Child Support — Lake County, IL
By Deanna Bowen · Updated August 2026 · 20+ years in Lake County family law
How child support is calculated in Illinois: 750 ILCS 5/505(a)(1.5) directs the court to find each parent’s monthly net income, add them together, read the basic obligation off the state’s schedule for that combined income and number of children, and prorate it between the parents. If each parent has 146 or more overnights, a different formula applies. Lake County attorney Deanna Bowen walks the math.
Almost everything frustrating about Illinois child support comes from one fact: the number is not a percentage of the paying parent’s paycheck. It has not been since July 1, 2017, when Public Act 99-764 replaced the old obligor-percentage model with income shares. Yet the old figures — 20% of net income for one child, 28% for two, 32% for three — are still repeated constantly, including by people who ought to know better.
If someone has quoted you a figure built on one of those percentages, the method behind it is not the law any more — and a number produced the wrong way is not something to plan around, however close it might land by chance.
The fast version:
- Support is built from both parents’ incomes, not just the payer’s.
- The steps are set by statute: net income → combine → look up the schedule → prorate.
- 146 overnights each flips you into an entirely different formula, with a 1.5 multiplier.
- 50/50 parenting time does not mean nobody pays.
- The dollar tables are administrative and change — the ones in force now took effect March 20, 2026.
The Income-Shares Model: Three Steps From Paychecks to a Support Number
Section 505(a)(1.5) of the Illinois Marriage and Dissolution of Marriage Act spells the sequence out. The court computes the basic child support obligation “by taking the following steps”:
“(A) determine each parent’s monthly net income; (B) add the parents’ monthly net incomes together to determine the combined monthly net income of the parents; (C) select the corresponding appropriate amount from the schedule of basic child support obligations based on the parties’ combined monthly net income and number of children of the parties; and (D) calculate each parent’s percentage share of the basic child support obligation.”
Then comes the sentence that explains why only one parent writes a check:
“Although a monetary obligation is computed for each parent as child support, the receiving parent’s share is not payable to the other parent and is presumed to be spent directly on the child.”
Both parents are assigned a share. The receiving parent’s share is presumed to be spent already — on feeding, housing, and clothing the child day to day — so only the other parent’s share moves as a payment. In most cases the receiving parent is the one with the majority of parenting time, though the statute frames the rule around the receiving parent rather than the parenting-time count.
Step 1 — net income, and which method gets used
Gross income under § 505(a)(3) is income from all sources. Getting from gross to net happens one of two ways, and they are not interchangeable.
The standardized method is the default: the court takes the parent’s gross income to the Illinois Department of Healthcare and Family Services Gross to Net Income Conversion Table, which applies assumed federal and state taxes, Social Security, and Medicare. It applies the tax assumptions the statute prescribes rather than your actual return. It is fast and consistent — but it is not the last word on your statutory net income, because maintenance and support obligations for children of another relationship can adjust the figure the guidelines are ultimately run on.
The individualized method uses a parent’s actual tax picture instead. Section 505(a)(3)(E) permits it, but not on request alone — the statute allows an individualized determination where the parties agree (“if they jointly stipulate for the record their concurrence on a computation method”) or where the court determines it after hearing. If it is used, all relevant tax attributes — filing status, dependency exemptions, standard versus itemized deductions — “shall be as the parties agree or as the court determines.”
If a parent is voluntarily unemployed or underemployed, the court can impute income rather than accept the depressed figure. That is not automatic either; imputation requires written findings identifying the basis for the figure.
Step 2 — combine, and look up the schedule
The two net incomes are added into a combined monthly net income. That figure and the number of children point to one row of the HFS Income Shares Schedule of Basic Child Support Obligations, a grid that cross-references bands of combined net income against the number of children to produce the basic obligation.
