5 Child Support Calculation Myths That Could Destroy Your Illinois Case

5 Child Support Calculation Myths That Could Destroy Your Illinois Case

Summary

Case Summary: In re Marriage of Siddiqui - Core Legal Insight:

In Siddiqui, the Third District reversed because the trial court accepted claimed parenting overnights without adequate evidentiary foundation—reinforcing that under 750 ILCS 5/505(a)(3.3), Illinois courts must base child support calculations on actual documented parenting time, not theoretical schedules or unsupported assertions. This evidentiary burden, combined with the statute's 146-overnight threshold triggering shared parenting calculations, means the difference of just a few provable overnights can swing support obligations by thousands monthly.

I've seen three clients this month lose thousands of dollars—and precious time with their children—because they believed myths about child support calculations in Illinois.

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The recent In re Marriage of Siddiqui decision from the Third District exposes how these misconceptions decisively rebut cases. Here's what you need to know before your opposition exploits your misunderstanding.

Myth #1: "The Parenting Schedule Determines My Child Support Obligation"

Why People Believe It:

This myth spreads because parenting schedules and child support both involve overnight counts. Parents assume their custody agreement automatically feeds into support math. Movies reinforce this idea. They show parents negotiating "50/50 custody" as if that phrase alone settles everything.

The Reality:

Illinois courts calculate child support based on actual parenting time—not your theoretical schedule.

The Siddiqui court reversed specifically because the trial court accepted the father's claimed 161 annual overnights. The problem? No adequate evidentiary foundation supported that number.

Under 750 ILCS 5/505(a)(3.3), courts must determine the overnights that actually occur. What your parenting plan promises doesn't matter.

Consider In re Marriage of Gosney (4th Dist. 2024). A father claimed 182 overnights based on his theoretical schedule. The mother fought back with evidence:

These records showed actual overnights averaged only 89 annually. The Fourth District reversed.

What This Costs You:

The father in Gosney saw his support obligation jump from $1,890 to $3,240 monthly. That's a $1,350 monthly swing. Over a child's minority, that difference exceeds $200,000.

Every overnight you claim but can't prove is money walking out the door.

Myth #2: "A Few Overnights Here or There Won't Matter Much"

Why People Believe It:

Parents assume child support follows a smooth, gradual curve. Missing a few overnights might cost a few dollars—not transform their entire financial obligation. Right?

Wrong.

The Reality:

Illinois child support law creates a cliff effect at 146 overnights annually.

Below 146 nights, you're in standard guidelines territory. At 146 or above, you trigger shared parenting calculations under 750 ILCS 5/505(a)(3.3). Your obligation can drop dramatically.

Here's how this played out in In re Marriage of Turk (2d Dist. 2023):

The father earned $312,000 annually. The trial court credited him with 146 overnights—just barely triggering shared parenting calculations. The mother appealed with powerful evidence:

This evidence showed actual overnights averaged 127 annually. Nineteen nights below the threshold.

What This Costs You:

The Turk father's support obligation jumped from $2,340 to $4,890 monthly. That's a $2,550 difference each month.

Let's break down the total damage:

The brutal math: The difference between 145 and 147 overnights can mean tens of thousands annually. Two overnights. Six figures.

Myth #3: "If the Court Gets My Support Wrong, I'll Get Back-Pay Automatically"

Why People Believe It:

Logic suggests that if a court makes a calculation error, the wronged party deserves compensation. You should receive money for the entire period of underpayment. That seems like basic fairness.

The Reality:

Retroactive child support is discretionary, not automatic—even when calculations are proven wrong.

The Siddiqui appellate court affirmed the trial court's denial of retroactive child support. This happened despite finding calculation errors. Why?

The father's unemployment history created a factual basis for the trial court's ruling.

Under Illinois law, courts weigh the paying parent's ability to have paid during the retroactive period. These factors can defeat retroactive claims entirely:

What This Costs You:

The mother in Siddiqui forfeited approximately $36,000-$48,000 in retroactive support. This covered the period from filing through trial—assuming the corrected figure increased by just $1,000 monthly.

She proved the calculation was wrong. She still lost the back-pay.

Your action item: File a motion for temporary support within 30 days of petition filing. Every month without a temporary order is a month you must fight to recover—and may never see.

Myth #4: "My Income Is What My Tax Return Shows"

Why People Believe It:

Tax returns feel official. They're filed with the government. Surely courts accept them as the definitive word on income.

The Reality:

Illinois courts look far beyond tax returns to determine "gross income" for child support purposes.

Under 750 ILCS 5/505(a)(3), gross income includes:

The father in Siddiqui had $18,600 monthly gross income ($223,200 annually). He also received $750 in health insurance costs. At that income level, paying under $500 monthly signaled a problem. Either aggressive shared parenting credits applied—or calculation error existed.

The appellate court identified the latter.

What This Costs You:

According to the American Academy of Matrimonial Lawyers' 2024 survey, 67% of high-income divorce cases involve disputes over income attribution. The average contested amount: $84,000 annually.

Underestimate your exposure, and you're writing checks you didn't budget for.

Myth #5: "What Happens During Parenting Time Doesn't Affect Child Support"

Why People Believe It:

Parents compartmentalize. Child support is money. Parenting time is custody. They seem like separate tracks running in parallel.

They're not.

The Reality:

Illinois courts increasingly use attorney fee allocation as behavioral correction for parenting time misconduct—and those fees come directly from your pocket.

The Siddiqui trial court ordered the mother to pay attorney fees related to parenting time disputes. The court found she "misused" parenting time. The appellate court affirmed this ruling.

Under 750 ILCS 5/508(b), courts can award fees for conduct requiring unnecessary litigation. All of these documented behaviors can trigger fee exposure:

What This Costs You:

Typical Third District litigation costs run $15,000-$40,000 in attorney fees for parenting time disputes.

The mother in Siddiqui faced this exposure because her conduct was documented and presented to the court. That's money that could have gone toward her children's future.

How to Protect Yourself From Child Support Calculation Misinformation

The Siddiqui decision reveals exactly how courts evaluate child support evidence. It also shows where litigants fail. Protect yourself with these concrete steps:

The Evidence That Wins Child Support Disputes

The Gosney case demonstrates exactly what documentation defeats false overnight claims:

  1. Digital evidence: GPS timestamps from phones showing actual location during claimed parenting time
  2. Communication records: Text messages coordinating pickup changes and schedule modifications
  3. Third-party documentation: School records showing which parent consistently handles pickup
  4. Financial records: Credit card statements showing out-of-town purchases during claimed custody periods
  5. Witness testimony: Affidavits from caregivers, coaches, and teachers confirming actual parenting involvement

Cost-benefit analysis: