Child support in Illinois generally continues until the child turns 18 or graduates from high school, whichever is later. In some cases, support may be extended beyond these limits, such as when the child has special needs or requires support for post-secondary education.

Illinois uses an Income Shares Model for calculating child support, which was implemented in 2017. This model is based on the principle that a child should receive the same proportion of parental income as if both parents were still living in an intact household. The method takes into account both parents’ combined net income and amount of parenting time to determine the appropriate level of support, which is then divided between the parents, thus resulting in one parent paying the other.

The Illinois Department of Healthcare and Family Services (HFS) provides guidelines, including a worksheet and schedule of basic child support obligations, to help calculate the correct amount of child support. The key steps involved in calculating child support include:

1. Determine Each Parent's Net Income: The court calculates each parent’s monthly net income by subtracting deductions like taxes, health insurance premiums, and mandatory retirement contributions from their gross income.

2. Combine Monthly Net Income: The court adds both parents' net incomes to determine their combined monthly net income.

3. Reference the Schedule of Basic Child Support Obligations: Based on the combined monthly net income and the number of children, the court refers to a schedule that estimates the amount of child support that should be allocated.

4. Calculate Each Parent's Share: The court then allocates the total child support obligation between the parents, according to their percentage share of the combined income.

5. Adjustments for Parenting Time: If the non-custodial parent (the obligor) has substantial parenting time (defined as 146 or more overnights per year), the court may reduce their child support obligation, considering the direct expenses incurred during this time.

While the Income Shares Model provides a framework for determining child support, the court can deviate the calculated amount if the application of guidelines would be inequitable, unjust, or inappropriate. These include:

1. The Financial Resources of the Child: If the child has independent income or assets (such as a trust or inheritance), this may reduce the amount of support required from the parents.

2. The Financial Resources and Needs of Both Parents: The court considers the parents' ability to pay child support, including their income, necessary living expenses, and any other financial obligations they may have.

3. The Standard of Living the Child Would Have Enjoyed: The court aims to maintain the child’s standard of living as close as possible to what they would have experienced if the family unit had remained intact.

4. The Child's Physical and Emotional Health and Educational Needs: The court takes into account any special needs of the child, including medical conditions or disabilities, as well as the costs of educational expenses (e.g., tuition, tutoring).

In addition to the basic child support obligation, Illinois courts may order parents to contribute to other expenses related to the child’s well-being, such as:

1. Healthcare Expenses: 

• Courts can require one or both parents to provide health, dental, or vision insurance for the child. If neither parent has access to affordable private insurance, the court may order that one parent enroll the child in public health insurance programs, such as Medicaid, and that both parents contribute to the costs.

• Uninsured medical expenses, such as co-pays, prescriptions, dental work, and orthodontic care, are typically divided between the parents based on their respective incomes.

2. Childcare Costs: 

• If childcare is necessary to allow the custodial parent to work or attend school, these expenses are factored into the child support order. The court will prorate childcare costs based on each parent's share of the combined net income.

• Childcare costs can include before- and after-school programs, daycare, or summer camps.

3. Extracurricular and Educational Expenses:

• The court may order parents to contribute to reasonable extracurricular activities, school fees, or special educational programs designed to enhance the child's development.

•  Costs for private school or college tuition may also be considered, depending on the financial circumstances of the parents and the child's educational needs.

Illinois courts have various methods for enforcing child support orders. If a parent fails to pay child support, the court may take action to ensure compliance, including:

1. Income Withholding: Child support payments can be automatically deducted from the obligor’s wages through their employer. This is the most common enforcement method.

2. Contempt of Court: If a parent is found in contempt for failing to pay child support, they may face penalties, including fines, probation, or even imprisonment for up to six months.

3. License Suspension: The court can suspend the obligor’s driver’s license or professional licenses if they are more than 90 days behind on payments.

4. Seizure of Assets: The court can place liens on the obligor’s property, intercept tax refunds, or garnish bank accounts to collect unpaid child support.

5. Accrual of Interest: Child support arrears accrue interest at the rate specified in Illinois law, adding to the amount owed by the delinquent parent.