Parents who are divorcing, separating, or establishing parentage frequently have questions about how much child support will be ordered. Illinois does not calculate support solely from the paying parent’s income. Instead, courts use an income shares model that considers the financial resources of both parents, the number of children covered by the order, and the amount of parenting time exercised in certain cases.
The basic idea is that children should receive approximately the same proportion of their parents’ combined income that would have been available if the parents lived together. Rather than assigning the entire support obligation to one parent without considering the other parent’s income, the model estimates the total amount both parents would ordinarily spend on their children and then allocates that obligation between them.
Illinois child support calculations can still become complicated, particularly when a parent owns a business, receives bonuses or commissions, is voluntarily unemployed, supports children from another relationship, or exercises a substantial number of annual overnights. Understanding the basic calculation can help parents prepare for a divorce, parentage case, or child support modification.
Illinois previously relied more heavily on a percentage of the paying parent’s income. Under the current income shares system, both parents’ net incomes are included in the analysis.
The model recognizes that both parents have an ongoing duty to support their children. In a household where the parents live together, their incomes are generally combined to pay for housing, food, clothing, transportation, school expenses, healthcare, and other costs. When the parents live separately, the children should continue to benefit from both parents’ financial resources.
Illinois uses a Schedule of Basic Child Support Obligations to estimate the amount that parents with a particular combined net income would spend on their children. The schedule provides different amounts depending on whether the order covers one, two, three, four, five, or six children.
The Illinois Department of Healthcare and Family Services updates both the schedule and the gross-to-net income conversion table. The current tables became effective March 20, 2026, and Illinois now updates these materials annually to reflect changing economic conditions.
Although every case has its own facts, an income shares calculation generally involves several steps.
The court begins by identifying each parent’s gross income.
Gross income is broadly defined and may include income from sources such as:
The court is not limited to the amount shown on a parent’s most recent paycheck. It may review tax returns, pay records, bank statements, business documents, and other financial evidence to determine the parent’s actual income.
Certain payments or benefits may be excluded from gross income under Illinois law. Because the treatment of income can depend on its source, parents should not assume that every payment they receive will be included or excluded.
Illinois child support is based primarily on net income rather than gross income.
Parents may use one of two methods to determine net income:
Under the standardized method, the court applies the official Illinois gross-to-net income conversion table. The table estimates federal and state taxes and other standardized deductions based on gross income.
Under the individualized method, actual tax obligations and authorized deductions may be used when reliable documentation is available. This approach may be relevant when a parent’s tax circumstances differ substantially from the standardized assumptions.
Net income may also be adjusted for certain prior support obligations or legally recognized deductions. The court must determine which method and deductions are appropriate under the circumstances.
Once the court determines each parent’s adjusted net income, those amounts are added together.
For example, assume one parent has a monthly adjusted net income of $6,000 and the other has a monthly adjusted net income of $4,000. Their combined monthly net income would be $10,000.
The first parent earns 60% of the combined net income, while the second earns 40%.
Those percentages are important because they are used to divide the basic child support obligation between the parents.
The court then locates the parents’ combined adjusted net income on the Illinois Schedule of Basic Child Support Obligations.
The schedule identifies an estimated monthly support amount based on:
Suppose the schedule shows that parents with a combined monthly net income of $10,000 have a basic support obligation of $2,100 for two children. That $2,100 represents the combined estimated obligation of both parents—not necessarily the amount one parent must pay to the other.
The Illinois schedule is based on economic data concerning the typical costs of raising children in families with comparable income.
Each parent is assigned a percentage of the basic obligation corresponding to that parent’s percentage of the combined net income.
Using the example above:
Parent One’s share would be $1,260, and Parent Two’s share would be $840.
In a traditional parenting arrangement, the parent receiving support is presumed to spend that parent’s share directly on the children. The other parent generally pays the allocated amount through the child support order.
The calculation may change when the parents have a shared-care parenting arrangement.
Parenting time does not always change the basic support calculation. A special shared-care formula applies when each parent has at least 146 overnights with the child during the year.
The 146-overnight threshold represents 40% of the annual overnights.
When shared care applies, Illinois multiplies the basic child support obligation by 1.5. This adjustment recognizes that both parents maintain homes and incur duplicated expenses for the children, including housing, food, utilities, clothing, and transportation.
The court then:
Illinois law specifically provides that the 1.5 multiplier and shared-care formula apply when each parent has 146 or more annual overnights.
Shared parenting does not automatically eliminate child support. Even when parents divide overnights equally, one parent may still pay support if there is a meaningful income difference.
Some families have what Illinois law describes as a split-care arrangement. This can occur when each parent has the majority of parenting time with at least one child.
For example, one child may primarily live with Parent One while another primarily lives with Parent Two. In that situation, the court may calculate each parent’s obligation for the child or children primarily residing with the other parent and offset the two obligations.
