Deviation from Child Support Guidelines in Illinois

The Guideline Is Presumptively Correct

Illinois child support starts with the Income Shares Model under 750 ILCS 5/505. You combine both parents' net incomes, look up the basic support obligation on the HFS schedule, and split it proportionally. That number is presumed to be the right amount. A judge can deviate from it — but only with a specific written finding that the guideline figure would be "unjust, inappropriate, or not in the best interests of the child."

This is a high bar. Courts don't deviate because one parent thinks the number is unfair. They deviate when the standard formula produces a result that doesn't match the child's actual circumstances.

Grounds That Justify a Deviation

The statute lists several factors a judge may consider. In practice, successful deviation requests cluster around a few scenarios:

Extraordinary medical or therapeutic needs. A child with a chronic condition requiring ongoing specialist care, therapy, or medical equipment that exceeds what the standard obligation covers. The key word is extraordinary — ordinary expenses covered by the basic obligation are not, by themselves, extraordinary; unreimbursed medical needs may be addressed separately as add-on expenses.

Extraordinary educational needs. A child with documented learning disabilities or other extraordinary educational needs may justify an amount above the guideline. Reasonable school expenses may also be ordered separately under the child-support statute.

Significant travel costs for parenting time. When parents live far enough apart that regular transportation for parenting exchanges becomes a substantial expense — think weekly flights or 200-mile round trips every other weekend — a deviation can account for those costs.

Vast income disparity affecting the child's standard of living. If one parent earns $400,000 annually and the other earns $35,000, the standard formula may not produce an amount that allows the child to maintain a comparable lifestyle in both homes. Courts can deviate upward to bridge that gap.

Income that exceeds the HFS schedule maximum. The schedule has an upper combined income limit. For parents whose combined income exceeds that ceiling, the court determines support using its discretion rather than a mechanical table lookup.

How to Request a Deviation

Either parent can request a deviation — upward or downward. The process:

1. Calculate the standard guideline amount first. You need the baseline number before arguing that it should be different.
2. File a written motion explaining the specific reason the guideline is unjust or inappropriate for your child's circumstances.
3. Attach supporting evidence — medical bills, school tuition invoices, travel receipts, or income documentation.
4. Be prepared for a hearing where the judge evaluates both parents' positions.

The judge must enter written findings specifying the reasons for the deviation and the presumed guideline amount without a deviation. This requirement protects both parents — it creates an appellate record and prevents arbitrary adjustments.

Downward Deviations

Deviations don't only go up. A parent can request a reduction below the guideline when:

• They're supporting other children not covered by this order (though this is partially handled through deductions in the standard calculation)
• The child has independent income or assets, such as a trust fund
• The receiving parent has substantially higher income and the standard obligation would create an unnecessary wealth transfer rather than serve the child's needs

Downward deviations face skepticism. Courts default to the position that more support benefits the child, so the evidence for a reduction needs to be compelling.

Deviations vs. Modifications

A deviation is decided at the time the original support order is entered (or at a modification hearing). It's different from a modification, which requires a substantial change in circumstances after the order is already in place. If your income drops substantially after the order, you'd seek a modification under 750 ILCS 5/510 based on a substantial change in circumstances — not argue for a deviation from the existing order. The statute's separate 20%-and-$10 guideline-comparison route is limited to cases in which a party receives HFS child-support enforcement services and at least 36 months have elapsed since the order was entered or last modified.

The distinction matters because deviation arguments are usually made during the initial support negotiation. If you're drafting your parenting plan and calculating support, this is the time to identify whether a deviation applies to your situation.

Building Your Case

Deviation requests succeed when the evidence is specific and documented. Vague claims about "high expenses" won't work. What does:

• Itemized medical bills showing out-of-pocket costs over the past 12 months
• Written documentation from specialists about expected ongoing treatment costs
• School enrollment agreements and tuition receipts
• A log of transportation expenses for parenting time exchanges over 6+ months
• Both parents' complete financial affidavits showing the income disparity

Our Illinois Child Custody & Parenting Plan Guide walks through the standard child support calculation step by step and includes a worksheet for documenting add-on expenses — which gives you the foundation to identify whether a deviation argument is viable before you bring it to a judge or mediator.

See more Illinois guides →