How it works · official guideline
How child support is calculated in Illinois
Illinois computes support from both parents' monthly net incomes: they are added together, the basic obligation is read from the Department of Healthcare and Family Services schedule for that combined income and number of children, and each parent’s share follows their percentage of the combined income. When each parent has at least 146 overnights a year, a 1.5 shared-care multiplier and offset apply.[1]
Key facts: child support in Illinois
| Guideline model | Income shares[1] |
|---|---|
| Income counted | Net income (gross minus standardized or individualized taxes)[1] |
| Shared parenting time | 146 or more overnights each: basic obligation × 1.5, cross-multiplied and offset[1] |
| Minimum order | $40 per month per child (max $120) for very low incomes[1] |
| Official calculator | Illinois Child Support Estimator (Department of Healthcare and Family Services) |
| Guideline last checked | October 26, 2026 |
Illinois’s model
Income shares
Income shares: combined monthly net income, then HFS schedule of basic child support obligations, split by each parent’s percentage share.
Official calculator · Illinois Department of Healthcare and Family Services, Division of Child Support Services
Illinois Child Support Estimator (Department of Healthcare and Family Services)Link checked October 26, 2026
Why no calculator here? We publish a calculator only after it reproduces the state’s official numbers exactly. We haven’t matched Illinois’s yet, so use the official calculator for a number.
From the official text
The rules behind Illinois’s numbers
The guideline is 750 ILCS 5/505(a)(1.5). Open each rule to read the exact words.
- Income counted
Net income (gross minus standardized or individualized taxes)
Net income is gross income minus a standardized tax amount (from the HFS conversion table) or, when its conditions are met, an individualized tax amount, and minus listed adjustments.[1]
Official text · 750 ILCS 5/505(a)(3)(B)
“As used in this Section, "net income" means gross income minus either the standardized tax amount calculated pursuant to subparagraph (C) of this paragraph (3) or the individualized tax amount calculated pursuant to subparagraph (D) of this paragraph (3), and minus any adjustments pursuant to subparagraph (F) of this paragraph (3).”
- Shared parenting time
146 or more overnights each: basic obligation × 1.5, cross-multiplied and offset
If each parent has the child at least 146 overnights a year, the basic obligation is multiplied by 1.5, split by income share, multiplied by the other parent’s time share, and the two amounts are offset.[1]
Official text · 750 ILCS 5/505(a)(3.8)
“If each parent exercises 146 or more overnights per year with the child, the basic child support obligation is multiplied by 1.5 to calculate the shared care child support obligation.”
- Minimum order
$40 per month per child (max $120) for very low incomes
For a payer with gross income at or below 75% of the federal poverty guideline for one person, a minimum order of $40 a month per child is presumed, capped at $120 in total.[1]
Official text · 750 ILCS 5/505(a)(3.3a)
“There is a rebuttable presumption that a minimum child support obligation of $40 per month, per child, will be entered for an obligor who has actual or imputed gross income at or less than 75% of the most recent United States Department of Health and Human Services Federal Poverty Guidelines for a family of one person, with a maximum total child support obligation for that obligor of $120 per month to be divided equally among all of the obligor's children.”
- Top of the guidelines
Above the schedule’s top: court discretion, at least the top amount
When combined net income exceeds the top of the schedule, the court has discretion but the basic obligation may not be less than the highest schedule level.[1]
Official text · 750 ILCS 5/505(a)(3.5)
“A court may use its discretion to determine child support if the combined adjusted net income of the parties exceeds the highest level of the schedule of basic child support obligation, except that the basic child support obligation shall not be less than the highest level of combined net income set forth in the schedule of basic child support obligation.”
Guideline: 750 ILCS 5/505(a)(1.5) (Illinois General Assembly), checked October 26, 2026.
Estimate and general information only — not legal advice. MediationList is a directory, not a law firm, and doesn’t endorse any mediator. Guidelines change; confirm with the official calculator (sources checked October 26, 2026). See also divorce laws in Illinois and child support in every state.
Sources
Illinois’s child support guideline, rules and official tools, read on the official sites, with the date we checked each.