Co-Parenting Expense Rules in Illinois (2026)

How Illinois Handles Shared Child Expenses

Illinois uses an income-shares model for child support, which means both parents' incomes are combined to determine a total support obligation, and each parent is responsible for their proportional share. This approach replaced the old flat-percentage formula in 2017 and is designed to approximate what the parents would have spent on the child had the household remained intact.

On top of basic child support, Illinois law provides a second layer of expense sharing under 750 ILCS 5/513 — the Section 513 contribution statute. This section covers additional expenses like childcare, education, extracurricular activities, and health care costs that fall outside the basic support calculation. These additional costs are divided between parents based on each parent's percentage share of their combined income.

Understanding the distinction between expenses covered by basic support and expenses governed by Section 513 is essential. If an expense is already factored into the basic support order, you generally cannot seek additional reimbursement. But if the expense qualifies under Section 513 or the health care provisions in Section 505.2, your co-parent has a legal obligation to contribute their proportional share.

What Basic Child Support Covers (750 ILCS 5/505)

The Illinois Marriage and Dissolution of Marriage Act, codified at 750 ILCS 5/505, governs how basic child support is calculated. Under the income-shares model, the court determines each parent's net income, combines them into a single figure, and then consults a statutory schedule of basic child support obligations based on the combined net income and the number of children.

The resulting total obligation represents the amount that an intact family with the same combined income would typically spend on raising their children. This covers the child's fundamental living expenses:

• Housing — the child's share of rent or mortgage, utilities, and household maintenance
• Food — grocery costs and everyday meals
• Clothing — routine clothing purchases and seasonal wardrobe needs
• Basic transportation — the cost of getting the child to school, medical appointments, and daily activities
• Ordinary educational expenses — standard school supplies, fees, and materials required by public schools
• Routine entertainment — age-appropriate toys, books, and everyday recreation

Once the total obligation is determined from the schedule, each parent's share is calculated based on their percentage of the combined net income. The parent with less parenting time (the non-custodial parent) typically pays their share directly to the other parent. The parent with more parenting time (the custodial parent) is presumed to spend their share directly on the child during their parenting time.

How Net Income Is Calculated

Illinois defines net income broadly under Section 505(a)(3). It starts with gross income from all sources — wages, salary, commissions, bonuses, investment income, Social Security benefits, pensions, annuities, trusts, and self-employment income. Certain deductions are then applied:

• Federal and state income taxes (based on actual filing status)
• Social Security and Medicare contributions (FICA)
• Mandatory retirement contributions
• Union dues
• Health insurance premiums for the parent (not the child — that is handled separately)
• Prior child support or maintenance obligations actually being paid

The resulting figure is each parent's net income for purposes of the child support calculation. Illinois courts may also impute income to a parent who is voluntarily unemployed or underemployed, meaning the court can assign an income figure based on what that parent could reasonably be earning given their education, skills, and work history.

The Parenting Time Adjustment

Illinois applies a shared parenting adjustment when the non-custodial parent has the child for 146 or more overnights per year. This is sometimes called the "shared care" or "40% rule" because 146 overnights equals approximately 40% of the year. When shared parenting applies, the basic child support obligation is adjusted using a statutory formula that accounts for the increased expenses incurred by the parent with more overnights and the decreased expenses of the other parent. This adjustment reduces the net transfer amount but does not eliminate the obligation.

Additional Expenses Under Section 513 (750 ILCS 5/513)

Section 513 of the Illinois Marriage and Dissolution of Marriage Act is the key statute for expenses that go beyond basic child support. It authorizes courts to order either or both parents to contribute to specific categories of additional child-related costs. These expenses are divided in proportion to each parent's percentage share of combined net income — the same ratio used for basic support.

Childcare Expenses

Section 513 covers childcare costs that are necessary because a parent is employed, seeking employment, or attending an educational or vocational training program. This includes:

• Daycare and pre-school tuition
• Before-school and after-school care programs
• Summer childcare during school breaks
• Babysitting costs directly related to work schedules

The childcare expense must be reasonable and necessary. If one parent chooses a premium childcare option that significantly exceeds the cost of comparable alternatives in the area, the court may limit the shared obligation to the cost of a reasonable alternative.