⚠️ Use the current table, and use the real one. The schedule and the conversion table are administrative instruments that HFS revises; the versions in force as of August 2026 took effect March 20, 2026 and are published on the HFS income shares page. Third-party calculators may be running on an older revision — check the effective date on whatever tool you use against the current HFS schedule and conversion table, because an outdated table makes every number downstream wrong.
If the parents’ combined adjusted net income runs past the top of the schedule, § 505(a)(3.5) lets the court use its discretion — with a floor: “the basic child support obligation shall not be less than the highest level of combined net income set forth in the schedule.”
At the other end, § 505(a)(3.3a) creates a rebuttable presumption of a minimum monthly obligation per child, subject to a maximum total for that obligor divided among the children, where the obligor’s actual or imputed gross income falls at or below a percentage of the federal poverty guidelines. Because those amounts are set by statute and can be amended, check the current text of § 505(a)(3.3a) rather than a figure quoted in an article.
Section 505(a)(3.3b) goes further in defined circumstances. It describes parents with no gross income, parents who receive only means-tested assistance, and parents who cannot work due to a medically proven disability, incarceration, or institutionalization — and provides a rebuttable presumption that the minimum order is inapplicable and that a zero dollar order is entered instead. Like the minimum-order presumption it can be rebutted, and which of those descriptions actually fits a given parent is exactly the sort of question worth advice on rather than assumption.
Step 3 — prorate
Each parent’s share is their net income divided by the combined net income. That percentage, applied to the basic obligation, is that parent’s dollar share.
Worked Examples: The Standard and Shared-Physical-Care Calculations, Step by Step
Here is the same family run through both formulas, so you can see what the parenting schedule actually does to the money.
The facts, held constant: one child. Parent A’s monthly net income is $6,000; Parent B’s is $4,000. Combined monthly net income is $10,000. Parent A’s share is 60%, Parent B’s is 40%.
How to read these examples. The one number I am deliberately not printing is the basic obligation itself, because HFS revises the schedule and any figure quoted in an article goes stale. So the examples below call it S — the schedule amount for your combined net income and number of children, which you look up on the current HFS schedule (effective March 20, 2026). Everything else is the real statutory arithmetic. What this shows you is the shape of the calculation and how much the parenting schedule moves it — not a finished order. A real order also runs through income adjustments, add-ons, maintenance, obligations for other children, low-income provisions, and any deviation the court makes.
Example 1 — the standard calculation (Parent B has 100 overnights)
Parent B is under the 146-overnight threshold, so the standard § 505(a)(1.5) calculation applies. (Parent B still has substantial parenting time — “standard” here just means the shared-care formula has not been triggered.)
| Step | Result |
|---|---|
| Combined monthly net income | $10,000 |
| Basic child support obligation | S (from the schedule) |
| Parent A’s share (60%) | 0.60 × S — presumed spent directly on the child |
| Parent B’s share (40%) | 0.40 × S |
| Net payment | Parent B pays Parent A 0.40 × S per month |
Example 2 — shared physical care (Parent A has 183 overnights, Parent B has 182)
Both parents clear 146, so § 505(a)(3.8) takes over. The statute says exactly what happens:
“If each parent exercises 146 or more overnights per year with the child, the basic child support obligation is multiplied by 1.5 to calculate the shared care child support obligation. The court shall determine each parent’s share of the shared care child support obligation based on the parent’s percentage share of combined net income. The child support obligation is then computed for each parent by multiplying that parent’s portion of the shared care support obligation by the percentage of time the child spends with the other parent. The respective child support obligations are then offset, with the parent owing more child support paying the difference between the child support amounts.”
Run it:
| Step | Result |
|---|---|
| Basic obligation | S |
| × 1.5 → shared care obligation | 1.50 × S |
| Parent A’s portion (60% of that) | 0.90 × S |
| Parent B’s portion (40% of that) | 0.60 × S |
| Parent A × time with the other parent (182 ÷ 365 = 49.86%) | 0.449 × S |
| Parent B × time with the other parent (183 ÷ 365 = 50.14%) | 0.301 × S |
| Offset — the larger pays the difference | Parent A pays Parent B about 0.148 × S per month |
That offset — the larger obligation minus the smaller — is what § 505(a)(3.8) directs, and it is why the threshold matters so much.
