Child Support

How Illinois Child Support Is Calculated

Illinois generally uses an income-shares model under 750 ILCS 5/505. The court determines each parent’s monthly net income, combines those amounts, selects the applicable basic support obligation from the Illinois Department of Healthcare and Family Services schedule, and allocates that obligation between the parents according to their respective shares of combined net income.

The guidelines are presumed to produce the correct amount of support, but a court may deviate when applying them would be inequitable, unjust, or inappropriate. Relevant considerations can include the financial resources and needs of the child and parents, the standard of living the child would have enjoyed if the household had remained intact, and the child’s physical, emotional, and educational needs.

Parenting time and shared physical care under current law

Through December 31, 2026, Illinois generally uses the shared-physical-care calculation when each parent exercises at least 146 overnights per year with the child. In those cases, the basic child support obligation is multiplied by 1.5, each parent’s share is calculated, and the resulting obligations are adjusted for the percentage of time the child spends with the other parent and then offset.

Parenting time can materially affect child support, but there is no simple dollar-per-overnight rule. Parenting decisions should be based on the child’s best interests, and the support calculation follows the applicable statutory framework.

Important Illinois child support changes take effect January 1, 2027

Illinois has already enacted a significant change to the child support statute. Public Act 104-0733, formerly Senate Bill 3524, was approved by the Governor on July 31, 2026 and takes effect January 1, 2027. The law is therefore enacted, although its new rules are not yet effective.

Among the most important changes:

• The shared-care threshold drops from 146 to 110 overnights per year. The new law also permits 110 or more “overnight equivalents” when determined by the court as a deviation from the guidelines or by agreement of the parties. Overnight equivalents address significant periods of direct care that occur on separate days without an overnight stay.
• A graduated adjustment applies between 110 and 145 overnights or overnight equivalents. The statute increases that parent’s shared-care obligation by 10% at 110–114, 9% at 115–119, 8% at 120–124, 7% at 125–129, 6% at 130–134, 4% at 135–139, and 2% at 140–145. The adjusted shared-care obligation may not exceed the amount that would otherwise be ordered under the basic support calculation.
• The low-income minimum-support threshold changes. The rebuttable presumption for a $40-per-month, per-child minimum obligation, subject to the existing $120 monthly maximum across all of the obligor’s children, will apply when actual or imputed gross income is at or below 100% of the federal poverty guideline for a one-person household, rather than 75%.
• Income-disclosure requirements expand. Child support orders will require both parents to exchange income information annually. A parent must also report new employment or termination of employment to the other parent and the clerk of court within 10 days, with the required written income verification.

The January 1, 2027 change does not mean every existing child support order automatically changes on that date. Existing orders and potential modifications must be evaluated under the applicable order, the facts of the case, and the modification standards in Illinois law. Families negotiating parenting schedules or support now should nevertheless understand how the 2027 framework may affect future calculations.

Additional child-related expenses

The basic support amount is only part of the analysis. Depending on the case, a support order may also address health-insurance costs, unreimbursed medical expenses, reasonable child-care expenses, and other child-related costs authorized by Illinois law. The allocation of these expenses can significantly affect each parent’s actual monthly responsibility.

Income issues in complex child support cases

Determining net income can become difficult when a parent is self-employed, owns a closely held business, receives bonuses or commissions, has irregular compensation, controls business expenses, or is alleged to be voluntarily underemployed. Illinois law contains rules for determining and, in appropriate cases, imputing income. Complex cases often require careful review of tax returns, payroll records, business financial statements, bank records, and other evidence.

Modification, enforcement, and when current support ends

Child support may generally be modified upon a substantial change in circumstances, and modifications ordinarily affect installments accruing after proper notice of the request for modification. Support orders can also be enforced when payments are not made as required.

Current child support generally terminates upon emancipation. If a child is still attending high school after turning 18, current support generally continues until the earlier of high-school graduation or age 19. Unpaid arrearages do not disappear when current support ends. Illinois also has separate statutory provisions addressing contribution to post-secondary educational expenses and support for certain non-minor children with disabilities.

Child support calculations are highly fact-specific. A worksheet is useful, but the quality of the income information and the correct treatment of parenting time and additional expenses often determine whether the result is reliable.

Estimate Illinois child support

Use our Illinois Child Support Calculator for a preliminary estimate based on income, parenting time, maintenance, and selected child-related expenses.