These calculations can become more complex when shared care and split care overlap or when children follow substantially different schedules.
The basic obligation does not necessarily cover every expense associated with raising a child.
Illinois courts may allocate additional expenses between the parents, often in proportion to their respective net incomes. These expenses may include:
The court may require one or both parents to provide health insurance for the child when coverage is available at a reasonable cost. The portion of the insurance premium attributable to the child may be included in the calculation.
Parents may be required to share deductibles, copayments, dental care, orthodontic treatment, therapy, prescriptions, vision care, and other reasonable healthcare expenses not paid by insurance.
Work-related childcare expenses may be added to the support calculation. These can include daycare, before-school care, after-school care, babysitting, or summer care required because a parent is working or pursuing qualifying education.
The court may order parents to contribute to reasonable school expenses and extracurricular activities intended to support the child’s educational, athletic, social, or cultural development.
These expenses are not always divided equally. The allocation may depend on income, the nature of the expense, the child’s needs, and the terms of the parenting plan.
A parent cannot always reduce a child support obligation simply by choosing not to work or by accepting substantially lower-paying employment.
When the court finds that a parent is voluntarily unemployed or underemployed, it may impute income. This means the court assigns an income amount based on evidence such as:
Income should not be imputed automatically. The court must consider the reasons for the employment situation and the available evidence.
Incarceration is not treated as voluntary unemployment under current Illinois law. A parent who has no gross income and cannot work because of incarceration may also qualify for a rebuttable presumption of a zero-dollar order.
Self-employment income often requires closer review because a business owner may control how income and expenses are reported.
The court may examine:
A deduction that is legitimate for tax purposes is not automatically an allowable deduction when calculating child support. The court may add back expenses that reduce taxable income but provide a personal benefit or are unnecessary for producing income.
Forensic accounting or business valuation assistance may be appropriate in cases involving closely held businesses or disputed self-employment income.
Yes. The income shares amount is the presumptive guideline obligation, but a court may deviate when applying the guidelines would be inappropriate, unjust, or contrary to the child’s best interests.
Relevant circumstances may include:
When a court deviates, it generally must explain the guideline amount, the amount actually ordered, and the reasons for the deviation.
A parent seeking a deviation should present detailed financial evidence rather than simply arguing that the guideline amount feels unfair.
The Illinois Department of Healthcare and Family Services provides an online Child Support Estimator. The estimator uses the information entered by the user to generate an estimated guideline amount.
The estimator can be helpful for preliminary planning, but it is not a substitute for a court order or individualized legal analysis. Its result depends on the accuracy of the income, deductions, parenting time, insurance, and expense information entered.
The estimator may not fully address disputed self-employment income, imputed income, unusual tax circumstances, deviations, fluctuating compensation, or complex parenting arrangements.
A child support order may be modified when the statutory requirements are satisfied.
Common reasons for requesting modification include:
An income change does not automatically modify the order. The existing amount generally remains enforceable until a court or authorized administrative process changes it.
Because retroactive modification is limited, a parent experiencing a substantial change should act promptly.
Not always, but the higher-earning parent frequently has the larger allocated obligation. Parenting time, add-on expenses, prior support obligations, and other factors may affect the final amount.
No. Equal parenting time does not automatically eliminate support. The shared-care formula considers both income and overnights, so a parent with substantially greater income may still owe support.
A new spouse generally does not have a legal duty to support the child and that spouse’s income is not simply added to the parent’s income. However, the household’s financial circumstances may become relevant in limited situations involving deviations or claims about actual expenses.
They may be. Recurring bonuses, commissions, overtime, and other variable compensation can be included in gross income. The court may average fluctuating income or establish a percentage-based obligation for additional compensation.
The regular child support calculation generally addresses minor children. Illinois courts may separately order contributions toward educational expenses for a non-minor child under Section 513 of the Illinois Marriage and Dissolution of Marriage Act.
Although Illinois uses a standardized income shares model, the final calculation depends on accurate income information, authorized deductions, the parenting schedule, health insurance, childcare costs, and the child’s specific needs.
Disputes over self-employment income, bonuses, hidden compensation, voluntary unemployment, or shared parenting can significantly affect the result. An incorrect calculation may create financial consequences that continue for years.
Gordon & Perlut, LLC represents parents throughout Chicago, Skokie, Cook County, and surrounding Illinois communities in child support establishment, modification, enforcement, parentage, and divorce proceedings.
Contact Gordon & Perlut, LLC at our Chicago office at 312-360-0250 or call our Skokie office at 847-329-0101 to speak with an experienced Chicago child support lawyer about how the Illinois income shares model may apply to your family.
This article provides general information about Illinois law and does not constitute legal advice for any individual matter.
