Illinois Child Support Guide — Income Shares

By Bilal Butt, founder. Last verified: October 2026.

Illinois uses an income-shares model (750 ILCS 5/505, since 1 July 2017). There is no percentage formula: the basic obligation comes from the Illinois Department of Healthcare and Family Services (HFS) Schedule of Basic Child Support Obligations, a dollar table in $50 combined-income bands. That is why this page is a guide with checked examples, not a calculator — a calculator that guessed a percentage would be inventing the schedule.

Steps

1. Each parent's monthly net income (HFS gross-to-net conversion table using standardised tax amounts, or an individualised calculation where appropriate).
2. Combined monthly net income.
3. Look up the basic obligation in the HFS schedule for that combined income and number of children.
4. Each parent's share = their share of combined net income × basic obligation. The noncustodial parent's share is generally paid; the custodial parent's share is presumed spent directly.
5. Add-ons are added and divided by the same income shares.

Schedule year matters: all schedule figures on this page are 2025 HFS schedule values, labelled as such. A claimed 2026 schedule figure from a single secondary source is not used here because no official HFS 2026 schedule PDF was located. The 2025 schedule's final row is $26,675.00–$26,724.99/month combined net income; above that, the court has discretion and the basic obligation is not less than the highest schedule level — do not extrapolate a percentage.

Worked example — standard case (2025 schedule)

Parent A net $5,000/month, Parent B net $3,000/month, 2 children, A has 90 overnights and B has 275 (shared-care threshold not met). Combined net $8,000/month. Schedule basic obligation for 2 children at $8,000 (2025 row $7,975.00–$8,024.99) = $2,130/month. A's share 62.5%, B's 37.5%. A (noncustodial) pays 62.5% × $2,130 = $1,331/month basic support, before add-ons.

Shared care — 146 nights now, 110 nights from 1 January 2027

Shared physical care applies when each parent exercises 146 or more overnights per year (about 40% of time). Formula: (1) basic obligation × 1.5; (2) apportion by each parent's income share; (3) multiply each parent's share by the other parent's share of parenting time; (4) offset — the parent owing more pays the difference. Below 146 overnights each, the standard calculation applies with no timeshare credit. Courts look at actual parenting time, not just the written plan.

Upcoming change (not current law): Public Act 104-0733 lowers the threshold to 110 overnights (or overnight equivalents) from 1 January 2027, with the 1.5 multiplier unchanged and a sliding uplift (10% at 110–114 overnights down to 2% at 140–145) for parents under 146 overnights, capped at the basic-guideline amount. Do not apply the 110-night rule to cases decided before that date.

Worked example — shared care (2025 schedule)

Combined net $10,000 → basic $2,477; × 1.5 = $3,715.50 shared-care obligation. A (60% income, 182 nights) share $2,229.30 × B's time (183/365 = 50.14%) = $1,117.70; B (40% income, 183 nights) share $1,486.20 × A's time (182/365 = 49.86%) = $741.06. Offset: A pays $1,117.70 − $741.06 = $377/month. Near-equal time does not mean $0 — the income gap still produces a payment.

Low-income floor, other children, add-ons, end of support

Low-income floor (current law): where an obligor's actual or imputed gross income is at or below 75% of the federal poverty guideline for one person, the rebuttable presumption is a minimum of $40/month per child, capped at $120/month total divided equally among the obligor's children. There is a $0-order presumption where the parent has no gross income, receives only means-tested assistance, or cannot work due to medically proven disability, incarceration or institutionalisation. From 1 January 2027 the same Act raises the floor threshold from 75% to 100% of the poverty guideline. Other children: the multifamily adjustment is made to the parent's net income (support actually paid under an order, or the lesser of support actually paid or 75% of the guideline amount on that parent's income alone, without an order) — not a Texas-style percentage table. Add-ons (health-insurance premiums, work/education-related childcare, extraordinary expenses) are added to the basic obligation and divided by income shares; every order must include a health-insurance provision. College expenses are separate under §513 (petition-based, factor-driven). End: the order must state a termination date no earlier than the child's 18th birthday; if the child will not graduate high school until after 18, no earlier than the earlier of graduation or age 19.

Sources: 750 ILCS 5/505; Illinois HFS 2025 Schedule of Basic Obligations and 2025 Gross-to-Net Conversion Table; Public Act 104-0733 (110 nights from 1 Jan 2027). HFS 2025 schedule · §505 text

How to use this guide

Work in four steps. First, convert each parent's gross income to net income using the HFS gross-to-net conversion table (standardised tax amounts) or an individualised calculation where appropriate. Second, add the two net incomes to get combined monthly net income. Third, look up the basic obligation in the HFS Schedule for that combined income and number of children — the schedule is in $50 combined-income bands, so find the band your combined income falls in, not the nearest round number. Fourth, split the basic obligation by income shares and add add-ons divided the same way. The noncustodial parent's share is generally paid; the custodial parent's share is presumed spent directly on the child.

Worked examples in a table

Shared-care illustration from the research file: where both parents have 146 or more overnights, the basic obligation is multiplied by 1.5 and then offset between the parents, giving about $377/month in the checked example (not $380). The exact offset depends on each parent's income share and the 1.5× basic figure, so the $377 figure is an example, not a rate to apply blindly.

Common mistakes

• Using a percentage. Illinois has used income shares since 1 July 2017. Any pre-2017 percentage table is obsolete and must not be used.
• Using the 110-night rule now. Shared care is 146 or more overnights under current law. The 110-night rule in Public Act 104-0733 takes effect only on 1 January 2027, with a sliding uplift and a cap at the basic-guideline amount.
• Using an unlabelled schedule year. Schedule values change. Every schedule figure on this page is a 2025 HFS value and is labelled as such.
• Forgetting the low-income floor. The statutory floor is $40/month per child, capped at $120/month total, where the obligor's gross income is at or below 75% of the federal poverty guideline for one person (750 ILCS 5/505(3.3a)). From 1 January 2027 that threshold rises to 100% — current pages must still use 75%.
• Applying the schedule above its ceiling as if it continued. The 2025 schedule's final band ends at $26,724.99 of combined income. Above that, the court has discretion; there is no published schedule row to extrapolate.

How courts deviate

Illinois courts may deviate from the schedule for the child's best interests, considering factors including the child's needs, the parents' resources and earning capacity, the standard of living, and special expenses. For maintenance, a court that deviates from the guideline must state the guideline amount and duration and its reasons — the same discipline of showing the starting point applies here: this guide shows the schedule figure first, then the factors that can move it.

When to hire a lawyer

Talk to an Illinois-licensed attorney before relying on a schedule figure if income must be imputed, if either parent is self-employed or has variable income, if shared care is near the 146-night threshold, if add-ons are large, or if the case involves the January 2027 rule change. This site cannot recommend a specific lawyer and does not take referral fees.

Frequently asked questions

These questions are shown on the page in full. They are not marked up as FAQ structured data.

Why is there no Illinois child support calculator?

Because Illinois law is a dollar schedule table, not a percentage. A calculator would have to guess the schedule. This guide shows the method and checked 2025 schedule examples instead.

Is 110 nights the shared-care threshold?

Not yet. It is 146 nights under current law; 110 nights applies only from 1 January 2027 under Public Act 104-0733.

What schedule year are the figures?

2025 HFS schedule values, labelled as such throughout. A single secondary source's claimed 2026 figure is not used.

Change log

Related

Other pages for the same jurisdiction or the same topic:

• Illinois Maintenance Calculator