Educational Expenses

Courts may order parents to contribute to educational costs beyond what is covered by basic support. Section 513 educational expenses commonly include:

• Private school tuition — if the child was already enrolled before the divorce or if both parents agree, courts frequently order shared payment of private school costs
• Tutoring — when a child has documented academic needs that require outside help
• Special education costs — services, therapies, or programs beyond what the school district provides
• College-preparatory programs — ACT/SAT preparation, application fees, and related costs for older children

For private school tuition, Illinois courts look at factors such as the child's history of attending private school, the quality of available public school alternatives, each parent's ability to contribute, and whether the expense is in the child's best interest. A parent cannot unilaterally enroll a child in private school and expect the other parent to pay half without either agreement or a court order.

Illinois also has a separate provision under 750 ILCS 5/513(a)(2) that allows courts to order contribution to a child's post-secondary (college) education expenses, including tuition, fees, housing, books, and living costs. This is relatively unusual among U.S. states — many states do not require parents to contribute to college costs. In Illinois, the court considers the financial resources of both parents and the child, the standard of living the child would have enjoyed had the family remained intact, and the child's academic performance.

Extracurricular Activities

Extracurricular activity costs — sports leagues, music lessons, art classes, drama programs, camps, and similar enrichment activities — fall under Section 513 as well. Courts in Illinois evaluate several factors before ordering parents to share these costs:

• The child's established participation — if the child was already involved in the activity before the separation, courts are more likely to order continued shared funding
• The reasonableness of the expense — a $200/season recreational soccer league is treated very differently from a $10,000/year competitive travel team
• Each parent's financial ability — courts will not order a parent to contribute to extracurricular costs they genuinely cannot afford
• The child's best interest — whether the activity supports the child's physical, social, emotional, or educational development

Both parents must contribute to court-ordered extracurricular expenses based on their income share. If the expense was not court-ordered and the parents did not agree to it, the parent who incurred the cost may not be able to recover the other parent's share.

Best practice: Before enrolling your child in a new activity, send your co-parent a written message (text or email) that specifies the activity, the cost, and each parent's estimated share. For example: "I would like to sign Jordan up for travel basketball — the season costs $800 total. Based on our income split (60/40), your share would be $320 and mine would be $480. Do you agree?" This written record protects both parents if a dispute arises later.

Health Care Expenses (750 ILCS 5/505.2)

Health care expenses for children in Illinois are governed by Section 505.2 of the IMDMA, which establishes detailed rules about insurance coverage and the allocation of unreimbursed medical costs.

Health Insurance Coverage

Under Section 505.2, the court must determine which parent can obtain health insurance coverage for the child at a reasonable cost. Illinois defines "reasonable cost" as not exceeding 5% of the parent's net income. If both parents have access to affordable coverage, the court designates one parent to carry the insurance and may allocate the premium cost as part of the overall support calculation.

The cost of the child's health insurance premium is typically added to the basic child support obligation before the proportional split is applied. This means both parents effectively share the premium cost based on their income percentages.

Unreimbursed Medical Expenses

Unreimbursed medical expenses — deductibles, co-pays, coinsurance, and any treatment or service not covered by insurance — are shared between parents in proportion to their net incomes. This includes:

• Doctor visit co-pays — routine well-child visits, sick visits, specialist consultations
• Prescription medications — co-pays and costs for medications not covered by insurance
• Dental and orthodontic costs — cleanings, fillings, braces, retainers, and oral surgery
• Vision care — eye exams, glasses, contact lenses
• Mental health services — therapy, counseling, psychiatric evaluations, and medication management
• Emergency room visits — co-pays and deductible amounts
• Physical therapy and rehabilitation — prescribed treatment for injuries or developmental needs

Illinois courts generally require the parent who incurs the unreimbursed medical expense to provide the other parent with documentation (receipt, explanation of benefits from the insurer, and proof of payment) within 30 days of receiving the bill or paying the expense. The other parent then has 30 days from receiving the documentation to reimburse their proportional share.