Read that last line again. Parent A has more overnights than Parent B — 183 to 182 — and Parent A is the one paying. That is not a mistake in the arithmetic; it is the formula working as designed. Income share drives the obligation, and the 1.5 multiplier plus the cross-credit is how Illinois accounts for a child being genuinely maintained in two homes.
It is also why “we’re doing 50/50, so nobody pays support” is one of the most expensive misconceptions in Illinois family law.
A different formula again if the children are split. Where there is more than one child and each parent has physical care of at least one but not all of them, § 505(a)(3.9) applies “split physical care”: the court runs two separate support worksheets, one in each direction, then subtracts the lesser obligation from the greater — and the parent owing the greater amount pays the difference to the other.
These outputs illustrate how the formula operates. They are not a prediction of any court’s order.
The 146-overnight cliff, in one overnight
Now test the threshold itself. Keep everything the same and compare Parent B at 145 overnights against Parent B at 146 — a difference of one night.
At 145 overnights, Parent B is below the threshold, § 505(a)(3.8) never engages, and we are back to Example 1: Parent B pays Parent A 0.40 × S.
At 146 overnights (so Parent A has 219), both parents clear the threshold and the shared-care formula applies:
| Step | Result |
|---|---|
| Shared care obligation (S × 1.5) | 1.50 × S |
| Parent A’s portion (60%) | 0.90 × S |
| Parent B’s portion (40%) | 0.60 × S |
| Parent A × Parent B’s share of time (146 ÷ 365 = 40%) | 0.36 × S |
| Parent B × Parent A’s share of time (219 ÷ 365 = 60%) | 0.36 × S |
| Offset | zero — the obligations cancel exactly |
| Parent B’s overnights | Who pays | Amount |
|---|---|---|
| 145 | Parent B → Parent A | 0.40 × S |
| 146 | neither | nothing |
One overnight moves Parent B from paying 40% of the schedule amount every month to paying nothing. On these facts, that single night is worth 40% of S — every month, for years. (Change the incomes and the proportions change with them; that is the point of running your own numbers rather than trusting a rule of thumb.) The two cross-credited figures land on exactly 0.36 × S because the income split (60/40) and the time split (60/40) mirror each other, so the offset cancels to zero. Push the schedule further — to the 183/182 split in Example 2 — and the payment reverses direction entirely.
That is why the overnight count in a parenting plan gets negotiated as hard as the money, and why nobody should sign a schedule without running the support arithmetic on it first.
What Counts as Net Income — and the Add-Ons
The schedule figure is meant to cover the ordinary costs of raising a child: food, housing, clothing, everyday transportation. Several real expenses sit outside it.
On the income side. Gross income is income from all sources — wages, salary, bonuses, overtime, commissions, self-employment. For a business owner it is gross receipts less the ordinary and necessary expenses of producing that income, and the statute bars accelerated depreciation from being used to shrink it. Means-tested public assistance is excluded. So is child support or a survivor benefit received for a different child.
Maintenance changes the inputs. Where maintenance is ordered, it is added to the receiving parent’s gross income and deducted from the paying parent’s before child support is calculated. Support and maintenance cannot be run independently of each other. (Our walkthrough of the maintenance formula is here: divorce in Lake County.)
Children from another relationship. A parent supporting a child of another relationship gets an adjustment under § 505(a)(3)(F), and it works in two different ways. Where there is a court order for that other child, the deduction is the support actually paid under it. Where there is no order but the parent is in fact supporting a child they are legally responsible for, the deduction is the lesser of the support actually being paid or 75% of what the guidelines would produce for that child using that parent’s income alone. Assuming only the first branch applies is a common way to get a net-income figure wrong.
