly Net: $8,700 / month
• Parent 1 Income Share: $5,500 ÷ $8,700 = 63.2%
• Parent 2 Income Share: $3,200 ÷ $8,700 = 36.8%
Step 2: Lookup Illinois HFS Basic Schedule Obligation
• Basic Schedule Obligation (2 Children on $8,700): $1,479 / month
• Parent 1 Base Pro-Rata Share (63.2%): $1,479 × 63.2% = $935 / mo
Step 3: Apportion Add-Ons & Calculate Net Monthly Transfer
• Health Insurance ($150) + Childcare ($300) = $450 total add-on
• Parent 1 Add-On Obligation (63.2%): +$284 / month
• Less Direct Payments by Parent 1: -$450
Estimated Net Monthly Child Support Transfer: $769 / month

Illinois HFS Obligation Schedule Reference (Representative Net Incomes)

Combined Net Income1 Child2 Children3 Children4 Children
$4,000 / mo$480$760$880$1,000
$7,000 / mo$700$1,190$1,400$1,610
$10,000 / mo$900$1,500$1,800$2,100
$15,000 / mo$1,200$2,100$2,550$3,000

Frequently Asked Questions

How does the Illinois Income Shares Model work?
Under 750 ILCS 5/505, Illinois calculates child support using the Income Shares Model. Support is based on what parents would spend on children if living together, divided proportionally according to each parent's share of combined monthly net income.
How does parenting time (shared physical care) affect Illinois support?
When a non-custodial parent exercises at least 146 overnights per year (40% time-share), Illinois applies the Shared Physical Care formula. The basic obligation is multiplied by 1.5×, and each parent's obligation is offset based on time spent with each child.
What counts as gross income under Illinois family law?
Illinois defines gross income broadly to include wages, salaries, overtime, bonuses, self-employment income, rental income, pensions, and capital gains, minus statutory deductions (taxes, mandatory union dues, prior support orders).
How are healthcare and childcare expenses split in Illinois?
Health insurance premiums, extraordinary medical expenses (exceeding $250/yr), and employment-related childcare costs are mandatory add-ons apportioned pro-rata based on each parent's net income percentage.
When can an Illinois child support order be modified?
Illinois allows modification upon showing a substantial change in circumstances (e.g., 20%+ change in income or parenting time), or automatically every 3 years upon petition to the Illinois Department of Healthcare and Family Services (HFS).

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