These timelines may vary based on the specific language in your court order or marital settlement agreement. Always check your order for the exact reimbursement procedures and deadlines.

Emergency vs. Non-Emergency Medical Decisions

For emergency medical care, either parent can authorize treatment without consulting the other. The expense is then shared based on income proportions regardless of prior agreement.

For non-emergency medical decisions — elective procedures, orthodontic treatment, therapy, or non-urgent specialist consultations — Illinois law generally expects parents to confer before incurring significant costs. If parents disagree about a non-emergency medical expense, the parent seeking the treatment may need to obtain a court order before the other parent is obligated to share the cost. However, if the expense is deemed medically necessary by a licensed provider, courts routinely order both parents to contribute.

Extracurricular Activities: A Deeper Look

Because extracurricular expenses are one of the most common sources of conflict between co-parents in Illinois, it is worth examining how courts approach these costs in more detail.

The Reasonable Necessity Test

Illinois courts apply what practitioners call a "reasonable necessity test" when deciding whether to order shared funding for an extracurricular activity. The court considers:

1. Is the activity beneficial to the child? Courts favor activities that support physical health, social development, talent cultivation, or academic enrichment.
2. Is the cost reasonable relative to the family's means? A family with a combined income of $100,000 is unlikely to be ordered to share the cost of a $15,000 elite sports program. The same family might reasonably be expected to share a $500 seasonal league fee.
3. Was the child already participating? Continuity matters. Courts are reluctant to disrupt a child's established activities and social connections because of parental conflict.
4. Do both parents support the activity? While mutual agreement is not strictly required (a court can order contribution over one parent's objection), courts are more likely to order shared costs when both parents recognize the activity's value.

When One Parent Objects

If one parent objects to the cost of an extracurricular activity and the expense is not already covered by a court order, the objecting parent is generally not required to contribute until a court rules otherwise. The parent who wants the child to participate has two options:

• Pay the full cost themselves and forgo reimbursement, or
• File a petition asking the court to order both parents to contribute under Section 513

Courts typically rule in favor of ordering shared contribution when the activity is established, reasonably priced, and beneficial to the child. The burden is on the requesting parent to demonstrate these factors.

Practical Calculation Example

Let us walk through a detailed example to show how Illinois child support and additional expense sharing work in practice.

The Facts

• Parent A earns $85,000 per year gross, with a net income of approximately $62,000 after taxes and mandatory deductions
• Parent B earns $55,000 per year gross, with a net income of approximately $42,000 after taxes and mandatory deductions
• Combined net income: $104,000
• One child, age 8
• Parent A has the child 60% of overnights (219 nights); Parent B has 40% (146 nights)
• The child plays recreational soccer, takes piano lessons, and needs orthodontic treatment

Step 1: Calculate Each Parent's Income Share

• Parent A's share: $62,000 / $104,000 = 59.6% (approximately 60%)
• Parent B's share: $42,000 / $104,000 = 40.4% (approximately 40%)

Step 2: Determine Basic Child Support

Using the Illinois Schedule of Basic Child Support Obligations (the statutory table in Section 505), a combined net income of $104,000 for one child produces a basic child support obligation of approximately $1,095 per month (this figure comes from the schedule; actual amounts depend on the specific table in effect).

• Parent A's share of basic support: $1,095 x 60% = $657/month
• Parent B's share of basic support: $1,095 x 40% = $438/month

Because Parent A has the majority of overnights, Parent B would pay their $438 share to Parent A. Parent A is presumed to spend their $657 share directly during their parenting time. (If the shared parenting adjustment applies due to Parent B's 146 overnights, the net transfer amount may be reduced, but both parents still owe their proportional share.)

