How to Calculate Child Support Payment Obligations: The State-by-State Math

Two Models Govern Nearly Every U.S. Child Support Calculation

Your state uses one of two formulas. Most states use the Income Shares model. A smaller group, including Texas and Wisconsin, uses the Percentage of Income model. The distinction matters immediately because each model starts from a different data point.

Income Shares model: Both parents' incomes combine into a single figure. The state's support schedule assigns a dollar amount to that combined income. Each parent's share of that amount is proportional to their individual income contribution.

Percentage of Income model: Only the paying parent's income enters the formula. The state applies a fixed percentage based on the number of children. The receiving parent's income is largely irrelevant.

Same parental earnings, different model, different obligation. A non-custodial parent earning $72,000 per year with one child owes roughly $1,008 per month in Texas under the Percentage of Income model (14% of net resources). In Illinois, which uses Income Shares, the same parent's obligation against a custodial parent earning $48,000 per year works out to approximately $790 per month. The gap is $218 per month, or $2,616 per year.

How the Income Shares Calculation Works: A Worked Example

The Income Shares calculation follows four steps.

Step 1: Establish gross income for both parents. Parent A (non-custodial) earns $6,000 per month gross. Parent B (custodial) earns $4,000 per month gross. Combined monthly income is $10,000.

Step 2: Apply the state's basic support obligation schedule. Most states publish an official child support schedule table. For a combined monthly income of $10,000 with one child, a typical Income Shares state assigns a basic support obligation of approximately $1,450 per month.

Step 3: Calculate each parent's proportional share. Parent A contributes 60% of combined income ($6,000 / $10,000). Parent B contributes 40%. Parent A's share of the basic obligation is 60% of $1,450, which equals $870 per month.

Step 4: Add extraordinary expenses. Work-related childcare costs and unreimbursed medical expenses allocate between parents in the same 60/40 ratio. If monthly childcare runs $600, Parent A owes an additional $360. Total obligation: $870 + $360 = $1,230 per month.

How the Percentage of Income Calculation Works: A Worked Example

Texas calculates child support based exclusively on the paying parent's net resources, defined in Texas Family Code Section 154.062.

Step 1: Calculate net resources. Non-custodial parent earns $85,000 per year gross. Federal income tax at the single-filer rate for this income level reduces take-home pay. Social Security tax (6.2%) and Medicare tax (1.45%) apply. Texas has no state income tax. Net monthly resources after these deductions approximate $5,620.

Step 2: Apply the statutory percentage. Texas specifies 14% of net resources for one child. Two children: 20%. Three children: 25%. Four children: 30%. Five or more children: 40%.

For one child: 14% of $5,620 = $786.80 per month. For two children: 20% of $5,620 = $1,124 per month.

Note: Texas caps the percentage calculation at $9,200 in net monthly resources as of the current statutory cap. Income above that cap requires a separate best-interest-of-the-child analysis for additional support.

Parenting Time Adjustments Reduce the Obligation Significantly

Shared physical custody reduces the paying parent's obligation in most states. The mechanism varies, but the financial effect is substantial.

Under Colorado's parenting-time adjustment schedule, once a non-custodial parent has 93 or more overnights per year (roughly 25.5% of the year), the court applies an offset calculation. At 146 overnights (40% of the year), the adjustment can reduce a base obligation of $1,100 per month down to approximately $660 per month, a 40% reduction.

Parents who negotiate additional parenting time without quantifying this credit leave money on the table. Every additional overnight above the threshold has a calculable dollar value. At a base obligation of $1,100, moving from 100 overnights to 146 overnights per year saves approximately $5,280 annually in Colorado.

Document every overnight. Courts require evidence, not estimates.

Income Definitions Include More Than a W-2 Salary

Courts define income broadly. Failing to account for all income sources, on either side, produces an inaccurate baseline and risks contempt or modification proceedings later.

Sources that states routinely include in gross income calculations:

• W-2 wages and salary
• Self-employment income, net of ordinary and necessary business expenses (but not depreciation in many states)
• Rental income
• Dividend and interest income
• Social Security Disability Insurance payments
• Workers' compensation benefits
• Unemployment insurance payments
• Stock option income in the year of exercise

Self-employed parents face additional scrutiny. Courts often add back depreciation and certain business deductions when calculating income available for support. A business owner reporting $40,000 in net Schedule C income after $22,000 in depreciation may have $62,000 attributed as income for support purposes.

Allowable Deductions That Reduce the Base Obligation

Both the Income Shares and Percentage of Income models allow specific deductions before applying the formula.

Common deductions include:

• Pre-existing child support orders for other children
• Health insurance premiums paid for the child
• Work-related childcare expenses
• Extraordinary medical expenses above a threshold (typically 5% of gross income)

A parent paying $280 per month in health insurance premiums specifically for the child, plus $450 per month in documented work-related childcare, reduces a $1,230 gross obligation by a combined credit of $440 to $510 depending on the state's allocation method. The net obligation drops to approximately $720 to $790 per month.

Keep receipts, invoices, and insurance statements. These deductions require documentation at every modification hearing.

Run Your Numbers Before the Hearing

Arriving at a child support negotiation without your own calculated figure is a costly mistake. Attorneys and mediators run these numbers in advance. You should too.

The CalcMoney child support calculator applies the Income Shares and Percentage of Income model mechanics to your specific income figures, parenting schedule, and allowable deductions. It produces a documented monthly estimate you can bring to mediation or use to audit a proposed court order.

Enter both parents' gross monthly incomes, the number of qualifying children, your state, and your documented childcare and healthcare costs. The calculator returns your base obligation, your proportional share, and the parenting-time-adjusted figure where applicable.

Courts set child support orders using the same formula inputs. Running your own calculation in advance means no numbers presented in that room will surprise you.

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Results are estimates for informational purposes only. Consult a licensed financial professional before making financial decisions.