Illinois uses the Income Shares model — both parents’ net incomes are combined. Updated for 2026 — covers 50/50 custody, arrears, modifications and Illinois child support laws.
BothParents Income
NoneIncome Cap
18Age Support Ends
9%Arrears Interest
🌽 Illinois Income Shares Model
Illinois Child Support Calculator 2026
Illinois uses the Income Shares model — both parents’ net incomes are combined.
ℹIllinois uses net income — Net = gross minus federal taxes, Social Security, Medicare and health insurance premiums.
$
$0$20k
$
$0$20k
$
$
Estimated Monthly Child Support
$0
per month
Annual Total
$0
Combined Income
—
Until Age
18
* Estimate using official Illinois income shares formula. Courts may deviate based on special circumstances. Consult a Illinois family law attorney for your specific situation.
🌽 How Illinois Calculates Child Support
ModelIncome Shares — both parents’ combined net income
Income CapNo set cap — courts use discretion
Minimum Order$40/month minimum regardless of income
Arrears Interest9% annual interest on unpaid arrears
Illinois Key RuleIllinois switched from percentage to Income Shares model in 2017
Additional InfoIllinois courts can order post-secondary educational support — unusual among states
⚖ 50/50 Custody in Illinois
Does Child Support Apply With 50/50 Custody in Illinois?
In most cases, yes. Illinois does not automatically eliminate child support with equal parenting time.
✓General rule: With 50/50 custody, the higher-earning parent typically pays the lower-earning parent. The amount is reduced vs sole custody but rarely reaches $0.
$
$0$15k
$
$0$15k
Estimated Monthly Payment
$0
per month
Without Custody Adj.
$0
Custody Reduction
$0
Net Payment
$0
* 50/50 custody calculations are complex. This is an approximation. Consult a Illinois family law attorney for exact figures.
📋 Illinois Arrears Calculator
Illinois Child Support Arrears Calculator
Calculate total back child support including 9% annual interest Illinois applies to unpaid arrears.
⚠Illinois charges 9% annual interest on all unpaid child support arrears.
$
$
$
Total Arrears Owed (with 9% Interest)
$0
including Illinois 9% annual interest
Base Arrears
$0
Interest Accrued
$0
Clear in 1 Year
$0
Clear in 2 Years
$0
Clear in 3 Years
$0
Support Ends Age
18
* Illinois applies 9% annual interest to unpaid child support. There is generally no statute of limitations on child support debt.
🔄 Modification Estimator
Illinois Child Support Modification
Estimate your new payment and check if you qualify for a modification in Illinois.
ℹModification rule: Most states allow modification when the new amount differs by 15-20% or $100/month, OR when there is a material and substantial change in circumstances (job loss, new child, custody change).
$
36+ months = eligible for routine review
$
Estimated New Monthly Payment
$0
per month
Current Order
$0
New Calculated
$0
Difference
$0
% Change
0%
Likely Qualifies?
—
Time Since Order
—
* Qualification estimate only. Consult a Illinois family law attorney before filing.
📜 Updated 2026
Illinois Child Support Laws 2026
Key rules, age cutoffs and what you need to know in Illinois.
FORMULA How Illinois Calculates Child Support
750 ILCS 5/505 governs child support in Illinois. Illinois is notable for having switched to Income Shares in 2017 AND for allowing courts to order college contribution from parents — called Section 513 support.
AGE When Does Child Support End in Illinois?
Child support in Illinois ends when the child turns 18 — or high school graduation — courts may order college support. Support also ends upon the child’s death, marriage or emancipation. Important: In most cases support does not stop automatically — you need a court order. Stopping payments without a court order creates arrears even after the child reaches the cutoff age.
INTEREST Arrears Interest in Illinois
Illinois charges 9% annual interest on unpaid child support arrears. There is generally no statute of limitations on child support debt.
ENFORCEMENT Illinois Child Support Enforcement
Illinois has broad enforcement powers including wage garnishment, tax refund interception, driver’s license suspension, professional license suspension, passport denial, and credit bureau reporting. Criminal charges may apply for significant or long-term non-payment.
MODIFY Modifying Child Support in Illinois
Child support can be modified in Illinois when there is a material and substantial change in circumstances — typically a significant income change, job loss, new children from another relationship, or change in custody. Most states also allow a periodic review every 3 years. File a petition with the court — private agreements to change support are not legally enforceable.
📅 Illinois Payment Calendar
Child Support Payment Calendar 2026
Generate your personal payment schedule and track payments month by month.
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Monthly Total
$0
Annual Total
$0
Next Payment
—
Days Until Due
—
Payments Remaining
—
Marked Paid
$0
* Click Mark as Paid to track payments. Always keep payment receipts.
Need a Illinois Family Law Attorney?
This calculator provides estimates. For filing, modifying or enforcing a child support order, connect with a local family law attorney.