Step 3: Allocate Health Insurance Costs

Assume Parent A carries health insurance for the child at a cost of $200/month for the child's coverage. This is added to the basic obligation and shared proportionally:

• Parent A's share of insurance: $200 x 60% = $120/month
• Parent B's share of insurance: $200 x 40% = $80/month

Since Parent A already pays the $200 premium directly, Parent B owes an additional $80/month to reimburse Parent A for their share.

Step 4: Divide Section 513 Additional Expenses

Now apply the 60/40 income split to monthly additional expenses:

Step 5: Determine the Net Monthly Transfer

Putting it all together, Parent B's total monthly obligation to Parent A includes:

• Basic child support transfer: $438
• Health insurance reimbursement: $80
• Section 513 expense share (assuming Parent A pays upfront): $360
• Total monthly transfer from Parent B to Parent A: approximately $878

This example illustrates why tracking additional expenses separately from basic support is so important. The Section 513 costs ($360/month) represent a significant amount on top of basic support, and without clear documentation, disputes over these amounts become inevitable.

The 2017 Reform: From Flat Percentage to Income-Shares

Understanding the 2017 reform is important for any Illinois co-parent, especially if your original court order predates the change.

The Old System (Before July 1, 2017)

Before 2017, Illinois used a flat percentage model for child support. The non-custodial parent paid a fixed percentage of their net income based on the number of children:

• 1 child: 20% of net income
• 2 children: 28% of net income
• 3 children: 32% of net income
• 4 children: 40% of net income
• 5 children: 45% of net income
• 6 or more children: 50% of net income

This system had significant drawbacks. It only considered one parent's income, meaning a non-custodial parent earning $60,000 paid the same percentage whether the custodial parent earned $20,000 or $200,000. It also did not account for the amount of parenting time each parent had with the child.

The New System (After July 1, 2017)

Public Act 99-0764, effective July 1, 2017, replaced the flat percentage model with the income-shares model codified in the revised Section 505. The key changes were:

• Both parents' incomes are considered — the total obligation is based on combined net income, not just one parent's earnings
• A statutory schedule sets the obligation — based on extensive economic data about what families actually spend on children at various income levels
• Parenting time affects the calculation — the shared parenting adjustment (146+ overnights) reduces the net transfer amount to reflect the non-custodial parent's direct spending during their time with the child
• Health insurance and childcare are integrated — these costs are added to the basic obligation and shared proportionally, rather than handled as separate add-ons

What This Means for Existing Orders

If your child support order was entered before July 1, 2017, it was calculated under the old flat percentage system. Your order remains in effect until it is modified, but either parent can petition for modification under 750 ILCS 5/510. Courts will apply the income-shares model to any modification.

The 2017 reform generally results in different (not necessarily higher or lower) support amounts compared to the old system. For families where the custodial parent earns significantly more than the non-custodial parent, the new model may reduce the non-custodial parent's obligation. For families where one parent has substantially more parenting time and the incomes are more equal, the results can vary.

Documentation and Tracking Requirements

Illinois courts expect parents to maintain accurate, organized records of shared child expenses. When disputes arise — and they often do — the parent with thorough documentation holds a significant advantage. Here is what you should be tracking:

What to Keep

• Receipts and invoices for every expense that falls under Section 513 or Section 505.2 — childcare bills, medical co-pays, activity registration fees, tuition invoices, dental statements
• Explanation of Benefits (EOB) statements from your health insurer showing what was covered and what remains unreimbursed
• Proof of payment — bank statements, credit card records, or canceled checks showing you actually paid the expense
• Written communication with your co-parent about shared expenses — texts, emails, or messages through a co-parenting app documenting agreement (or disagreement) on specific costs
• Court orders and agreements — your complete marital settlement agreement, child support order, and any subsequent modifications specifying how expenses are to be shared

Reimbursement Procedures

Most Illinois court orders specify a reimbursement process. A typical framework works like this:

1. Parent A incurs a Section 513 expense and pays it
2. Parent A sends Parent B documentation within 30 days — typically the receipt, any insurance EOB, and a calculation of Parent B's share
3. Parent B reimburses their share within 30 days of receiving the documentation
4. If Parent B disputes the expense, they must raise the objection promptly and in writing

If your court order does not specify reimbursement timelines, follow the 30-day standard used in most Illinois counties and document your compliance carefully.

