## How is child support calculated in Illinois? Illinois uses the **Income Shares model**. Here's how it works. Both parents' incomes are combined to estimate what they would have spent on the child as an intact family. That total is then divided between them in proportion to their incomes. The parent who has the child less time pays their share of the total to the other parent. This is the most common model in the United States — used by 40+ states. **Worth knowing about Illinois:** Illinois switched from percentage to income shares in 2017. ## What goes into the calculation Most states' guidelines start from gross income (with statutory adjustments) and account for: - Wages, salaries, commissions, bonuses, overtime - Self-employment net income - Pension, retirement, and Social Security benefits - Rental and investment income - Unemployment, workers' comp, disability - Imputed income if a parent is voluntarily unemployed/underemployed Standard deductions before the support formula runs: - Federal/state income tax - Social Security and Medicare (FICA) - Mandatory union dues - Health insurance premiums for the child - Other court-ordered support obligations ## Add-ons most states bolt onto the base number - **Health insurance** for the child (split proportionally to income) - **Childcare costs** (work-related daycare) - **Uninsured/extraordinary medical expenses** - **Educational expenses** (private school, tutoring) — case-by-case - **Visitation travel costs** — for long-distance parents in some states ## Shared parenting time can change the math Most states reduce the support payment as the non-custodial parent's overnight time goes up — but not in a smooth, linear way. Many states have "cliffs" at specific overnight thresholds (e.g., 30%, 40%, 50%) where the formula switches from a standard payment to a shared-time formula. Whether you cross a threshold by even one overnight a year can change support by hundreds of dollars per month. ## Deviation from the guidelines The number the formula produces is a **rebuttable presumption**, not a hard floor or ceiling. Either parent can ask the court to deviate up or down by showing factors like: - A child's special medical or educational needs - Extraordinary income or expenses outside the formula - A parent's significant other obligations - A parenting plan that already addresses costs differently Most judges stick close to the guideline, but meaningful deviations happen when the facts justify them. ## Modifying support later Child-support orders aren't permanent. Most states allow modification when there's a **substantial change in circumstances** — usually a change of 15%+ in either direction. Common triggers: - Job loss or significant pay cut (or significant raise) - A change in custody/parenting time - A child's emancipation - New medical needs - A parent retires ## Enforcement is aggressive Once a child support order is in place, ${s.name}'s child-support enforcement agency has powerful tools: - Income withholding directly from paychecks - Tax refund interception (federal and state) - Driver's license suspension - Professional license suspension - Passport denial - Liens on real and personal property - Contempt of court — including jail ## What you should do Run the numbers BEFORE you agree to anything. Most Illinois family-law attorneys can pull up the state's guideline calculator and produce a realistic estimate in minutes. Going in blind to a settlement conference — or worse, to court — without knowing what the formula says is a recipe for an avoidable bad outcome. --- *This guide is general information about Illinois law as of early 2026 and is not legal advice. Child-support guidelines are revised periodically and individual cases involve detail-heavy calculations. Talk to a licensed Illinois family-law attorney about your specific situation.*