Illinois Child Support Calculator

How Illinois calculates child support

Illinois sets child support with the Income Shares Model, and we have read the guideline that says so, which means both parents' incomes are combined, and each parent covers the share of the total obligation that matches their share of that combined income. Here is what that looks like in practice.

The Income Shares Model starts from an estimate of what the children would have received had the household stayed intact, then splits that figure between the parents. The calculation runs in three steps. Both parents' monthly incomes are added together. A basic support obligation for that combined figure and that number of children is set by the state's own guideline. Each parent is then responsible for the percentage of the obligation that matches their percentage of the combined income.

Because the obligation is divided by income share rather than assigned to one side, the receiving parent's earnings matter as much as the paying parent's. A parent bringing in 70 percent of the combined income carries roughly 70 percent of the total obligation. The parent the children live with most is treated as already spending their share through daily care, so only the other parent's share is ordered as a payment. That is why closing the income gap between two parents lowers the payment even when neither parent's own income falls.

Four things are then layered on top of the base figure: health insurance premiums covering the children, work-related childcare, support already being paid under an earlier order for other children, and, in most states, the number of overnights each parent has.

The figure Illinois's own guideline works from is combined net income, under 750 ILCS 5/505(a)(1.5), applied to the Income Shares Schedule Based on Net Income.

What moves the number in Illinois

• Both parents' monthly incomes, and the gap between them
• Number of children covered by the order
• The paying parent's share of overnights
• Health insurance premiums covering the children
• Work-related childcare for the children, under a rule this estimate does not apply
• Support already ordered for children from another relationship

Income limits and judicial discretion

Illinois does put a figure at the top and it is not a cap. The Income Shares Schedule stops at $27,374.99 of combined monthly income, and 750 ILCS 5/505(a)(3.5) gives the court discretion above it "except that the basic child support obligation shall not be less than the highest level of combined net income set forth in the schedule". That exception is what turns the top band into a statutory minimum, so the discretion runs upward from it and not down. Check the unit before comparing it with another state, because Illinois states this one at combined NET income rather than gross, which is the same basis its whole schedule is read at and a lower number than the gross equivalent. Illinois gives judges a moderate amount of room on custody and parenting time, so expect the order to start from the guideline figure and move with the facts of the case.

Illinois child support examples

These three examples run through the same Illinois calculator on this page, so the figures match what the tool returns for the same entries. Each example changes one thing against the one before it, so you can see which lever moved the result. All three assume a standard schedule of 80 overnights a year with the paying parent, and Illinois's own parenting-time rule is applied to every figure below rather than left off it. At this count the rule does not reach, so these are complete guideline amounts rather than amounts waiting for an adjustment. The table further down the page is where the count starts to move the number, and it shows where.

Comparing the first two examples shows what a second child is worth in Illinois: the order moves from $773 to $1,158a month on identical incomes. The third example raises the paying parent's earnings and adds health insurance and childcare, which are credited back against the obligation rather than added on top of it.

How parenting time changes support in Illinois

Illinois adjusts support for parenting time, and we compute the adjustment, because we have read the rule out of the state's own published guidelines rather than inferring it. The mechanism is a cliff. Below 146 overnights the calculation runs on the standard income shares calculation and parenting time does not enter it at all. At 146 overnights it switches to the shared physical care calculation, which multiplies the basic obligation by 1.5, divides it between the parents in proportion to their net incomes, and then multiplies each parent's share by the percentage of time the child spends with the other parent. The two figures are offset and the parent with the higher one pays the difference. The figure steps at that boundary rather than sliding toward it, so a single night can be worth several hundred dollars a month.

The part that catches parents out is that BOTH parents have to clear 146 overnights, not just the one asking for the adjustment. Under 750 ILCS 5/505(a)(3.8) the shared route turns on each parent exercising 146 or more overnights per year with the child. Work that through and the result is genuinely counter-intuitive, and you can see it in the last row of the table above. A parent with 250 overnights leaves the other parent 115, 32 percent of the year, which is below the bar, so the shared route never comes out and the figure goes back up to about where it was at 52 overnights. Getting well past an even split can cost you the adjustment an even split would have given you. If you are negotiating toward a particular number of overnights, check what the schedule leaves the other parent, not only what it gives you.

Note the wording of the boundary, because it is not the same in every cliff state and it decides cases that sit on it. Illinois's rule is each parent exercising 146 or more overnights per year with the child, so a parent at exactly 146 qualifies. Other states word the same kind of rule as "more than", which excludes a parent sitting exactly on the number: West Virginia's threshold is 127 days and a parent with exactly 127 does not clear it. One night either side of a threshold is where contested schedules tend to end up, so it is worth reading your own state's phrasing rather than a summary of it.

Two further Illinois rules are worth knowing before you read the number above. The schedule is read from combined NET income rather than gross, and the figure comes from a $50-wide band rather than being interpolated, so two families $49 apart in net income get the same obligation and two families $1 apart across a band edge do not. Health insurance for the children counts as reasonable in cost only up to 5 percent of the providing parent's gross income under 750 ILCS 5/505(a)(4)(G), and a parent whose net income is below 133 percent of the federal poverty guideline, or whose child is on Medicaid, is not ordered to contribute to private coverage at all.

Overnights are the second biggest lever after income, and they are the one parents most often underestimate. The reasoning is straightforward: a parent who has the children a third of the year is already paying for food, utilities, and a bedroom during that time, so the transfer payment to the other household falls to avoid charging twice for the same costs.

The table below runs one family through the Illinois guideline at 6 parenting-time levels. Income is held at $5,000 and $3,000 a month with two children, so the only thing changing between rows is the number of overnights. It follows Illinois's own published rule, and the state's worksheet linked below is still the document a court works from.

The size and the shape of that movement are what parenting-time disputes and support disputes are usually arguing about at the same time, in different clothing.

Where Illinois starts on parenting time

Illinois does not presume equal parenting time. That is our own record rather than Illinois's own custody law. Courts decide the schedule on the best interests of the children, so the overnight count is established case by case rather than assumed. Parents who expect substantial time should treat it as something to be negotiated deliberately, and the section above is what Illinois's own guidelines do with the count you end up with, which is worth reading before you agree to one.

Getting a child support order in Illinois

The guideline figure is only half the picture. When the order actually arrives, and what it costs to argue about it, vary quite a bit from state to state, and both shape what a family lives on in the meantime.

Residency required

3 months

Waiting period

None

Typical uncontested

4 months

Typical contested

about 1.2 years

Support before the case is finished

You need 3 months of residency in Illinois before you can file, and no statutory waiting period applies before a judge can finalize the divorce. A contested case in Illinois runs about 1.2 years on average, against 4 months when the parents agree. That gap is why temporary support matters. A judge can enter a temporary order early in the case, calculated on the same guideline, so the children are covered while the rest of the case is worked out. If money is tight now, a temporary order is usually the fastest relief available, and waiting for the final judgment can mean months without support.

What it costs to contest the number

Family law attorneys in Illinois typically run $250 to $500 an hour, and mediation costs roughly $275a session. Worth doing the arithmetic before digging in: a handful of billable hours on each side can cost more than a full year of the amount being argued over. Where the disagreement is genuinely large, or where one parent's income is hard to pin down, representation earns its keep. Where the gap between the two positions is a few dozen dollars a month, mediation or a negotiated agreement almost always leaves both households better off. Our record carries collaborative divorce as available in all fifty states, so it says nothing specific about Illinois; whether trained collaborative attorneys practise near you is a local question. Where it is on offer, both parents commit in writing to settle without litigation and use shared financial experts rather than competing ones.