Why Tracking Matters

Over the course of a year, Section 513 expenses can add up to thousands of dollars. Without a systematic way to track who paid what and who owes whom, small discrepancies compound into major disputes. A $40 co-pay here, a $75 league fee there, a $200 dental bill — by month six, neither parent can confidently say who owes what without organized records.

This is precisely the problem that purpose-built expense tracking tools solve. Spreadsheets work for the first few months, but they break down when you need to send reimbursement requests, attach receipts, and maintain a running balance over years of co-parenting.

When You Disagree: Mediation and Modification

Disagreements about child expenses are common, even among co-parents with a generally cooperative relationship. Illinois law provides structured pathways for resolving these disputes.

Informal Resolution

Start with direct, written communication. Many expense disagreements arise from misunderstandings rather than genuine conflicts. Send your co-parent a clear, factual message that includes:

• The specific expense and the amount
• Documentation (receipt, invoice, or EOB)
• The statute or court order provision that requires shared payment
• A calculation of each parent's share based on income proportions
• A reasonable deadline for reimbursement

Avoid accusatory language. Frame the request around the child's needs and the existing legal framework.

Mediation

If informal communication fails, Illinois strongly encourages mediation before court intervention. Under 750 ILCS 5/404.5, courts may order parents to participate in mediation for disputes related to custody, support, or expense allocation. Many Illinois counties have court-connected mediation programs that offer free or low-cost services.

Mediation is often faster, less expensive, and less adversarial than litigation. A trained mediator helps both parents identify the underlying concerns and negotiate a workable agreement. Mediated agreements can be submitted to the court for approval and, once approved, become enforceable court orders.

Modification Under 750 ILCS 5/510

If your circumstances have changed significantly since your last support order, you can petition for a modification under Section 510. Illinois allows modification of child support orders when there has been a substantial change in circumstances. Common grounds for modification include:

• A significant change in either parent's income — job loss, promotion, career change, disability
• A change in the child's needs — new medical conditions, educational requirements, or activity costs
• A change in parenting time — if the overnights split has shifted substantially
• The passage of time — Illinois law creates a rebuttable presumption that a modification is warranted if applying the current guidelines would result in a change of 20% or more from the existing order (Section 510(a)(2)(B))

To request a modification, you file a Petition to Modify Child Support with the court that issued the original order. You must demonstrate the substantial change in circumstances and provide updated financial information for both parents. The court will recalculate support using the current income-shares formula.

Enforcement

If your co-parent refuses to pay their share of expenses despite a valid court order, Illinois provides several enforcement mechanisms:

• Income withholding — the court can order that the obligor's employer deduct child support directly from their paycheck under 750 ILCS 28/20
• Contempt of court — willful failure to pay court-ordered support can result in fines or even incarceration
• Liens and asset seizure — the Illinois Department of Healthcare and Family Services (HFS) can place liens on property, intercept tax refunds, suspend driver's licenses, and pursue other collection methods
• Interest on arrears — unpaid child support accrues interest at the statutory rate of 9% per year under 750 ILCS 5/505(b)

Key Statutes and Resources

• 750 ILCS 5/505 — Child Support; Determinations — The core child support statute establishing the income-shares model, net income definitions, and the basic support obligation schedule
• 750 ILCS 5/505.2 — Health Care Expenses — Rules for health insurance coverage, premium allocation, and unreimbursed medical expense sharing
• 750 ILCS 5/510 — Modification and Termination — Standards and procedures for modifying child support orders
• 750 ILCS 5/513 — Contribution to Child Expenses — Additional expense categories (childcare, education, extracurriculars) and the pro-rata income sharing rule
• Illinois Child Support Estimator — Free online tool from the Illinois Department of Healthcare and Family Services for estimating child support under the income-shares model
• Illinois Legal Aid Online — Child Support — Free legal information and resources for Illinois parents navigating child support