Illinois Child Support Calculator (2026)

How Illinois calculates child support

Since July 1, 2017, section 505 of the Illinois Marriage and Dissolution of Marriage Act has used an income shares model. The court determines each parent's monthly net income, adds them together, and finds the basic child support obligation for that combined figure and the number of children in the Schedule of Basic Obligations published by the Department of Healthcare and Family Services. Each parent is then responsible for the percentage of that obligation that matches their share of combined net income, and the parent without the majority of parenting time pays their share to the other.

HFS revises the schedule periodically; the current version took effect March 20, 2026. The schedule runs in $50 increments of combined net income. Above the top of the schedule the court decides the amount, using the highest schedule figure as a floor.

Net income and the standardized tax table

Gross income includes wages, bonuses, commissions, self-employment income, rental income, retirement and disability benefits, unemployment, and spousal maintenance received. Net income is gross income minus taxes. Illinois lets the court use either a standardized tax amount, taken from the HFS Standardized Net Income Conversion Table for a single taxpayer claiming the standard deduction, or an individualized amount based on the parent's actual tax situation. This calculator follows the standardized approach with the 2026 federal figures and the 4.95% Illinois rate.

Maintenance actually paid to the other parent is added to the recipient's income and subtracted from the payor's before the calculation.

Shared physical care

When each parent has the children for 146 or more overnights a year, section 505(a)(3.8) applies a different formula. The basic obligation is multiplied by 1.5, each parent's share of that figure is multiplied by the percentage of time the children spend with the other parent, and the two amounts are offset. The parent with the larger obligation pays the difference. Because the threshold is a cliff, a schedule that moves a parent from 145 to 146 overnights can change support substantially.

If each parent has primary care of at least one child, the split care rule in section 505(a)(3.9) computes an obligation for each household and offsets them.

Add-ons, health insurance and other children

The court adds reasonable childcare costs, the children's share of health insurance premiums, and extraordinary medical or educational expenses to the basic obligation and divides them by the same income percentages. The parent who pays a premium or childcare bill directly gets credit for it. Section 505 also provides a multi-family adjustment that reduces a parent's income for children from other relationships they support, which this estimate does not apply.

Low-income parents and deviations

A paying parent with net income at or below 75% of the federal poverty guideline owes a minimum of $40 per month per child, up to a cap set by statute, unless the court finds even that unjust. The guideline amount is presumed correct at every income level, but the court may deviate after considering the children's needs, the parents' resources, the standard of living the children would have enjoyed, and their physical and emotional health, with written findings.

Duration, college and modification

Support continues until the child turns 18, or 19 if the child is still in high school. Illinois is unusual in allowing courts to order either parent to contribute to college or trade school expenses under section 513, generally capped at in-state costs at the University of Illinois. Either parent can seek a modification on a substantial change in circumstances, and HFS reviews orders in its caseload every three years on request.