Changing or enforcing an Illinois order

Modifying an existing order

A child support order is not permanent, but it also does not adjust on its own. Either parent can ask the court to recalculate, and the general standard across states is a substantial and continuing change in circumstances since the last order. Job loss, a significant raise, a change in the parenting schedule, a new child support obligation for another child, and a change in the children's medical or childcare costs are the changes that most often qualify.

Two points catch parents out. The first is that a modification usually takes effect from the date the request is filed, not the date the circumstances changed, so waiting to file means absorbing the gap. The second is that the obligation continues in full until a judge signs a new order. An informal agreement between parents to pay less does not bind the court, and arrears can still accrue against the paying parent for the difference.

Enforcement

Enforcement runs through Illinois's child support agency as well as the courts. Federal law requires every state to run a child support enforcement program with a common set of tools, which is why the remedies look broadly similar from state to state: income withholding straight from wages, interception of federal and state tax refunds, reporting to credit bureaus, suspension of driver's and professional licenses, liens against property, and contempt proceedings for willful non-payment. Income withholding is the default for new orders in most cases rather than a penalty applied after a missed payment.

Recent Illinois guideline changes

Illinois guideline authority and official worksheet

The Illinois child support guideline in our data is:

• 750 ILCS 5/505

That authority controls, and the worksheet published under it is the document a court works from. The estimate on this page models the guideline, it does not replace the worksheet.

Where to get the official worksheet

Every state publishes a child support worksheet or an official calculator, and that document is what a judge or the state agency works from. Illinois publishes the form below, and it is the one to fill in once your figures are settled. The estimate on this page models the same guideline so you can plan around it first.

• Illinois Department of Healthcare and Family Services Child Support Estimator, which publishes a guided version for parents and a direct-entry version for attorneys
• Illinois courts , the state judiciary site from our Illinois source record.
• Office of Child Support Services, U.S. Administration for Children and Families, which maintains the directory of state child support agencies.
• National Conference of State Legislatures, child support guideline models by state, which publishes its own comparison of the guideline model each state uses, so you can check ours against it.

How we calculate this estimate

We apply the guideline model your state actually uses, and the models differ more than most summaries suggest. Most states follow the Income Shares Model: both parents' monthly incomes are combined, a basic support obligation is drawn from that combined figure and the number of children, and each parent covers the share that matches their portion of the combined income. Which income figure gets combined is the state's own to define and it is not the same one everywhere, so this page names it for your state where the guideline has been read and does not guess at it where it has not. Percentage of Income states apply a set rate to the paying parent's income alone, and Nevada's tiered version steps that rate down across income brackets. The Melson Formula reserves a self-support amount for each parent before dividing what is left. Some states do neither: North Dakota reads a dollar figure off a table keyed to one parent's net income, and California publishes a single algebraic formula with no schedule behind it. Which one your state is on is named on its own page rather than inferred from a list here. Credits for health insurance and childcare are applied where the state's own guideline builds them into the order, along with any income cap the state sets, and the list of what moves the number on each state's page names the levers that actually move that state's figure. Parenting time is computed in the states whose own guideline we have read and implemented, and in no others.

