Illinois Child Support Calculator

Illinois uses the income shares model under 750 ILCS 5/505, which combines both parents' monthly net incomes and looks up the base child support obligation on the state's Schedule of Basic Obligations. Each parent pays a proportional share based on their percentage of total combined income. The schedule is updated annually, with the most recent revision effective March 5, 2025.

Illinois starts with each parent's gross income from all sources — wages, salary, commissions, bonuses, interest, dividends, and retirement benefits. Gross income is then converted to net by deducting federal taxes, Illinois state income tax at 4.95%, Social Security (wage base $176,100 in 2025), Medicare, and mandatory retirement contributions. Means-tested benefits like TANF, SSI, and SNAP are excluded.

When each parent exercises 146 or more overnights per year, Illinois applies the shared parenting formula under 750 ILCS 5/505(a)(3.8), which multiplies the base obligation by 1.5 and then allocates each parent's share by income percentage. This shared-care adjustment reduces the net transfer payment between parents. Below 146 overnights, the standard income shares formula applies without the 1.5 multiplier.

Illinois allows child support modification under 750 ILCS 5/510 upon showing a substantial change in circumstances, such as job loss or significant income change. Modification is also available without proving substantial change if the current order differs by at least 20% (and no less than $10 per month) from what current guidelines would produce. Filing a modification petition does not pause existing enforcement proceedings.

Beyond the base obligation from the Schedule, Illinois courts add healthcare insurance premiums, work-related childcare costs, and extraordinary expenses as additional child-related expenditures divided proportionally between parents. Under 750 ILCS 5/513, courts may also allocate college expenses — including tuition capped at University of Illinois at Urbana-Champaign in-state rates, room, and board — between parents until the child turns 23.

Illinois sets a presumptive minimum of $40 per child per month for obligors earning at or below 75% of federal poverty guidelines, with a total cap of $120 per month across all children. The Schedule of Basic Obligations tops out at combined net income of $30,024.99 per month ($360,300 annually). Above that threshold, the court exercises discretion, but the obligation cannot be less than the schedule's highest listed amount.

Illinois child support generally continues until the child turns 18 under 750 ILCS 5/505. If the child is still attending high school at 18, support extends until graduation or age 19, whichever comes first. Courts may separately order college expense contributions under Section 513, which can continue until age 23 — or age 25 for good cause such as military service or illness.

Illinois enforces child support through contempt of court, which can result in up to 6 months of periodic imprisonment under 750 ILCS 5/505. Additional enforcement tools include wage garnishment, property liens that attach automatically to overdue support, driver's license suspension, and criminal prosecution under the Non-Support Punishment Act. Parents must also report new employment within 10 days — failure to report combined with 60+ days of nonpayment constitutes indirect criminal contempt.