The add-ons. These are handled in addition to the basic obligation — but they do not all carry the same weight, and the difference matters when you are negotiating.
- Health care is not optional. Under § 505(a)(4)(A), the court “in addition to the basic child support obligation, shall also provide for the child’s current and future medical needs” — by ordering either or both parents to initiate coverage under an existing policy, purchase health, dental, or vision coverage, or provide for those needs some other way. What the court has discretion over is the mechanism, not whether the child is covered. Where the paying parent carries the coverage, the other parent’s share is credited against the support payment.
- Uninsured medical costs are discretionary. Section 505(a)(4)(B) says the court “may order either or both parents to contribute to the reasonable health care needs of the child not covered by insurance” — unreimbursed medical, dental, orthodontic, or vision expenses, and prescriptions not covered by the policy.
- There is a ceiling on what counts as “reasonable” coverage cost. Under § 505(a)(4)(G), “a reasonable cost for providing health insurance coverage for the child may not exceed 5% of the providing parent’s gross income.” A parent receiving a credit for carrying the coverage also has to submit annual proof that the child is still covered.
- Employment-related child care — § 505(a)(3.7) lets the court order either or both parents to contribute to reasonable child care expenses. Actual expenses are used where available and may be averaged over the most recent 12 months where they vary. A parent whose child care costs change must notify the other party within 14 days where the change would affect the annualized amount in the order.
- School and extracurricular expenses — § 505(a)(3.6) gives the court discretion to order contribution to reasonable expenses “intended to enhance the educational, athletic, social, or cultural development of the child.”
Because these are usually ordered as a percentage split rather than folded into one number, they are also the most common source of post-judgment arguments. Spell out in the order who pays what, to whom, and by when.
When Support Ends — and What Comes After
For child support purposes, § 505 defines “child” as any child under 18, and any child over 18 who has not yet turned 19 and is still attending high school. So support does not simply stop on an eighteenth birthday mid-senior-year.
Your order should already say when it ends. Section 505(g) requires that “an order for support shall include a date on which the current support obligation terminates,” and that the date be no earlier than the child’s eighteenth birthday — or, where the child will not graduate high school until after turning 18, no earlier than the earlier of graduation or the child’s nineteenth birthday. So the first place to look is the order itself, not a birthday.
Two things people routinely get wrong about that date. First, the statute requires the order to state “that the termination date does not apply to any arrearage that may remain unpaid on that date” — reaching the end date does not erase what is already owed, and arrears stay enforceable. Second, the termination date does not lock the court out: nothing in the subsection prevents the court from modifying or terminating the order if the child is otherwise emancipated.
College is a separate question with a separate statute. Basic child support ends, but 750 ILCS 5/513 gives the court authority to allocate a non-minor child’s educational expenses between the parents. Separately, 750 ILCS 5/513.5 allows the court to award support for a non-minor child with a disability where the statutory conditions are met — so the age rule is not the end of the analysis in every family. Both are distinct forms of relief rather than an automatic continuation of basic support; how and when each is raised depends on where your case stands, which is worth asking about before the support order terminates.
When Courts Deviate, and How Support Gets Modified Later
Deviation. Section 505(a)(3.4) makes the guideline figure a rebuttable presumption. The court “may deviate from the child support guidelines if the application would be inequitable, unjust, or inappropriate” — and if it does, the paperwork requirement is strict:
“Any deviation from the guidelines shall be accompanied by written findings by the court specifying the reasons for the deviation and the presumed amount under the child support guidelines without a deviation.”
The order must show both the guideline number and why the court departed from it. Reasons the statute contemplates include extraordinary medical expenditures needed to preserve the life or health of a party or child, and additional expenses tied to a child’s needs.
Modification. Under 750 ILCS 5/510 a support order can be modified on a substantial change in circumstances — a genuine job loss, a significant income change, or a real change in the allocation of parenting time. There is also a streamlined route for cases receiving state child support services: after a set interval, an order may be reviewed without proving a substantial change, where the guidelines would now produce a materially different figure.