What the estimate assumes for Illinois

• Income figures are gross monthly, before taxes, counting the sources your state includes.
• Parenting time moves the figure only where we have read and implemented the state's own rule. The parenting-time section further down this page says which case this state is in, and where no adjustment applies the estimate is the amount before one. We previously reduced support past 146 overnights on a coefficient of our own. 146 turned out to be a single state's statutory threshold applied to all fifty, the size of the reduction had no legal source anywhere, and the mechanisms states actually use are not variations on one rule. Among the ones we have now read: a worksheet that switches at a threshold both parents must clear, an offset applied continuously with no trigger, a threshold that does nothing below it and slides above it, a term written into the guideline formula itself so there is no unadjusted amount at all, no parenting-time term anywhere, and a formula prescribed by statute whose text we do not have. That list is what we have read rather than what exists, and it has grown with every state checked. We removed ours rather than defaulting it, and we publish each state's adjustment as that state's own rule is verified.
• North Carolina is one of the verified threshold cases, at 123 overnights under the guidelines adopted pursuant to N.C. Gen. Stat. 50-13.4(c1). The threshold has to be cleared by both parents, which is why a parent well past an even split can fall outside shared care entirely.
• Texas has no parenting-time adjustment at all, because its guideline has none. Tex. Fam. Code 154.125 runs on the obligor's net resources and the number of children, and the state's own calculator has no field for overnights. Possession time enters only as a discretionary deviation factor, Tex. Fam. Code 154.123(b)(4).
• Georgia has a mandatory parenting-time adjustment whose formula we do not have. O.C.G.A. 19-6-15(g), effective January 1 2026, requires the court to adjust the noncustodial parent's basic obligation wherever there is a court-ordered parenting time schedule, with the result entered on Child Support Schedule C. Applying arithmetic of our own in place of a prescribed formula would be worse than applying none, so the Georgia estimate is the presumptive amount before that adjustment.
• Where a state's own schedule has been transcribed, the basic obligation is read straight off it. Where it has not, the figure comes from a national approximation of the tables courts read from, and the source panel on that state's page says which of the two you are looking at. That approximation has been measured against the seven transcribed schedules keyed to the same thing it is, at 546 income and family-size combinations. It missed them by 32 to 86 percent on average, and it missed them in both directions at once: at every income from $1,500 to $6,000 of combined monthly income it came in under at least one of those schedules and over another, then above all seven from $8,000 up, reaching 69 to 240 percent above those states' own tables at $30,000. So a modeled figure at a high combined income is the least reliable number this calculator returns, and near $6,000 is where the approximation lands closest.
• Where a state sets an income ceiling, we clamp income at it. That is a fair model of a real cap and a poor one of everything else, so two states are handled differently. New York's $193,000 of combined parental income is the point above which a court may consider the additional income, not a limit on what it can order, and our figure there is the amount the guideline produces at the threshold. New Jersey's Appendix IX-F schedule ends at $3,600 of combined weekly net income, and courts are instructed in capital letters not to extrapolate past it, so we read the obligation at the schedule's last row and treat the result as the minimum basic support award rather than as a guideline amount. Appendix IX-A requires a New Jersey court to add to that minimum from the income above the ceiling. Modeling what a court adds is not something we can do honestly, because it turns on statutory factors rather than on arithmetic. Above the New Jersey line our figure is therefore a floor, and above the New York line it is not one: the addition New Jersey requires is what makes its schedule figure a minimum, and no New York instrument says an award may not come in below the amount at the threshold. Both figures read as the low end of a realistic range and only one of them is a floor a reader can count on.
• The same schedule can also stop short at the bottom. New Jersey publishes no award figure below $180 of combined weekly net income, where the court sets the amount from the paying parent's income and living expenses within a published range. Our estimate at that income is a modeled figure with nothing from the state to check it against, and it says so.
• The result is a guideline number. Judges can deviate from it when the facts justify a different amount.

Where the estimate stops

Your state's official worksheet is the controlling document, and a court order can land somewhere other than any guideline estimate. Use this to prepare, then confirm the figure with a licensed family law attorney or your state's child support agency.

Read the full methodology for how every calculator on the site is built.

Sources

Illinois courts and statutes

• illinoiscourts.gov
• 750 ILCS 5/504 maintenance formula
• 750 ILCS 5/505
• 750 ILCS 5/505(a)(3.8)
• hfs.illinois.gov
• hfs.illinois.gov
• hfs.illinois.gov

Where to read more

Background reading, not where the figures above came from. No number on this page is taken from any of these.

• National Conference of State Legislatures, child support guideline models by state
• Office of Child Support Services, U.S. Administration for Children and Families
• American Bar Association, Section of Family Law

About this page

Written by Barron Hansen

I am an app developer who is dedicated to building the highest-value, most accurate web apps possible, that people want to use every day.