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Children & Parenting
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Child Support
Child Support Attorney in Illinois
As an Illinois child support attorney, I know that the state uses an income shares model — meaning both parents' incomes factor into the calculation, not just the non-custodial parent's.
Both parents' incomes matter —
not just one.
Illinois adopted the income shares model for child support in 2017, replacing the older percentage-of-income approach. The fundamental shift: both parents' net incomes now factor into the calculation. The model is based on the principle that children should receive the same proportion of parental income they would have received if the family had stayed intact.
The guidelines produce a base support obligation — but they are a starting point, not an absolute. Courts can deviate from the guidelines when the standard result would be inappropriate given the specific circumstances of the case. Add-on expenses — health insurance, child care, and extraordinary medical costs — are allocated separately on top of the base obligation, proportionally based on each parent's share of combined income.
How income is calculated and documented matters enormously. Whether a parent's income is properly reflected — including self-employment income, bonuses, overtime, and imputed income for a voluntarily underemployed parent — can change the support obligation significantly. We analyze income carefully and advocate for accurate calculations from both sides.
Child support in Illinois is governed by 750 ILCS 5/505 and the Illinois Schedule of Basic Obligations, which provides the guideline amounts based on combined net income and number of children. Courts are required to follow the guidelines unless a deviation is justified — and any deviation must be documented with specific findings about why the guideline amount would be inappropriate or unjust.
The income shares model — step by step.
The income shares calculation follows a defined sequence. Understanding each step helps you see where the critical decisions are — and where disputes about the calculation typically arise.
Net Monthly Income
Net Monthly Income
Both parents' net incomes added together
Guideline amount from the Illinois schedule
Health insurance · Child care · Extraordinary medical
Base obligation + proportional share of add-ons
Add-on expenses — what they are and how they're shared.
The base child support obligation covers the child's basic living expenses. Add-on expenses are specific costs that are allocated separately — on top of the base obligation — proportionally based on each parent's share of combined net income. Understanding what qualifies as an add-on, and how each expense is documented and allocated, is a significant part of every child support determination.
How proportional allocation works
If Parent A earns 60% of the combined net income and Parent B earns 40%, add-on expenses are allocated 60/40. This means the parent with higher income pays a larger share of add-ons — regardless of which parent incurred the expense.
Both parents are required to provide documentation of add-on expenses. Disputes about what qualifies as an add-on, whether an expense was necessary, and whether proper documentation was provided are common sources of post-decree conflict.
The cost of the child's health insurance coverage — specifically the premium attributable to the child — is an add-on expense allocated proportionally. Courts determine which parent's plan provides appropriate coverage and allocate the cost accordingly. Disputes about which plan to use and what the child-specific premium cost is are common.
Reasonable child care expenses necessary for a parent to work or attend school are allocated proportionally as an add-on. This includes daycare, after-school programs, and summer care. Courts look at whether the expense is reasonable and necessary — not the most expensive option available, but appropriate for the family's circumstances.
Medical, dental, and optical expenses that exceed a specified threshold — typically amounts not covered by insurance — are allocated proportionally as extraordinary medical expenses. Both parents typically share uninsured medical costs proportionally, and most parenting orders require advance notice and consent for non-emergency extraordinary expenses above a certain dollar amount.
Courts may also allocate other expenses proportionally — educational costs, extracurricular activity fees, and similar items — either by agreement of the parties or by court order when appropriate. These are not automatic add-ons but can be included in the support order when both parties agree or when the court finds allocation is in the child's best interest.
Three situations that can change your support obligation.
Child support is not permanent. Illinois law allows modification when circumstances change — but not every change qualifies, and the direction of modification depends entirely on the nature of the change.
Three-Year Review or 20% Change
Illinois law presumes a substantial change in circumstances — and therefore grounds for modification — when either three years have passed since the last order was entered or the guideline calculation would change by more than 20% from the existing order. This is one of the clearest modification thresholds in Illinois family law. Either condition alone is sufficient to support a modification petition.
Significant Income Increase or Decrease
A meaningful change in either parent's income — job loss, significant raise, career change, disability, retirement — can support a modification petition outside of the three-year window. The change must be substantial and, in cases of voluntary income reduction, courts will scrutinize whether the reduction was in good faith or designed to reduce support. We analyze income changes carefully on both sides.
Changes in the Child's Needs or Living Situation
A significant change in the child's needs — a new medical condition, change in educational expenses, change in child care costs — or a material change in the parenting time schedule can also support a modification. When a parenting time arrangement changes substantially, the support calculation should be revisited to reflect the new reality of how the child's time is allocated between the parents.
What clients ask about child support in Illinois.
These are the questions prospective clients most often raise before their first consultation. We've answered them honestly — because informed clients make better decisions, and that's better for everyone.
What counts as income for child support purposes in Illinois?
Can the court deviate from the guideline support amount?
What happens if a parent doesn't pay court-ordered support?
Does parenting time affect how much support is paid?
When does child support end in Illinois?
Can we agree to a support amount different from the guidelines?
"How income is calculated and documented can change the support obligation significantly."
Child Support Attorney
Serving Chicagoland
O'Brien Family Law handles child support matters — initial calculations, modifications, and enforcement — throughout Cook, DuPage, Kane, Kendall, Lake, and Will County. We appear regularly in the circuit courts of each county and understand how local judges approach support disputes.
Whether your matter is contested or agreed, simple or complex, we're positioned to represent you effectively from the first consultation through the final order.
Accurate support starts with accurate income.
Whether you're seeking support, defending against an excessive calculation, or pursuing a modification — the first conversation is free, confidential, and carries no obligation.
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