The single most costly mistake in this area: a modification reaches only installments accruing after the moving party gives due notice of the filing — so it is filing and getting notice properly served that protects you, not the day you decided to act. A court will not retroactively erase support that accrued while you waited. Every month of delay is a month you still owe at the old rate, and unpaid support accrues statutory interest. If your circumstances have genuinely changed, file promptly, serve properly, and negotiate afterward. Our post-judgment page covers that process.
Frequently Asked Questions About Illinois Child Support
Is Illinois child support still 20% of net income for one child? No. Those flat percentages were replaced on July 1, 2017 by Public Act 99-764. Illinois now uses income shares, which starts from both parents’ net incomes. A number produced by the old percentages is not an estimate — it is the wrong calculation.
If we split parenting time 50/50, does anyone pay child support? Usually yes. Once each parent has 146 or more overnights, § 505(a)(3.8) multiplies the basic obligation by 1.5 and cross-credits each parent’s share against the other’s parenting time. Where incomes differ, that offset almost always leaves one parent paying — sometimes the parent with slightly more overnights, as the example above shows.
Does the court use my gross pay or my take-home pay? Neither exactly. It uses a statutory “net income,” normally derived from your gross income through the HFS conversion table using standardized tax amounts. Your actual paycheck deductions — a 401(k) contribution, for instance — do not automatically reduce it.
How are overnights counted? This is worth pinning down early rather than assuming. Because 146 is an exact threshold with a large financial consequence on either side of it, the schedule in your parenting plan should be drafted so the annual count is unambiguous — including holidays, school breaks, and summer — instead of being argued about after the fact. Confirm the counting convention being applied to your case before you agree to a schedule.
What if the other parent quit a good job to lower support? The court can impute income based on earning capacity rather than accept the reduced figure, but it must make written findings identifying the basis for the amount. Bring evidence of work history and what the local market pays.
When does child support end in Illinois? Check your order first — § 505(g) requires it to state a termination date. That date is no earlier than the child’s eighteenth birthday, or, if the child is still in high school then, no earlier than the earlier of graduation or age 19. Two exceptions matter: reaching the date does not wipe out unpaid arrears, and under 750 ILCS 5/513.5 a court may award support for a non-minor child with a disability. College expenses are handled separately under 750 ILCS 5/513.
Talk Through Your Numbers With a Lake County Child Support Attorney
Most people arrive at this with a figure someone gave them and no idea whether it is right. Often it is not — either because it came from the pre-2017 percentages, because it was run on a stale conversion table, or because the parenting schedule was never plugged in.
I have spent more than 20 years handling family law matters in Lake County, and running the actual arithmetic on your real income and your real parenting schedule is usually the fastest way to turn a stressful unknown into a decision you can make. That is also true if you already have an order and your circumstances have changed — the calculation tells you whether a modification is worth filing, and filing promptly is what protects you.
Reaching an agreement is generally faster, cheaper, and leaves the two of you in control of the outcome rather than a judge. Getting the numbers right first is what makes that possible.
For a confidential initial consultation, call (847) 623-4002 or contact the office. You can also read more about child support, allocation of parental responsibilities and parenting time, or post-judgment modifications. Cases in Lake County are heard in the 19th Judicial Circuit, at the courthouse in Waukegan; the office is in Gurnee.
This article is general legal information, not legal advice, and does not create an attorney-client relationship. Illinois law changes and every case turns on its specific facts. Consult a licensed Illinois family-law attorney about your situation.
Primary sources: 750 ILCS 5/505 (income shares, shared physical care, deviation, minimum orders); 750 ILCS 5/510 (modification); 750 ILCS 5/513 and 5/513.5 (non-minor children); Illinois HFS Income Shares tables, effective March 20, 2026.
