RESOURCES

Illinois Child Support Calculator

An estimate of guideline child support under 750 ILCS 5/505, using the current HFS income shares schedule.

Before you rely on a number

01 — Guidelines are a starting point

Courts follow the formula in most cases, but they can deviate with written findings — for extraordinary medical costs, prior support orders, or income that the schedule doesn't capture well.

02 — 50/50 time ≠ zero support

Equal parenting time doesn't automatically mean no one pays. The schedule is only part of the calculation — income differences still drive an obligation.

03 — The law changes in 2027

Graduated shared-parenting adjustments take effect January 1, 2027. This estimator applies current law; timing can matter to your case.

How Illinois calculates child support

Illinois uses an income shares model. Rather than taking a flat percentage of one parent’s paycheck, the calculation starts from both parents’ combined net income and asks what the parents together would have spent on the children if the household had stayed intact. That amount, called the basic support obligation, comes from a schedule published by the Illinois Department of Healthcare and Family Services. The obligation is then divided between the parents in proportion to their incomes.

If one parent earns 70% of the combined net income, that parent is responsible for 70% of the basic obligation. When the child lives primarily with the other parent, the higher-earning parent pays their share as support.

What counts as income

Net income means gross income from all sources minus taxes, calculated either under a standardized formula or, when the parties agree or the court orders it, using an individualized tax calculation. Income includes wages, bonuses, commissions, self-employment income, rental income, and most other money coming in. It does not include benefits from public assistance programs.

A parent who is voluntarily unemployed or underemployed can have income imputed, meaning the court uses what the parent could be earning rather than what they report. Income disputes are the most contested part of most child support cases, and the calculator is only as accurate as the numbers you put in.

Overnights and shared parenting

The number of overnights each parent has changes the result. Under current law, when each parent has at least 146 overnights a year, the basic support obligation is multiplied by 1.5 to reflect the cost of maintaining two households, and each parent’s share is then adjusted based on the percentage of time the child spends with the other parent.

That threshold is changing. Beginning January 1, 2027, the shared parenting calculation starts at 110 overnights, with a graduated adjustment between 110 and 145 overnights and the full shared parenting formula at 146 or more. This calculator runs today’s rules. If your overnights fall between 110 and 145, the 2027 change will affect your number. Read about the 2027 child support changes.

What the basic obligation does not cover

The guideline amount is meant to cover ordinary day-to-day costs. Health insurance premiums, uninsured medical expenses, child care needed for a parent to work, and extracurricular and school expenses are handled separately. Courts typically allocate them between the parents in proportion to income, on top of the basic support figure. A support order that does not address these categories specifically is a support order that will be back in court.

When the court departs from the guideline

The guideline amount is presumed correct, but a judge can deviate when applying it would be inequitable. Common reasons include extraordinary medical needs, a child’s own income or resources, or a parent’s obligation to support other children. Any deviation has to be explained in the order.

When to talk to an attorney

The formula is public. The inputs are where cases are won and lost. If you are not sure what your co-parent actually earns, if either of you is self-employed, if your parenting time is close to one of the overnight thresholds, or if you are being asked to agree to a number that seems off, get advice before you sign anything.

LaRocque Law represents both parents seeking support and parents paying it, in Cook, DuPage, and Will Counties. Visit our child support practice page or schedule a consultation.

This calculator is an estimate for general information and is not legal advice. Using it does not create an attorney-client relationship.

Which schedule this calculator uses

The basic support obligation comes from the Illinois Schedule of Basic Obligations published by the Department of Healthcare and Family Services, and this calculator uses the 2026 schedule. HFS updates the table periodically, so an older worksheet, a printed chart, or another site’s calculator can return a different number from the same incomes. If your figure does not match one a lawyer or the court produced, the first thing to check is which year’s schedule each one used and whether net income was calculated the same way.

With round numbers: Parent A nets $6,000 a month and Parent B nets $3,000, they have one child, and the child lives mainly with Parent B. Combined net income is $9,000 and Parent A earns two-thirds of it. The 2026 schedule puts the basic support obligation for one child at that income at $1,585 a month, so Parent A’s guideline payment is two-thirds of that, about $1,057, before health insurance and other add-ons are divided. That is exactly the math this calculator runs, with your numbers.

Common mistakes that throw the number off

Entering gross pay instead of net. The schedule runs on net income, and the difference between gross and net at most Chicago incomes is several hundred dollars a month per parent, which moves the result more than any other single input.

Counting overnights by a typical week instead of the whole year. The statute counts nights the child sleeps at each home over a full year, including holidays, school breaks and summer. A schedule that looks like 40 percent on paper often lands at 130 to 140 overnights once the calendar is counted, and that is on the wrong side of the 146 line under current law.

