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State Guide · Illinois
Child Support in Illinois: How It's Calculated, Modified & Enforced
A plain-English guide to Illinois child support — the guideline model, how the number is computed, the modification and enforcement process, and where to find the official worksheet.
Direct answer
Net income. Gross income is reduced by a standardized tax amount (HFS table) or the parent\'s actual individualized taxes to reach net income.
Illinois uses the Income Shares model under 750 ILCS 5/505 (effective July 2017, replacing the old percentage-of-obligor model). It starts from each parent's gross income, subtracts a standardized or individualized tax amount to reach net income, then applies the Schedule of Basic Child Support Obligations. The Division of Child Support Services (HFS) updates the schedule and gross-to-net conversion table annually. Health insurance and childcare add-ons are allocated; deviations require written findings stating the guideline amount.
Open the Illinois child support calculator to see your own number under the current guideline: Illinois calculator.
How a support order is established in Illinois
Apply through the HFS Division of Child Support Services or file in court (dissolution, parentage, or support action).
Establish parentage if unmarried (voluntary acknowledgment or court testing).
Both parents provide income data; use the free Illinois Child Support Estimator / Income Shares worksheet (HFS).
The court enters an order based on the guideline; deviations beyond the worksheet require written findings.
Support is paid via income withholding; HFS enforces.
To modify, file a motion showing a substantial change in circumstances; the worksheet is recalculated.
Worked examples
Illustrative example — net-income split (one child) — Parent A net $1,000/mo; Parent B net $500/mo; combined net $1,500/mo; one child. From the Illinois schedule, the basic obligation for $1,500 combined net and one child ≈ $325 (illustrative schedule figure from HFS documentation). Parent A = 67% → 0.67 × $325 ≈ $217/mo, plus their share of add-ons (health insurance, childcare). Illinois allocates the basic obligation by each parent\'s percentage of combined net income.
Illustrative example — standardized tax conversion — Parent with higher gross income but several dependents. Illinois converts gross to net using either the HFS standardized tax table or the parent\'s actual individualized tax amount; the chosen net figure drives the schedule lookup. Because Illinois uses net income, the gross-to-net conversion (standardized table or actual taxes) materially affects the result.
Modifying or enforcing an order
Orders in Illinois can be modified when there is a substantial change in income, custody, or circumstances. Use the modification eligibility check and the cross-state comparison tool to see how a move would change the outcome. Enforcement runs through the state agency and can include income withholding and contempt proceedings.
Official sources
Illinois HFS — Child Support Services — https://hfs.illinois.gov/childsupport
Illinois General Assembly — 750 ILCS 5/505 — https://ilga.gov
Is Illinois gross or net income?
Net income. Gross income is reduced by a standardized tax amount (HFS table) or the parent\'s actual individualized taxes to reach net income.
What changed in 2017?
Illinois replaced its old flat-percentage-of-obligor model with the Income Shares model under 750 ILCS 5/505.
Can the court deviate from the guideline?
Yes, with written findings stating the amount the guidelines would have required and the reason for the variance.
When does support end?
At age 18, or 19 if the child is still in high school.
How is the schedule updated?
HFS revises the Schedule of Basic Obligations and the gross-to-net conversion table annually for current economic data.
What if a parent is voluntarily unemployed?
The court may impute income based on work history, skills, and the local job market; incarceration is not treated as voluntary unemployment.
Illinois child support calculator
Estimate for Illinois
Illinois uses the Income Shares model.
Enter the paying parent’s net (after-tax/deductions) monthly income.
Illinois Child Support Worksheet — Planning Estimate
Generated September 22, 2026 · Model: Income Shares · Income basis: net · Statute: 750 ILCS 5/505
This is an informal planning estimate, not a court worksheet and not legal advice. Confirm the current guideline with the state child-support agency or a licensed family-law attorney.
Estimated monthly support$1,306.11per month
Official schedule: Illinois HFS, '2026 Addendum to the Illinois Schedule of Basic Obligations and Standardized Net Income Table' (submitted to IL Dept. of Healthcare and Family Services, Division of Child Support Services, Mar. 13, 2026). (2026)
Annual estimate$15,673.32
Effective rate26.1%
MethodIncome Shares: combined income → official Illinois schedule → split by income share (+ add-ons, parenting-time credit)
View calculation breakdown
Combined parental income
$9,000
Total basic obligation (schedule)
$2,351
Obligor income share
55.6%
Obligor basic obligation
$1,306
Estimated monthly support
$1,306
How the basic obligation splits between parents
56%
44%
Paying parent: $1,306 Other parent: $1,045
Each parent pays their proportional share of the combined basic obligation.
Estimated monthly support by number of children
At the incomes you entered, for 2 children.
This article is general education, not legal or tax advice. For your exact number, open your state calculator.
Not legal or financial advice. This estimate follows the state’s statutory guideline formula but cannot capture every factor a court considers (health insurance, childcare, prior orders, deviations, imputed income).
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