Child Support in Illinois: Income Shares, the 146-Overnight Rule and the 2027 Changes

Illinois uses an income shares model for child support, set out in section 505 of the Illinois Marriage and Dissolution of Marriage Act and the schedule published by the Department of Healthcare and Family Services (HFS). The idea is that a child should get the share of parental income the child would have received if the parents lived together, divided between the parents by their incomes.

Big changes take effect January 1, 2027; they're explained at the end of this page.

How the calculation works

1. Find each parent's net income. Start with gross income from all sources, then subtract taxes, usually using a standardized tax amount from HFS tables (an individualized amount can be used by agreement or after a hearing).
2. Add the two net incomes to get combined monthly net income.
3. Look up the basic obligation for that combined income and the number of children on the HFS schedule.
4. Split it by income. Each parent is responsible for his or her percentage of combined net income; the parent with less parenting time pays his or her share to the other.
5. Adjust for shared parenting time, health insurance, child care and other expenses.

For an estimate, use the state's official child support estimator. The current schedule took effect March 20, 2026, and now runs to $27,374.99 of combined monthly net income (previously $26,724.99). Above the top of the schedule, the court decides support in its discretion, but not less than the amount at the highest level of the schedule.

Imputed income

If a parent is voluntarily unemployed or underemployed, the court can base support on the income he or she could earn. Since January 1, 2025, it must look at the parent's actual circumstances (assets, residence, work history, job skills, education, literacy, age, health, criminal record and other barriers to work, and the local job market), and it can impute income "only upon conducting an evidentiary hearing or by agreement," with specific written findings. Section 505 also states that "Incarceration shall not be considered voluntary unemployment."

Low incomes

There's a presumptive minimum order of $40 per month per child, up to $120 a month in total, for a parent whose actual or imputed gross income is at or below 75% of the federal poverty guideline for one person (§ 505(a)(3.3a)). A zero-dollar order is presumed for a parent with no gross income who receives only means-tested assistance, or who is incarcerated, institutionalized or medically disabled (§ 505(a)(3.3b)).

Shared parenting: the 146-overnight rule

Through December 31, 2026, Illinois uses a special formula when both parents have substantial time. 750 ILCS 5/505(a)(3.8):

(3.8) Shared physical care. 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. The court shall determine each parent's share of the shared care child support obligation based on the parent's percentage share of combined net income.

Each parent's share is then multiplied by the percentage of time the child spends with the other parent, and the two amounts are offset. Equal time doesn't automatically mean no support: the higher earner usually still pays.

Add-ons

• Health insurance. The court allocates the cost of covering the children. A reasonable premium generally can't exceed 5% of the providing parent's gross income.
• Child care. The court may order the parents to share reasonable child care costs needed for work, education or a job search, in proportion to their incomes.
• School and extracurricular expenses. The court may order contributions to reasonable school and extracurricular costs; this is discretionary.

How long support lasts

Support generally continues until the child turns 18, or, for a child still in high school, until graduation or age 19, whichever comes first.

College expenses

Illinois is one of the states that let courts order divorced parents to help pay for college (750 ILCS 5/513). The expenses must generally be incurred before the student's 23rd birthday (up to 25 for good cause), and the statute caps them at what the University of Illinois at Urbana-Champaign charges: in-state tuition and fees, and a double room with a standard meal plan, for the same academic year. The court can require the student to fill out the FAFSA, and a college savings account counts as a resource. Support ends if the student doesn't keep a cumulative "C" average, earns a bachelor's degree, or marries.

Changing a support order

A parent can ask the court to modify support after a substantial change in circumstances (§ 510). Don't wait: a judgment may be modified "only as to installments accruing subsequent to due notice by the moving party of the filing of the motion for modification."

What changes on January 1, 2027

Public Act 104-0733 rewrites parts of § 505 effective January 1, 2027:

• Shared care starts at 110 overnights a year (or 110 "overnight equivalents"), down from 146, with a graduated increase for the parent with fewer than 146 overnights. The adjusted amount can't exceed the basic guideline amount.
• The low-income minimum applies to parents at or below 100% of the federal poverty guideline, up from 75%.
• Parents must exchange income information every year.
• Incarceration of more than 180 days gets its own modification process.

The change doesn't modify existing orders by itself: a parent has to ask, and the court must find a substantial change in circumstances.

Where these sections live

• 750 ILCS 5/505 — Child support
• 750 ILCS 5/513 — Educational expenses
• 750 ILCS 5/510 — Modification
• HFS: income shares and the schedule
• HFS: child support estimator