Treating equal time as no support. Under Illinois’s shared-parenting formula, 50/50 time with unequal incomes still produces a payment from the higher earner.

Leaving out the add-ons. The guideline figure does not include the child’s health insurance premium, uninsured medical costs, work-related child care, or school and activity expenses, all of which are typically divided in proportion to income on top of it.

Forgetting a prior support order. Child support or maintenance a parent already pays under another order is deducted before the schedule is applied.

Comparing numbers from different years. See the schedule note above.

Questions about this calculator

Is this the official Illinois child support calculator? No. HFS publishes its own estimator. This one uses the same statute and the same schedule, shows the steps, and lets you test how overnights and income changes move the result. Only a judge decides what a support order says.

Does it include the January 2027 changes? Not yet. It runs the law in effect today. If your parenting time falls between 110 and 145 overnights a year, the 2027 graduated adjustment will change the calculation, and we explain how in the post linked above.

Why is my number different from the one my co-parent got? Almost always the inputs: one of you used gross income, counted overnights differently, or handled a prior support order or the insurance premium differently. Run it again with the same assumptions and the results will match.

A shared-parenting example

Take the same parents from the example above: Parent A nets $6,000 a month, Parent B nets $3,000, one child, and the 2026 schedule puts the basic support obligation at $1,585. Now give Parent A 146 overnights a year, exactly 40 percent, and Parent B the other 219.

Because each parent has at least 146 overnights, the shared physical care formula applies. First, the basic obligation is multiplied by 1.5 to reflect the cost of two households: $1,585 becomes $2,377.50. Second, that figure is split by income: Parent A’s share is two-thirds, $1,585, and Parent B’s is one-third, $792.50. Third, each parent’s share is multiplied by the percentage of time the child spends with the other parent. Parent A owes 60 percent of $1,585, which is $951. Parent B owes 40 percent of $792.50, which is $317. The two obligations are netted, and Parent A pays Parent B the difference: $634 a month.

Compare that to $1,057 with the child living mainly with Parent B. The move from 145 overnights to 146 cuts the payment by about 40 percent under today’s law, which is why overnights get counted so carefully and why the January 2027 change matters: from 2027 the adjustment phases in between 110 and 145 overnights instead of switching on all at once at 146.

How net income is calculated

Net income under the statute is not take-home pay. It is gross income from every source minus taxes, and the taxes are calculated one of two ways. The standardized tax amount treats each parent as a single filer taking the standard deduction and applies the federal and state income tax and FICA that go with it; it is the default and it is what this calculator approximates when you enter gross income. The individualized tax amount uses the parent’s actual filing status, deductions, and credits, and applies when the parents agree to it or the court orders it. The two methods can produce different net figures for the same paycheck, and the difference is a common argument in support cases.

Two adjustments come after tax. Maintenance paid to the other parent is subtracted from the payor’s net income and added to the recipient’s before the schedule is applied, which is why maintenance is calculated first when both are at issue; the Illinois spousal maintenance calculator covers that step. Child support or maintenance a parent actually pays under an order for another family is also deducted, and a parent supporting other children in their own household may receive a multi-family adjustment.

Things that do not reduce net income for this purpose: 401(k) contributions, health insurance premiums (those are handled as an add-on, not an income deduction), union dues, and voluntary payroll deductions. Gross income is also wider than a salary. Bonuses, overtime, commissions, self-employment income after legitimate business expenses, rental income, and investment income count, and a parent who is voluntarily unemployed or underemployed can have income imputed based on work history, qualifications, and the local job market. For a self-employed parent, the court looks at the business’s actual earnings, not the draw the owner chose to take.

When child support changes or ends

Child support does not stay fixed for the life of the order. Either parent can ask the court to modify it on a substantial change in circumstances or where a change is in the best interest of the child: a real, involuntary change in either parent’s income, a change in the parenting schedule that crosses an overnight threshold, a child’s changed needs, or the emancipation of an older child when the order covers more than one. A modification runs only from the date the other parent is served with notice of the petition, not from the date the circumstances changed, so waiting to file costs money in both directions. Our post-decree modification page covers how the process works.

Support for a child ends when the child turns 18, or, if the child is still in high school at 18, when the child graduates or turns 19, whichever comes first. It does not end automatically when the payor retires, remarries, or has another child, and it does not end for the older child in a multi-child order until the order is modified. Past-due support does not go away: it accrues interest, it cannot be discharged in bankruptcy, and it is collected through income withholding and the State Disbursement Unit.

Two obligations can continue past 18. A court can order either or both parents to contribute to a child’s college or trade school expenses under Section 513, based on the parents’ and the child’s resources, and can order support for an adult child with a disability under Section 513.5. Neither is automatic; each has to be requested, and the college contribution has its own limits, including a cap tied to the cost of the University of Illinois at Urbana-Champaign.