How Child Support Is Calculated: The 3 State Models Explained (2026)

There is no national child support formula. Instead, all 50 states and D.C. pick one of three models, and which one applies to you can swing the monthly number by hundreds of dollars for identical incomes. Understanding your state’s model is the first step to knowing whether an offer — or a court order — is in the right ballpark.

Model 1: Income Shares (about 40 states)

The most common model. It starts from a simple idea: the child should receive the same proportion of parental income they would have if the parents lived together. The state publishes an economic table (the “schedule of basic obligations”) that maps combined parental income to a basic support amount, and that amount is split between the parents in proportion to their incomes.

Example mechanics: combined monthly income of $8,000 with two children looks up a basic obligation on the state table (say, $1,900). If the paying parent earns 62.5% of the combined income, they owe 62.5% of $1,900 — about $1,188 per month, before adjustments for health insurance and childcare.

Florida, Ohio, Virginia, Pennsylvania, Washington, Colorado, Illinois, North Carolina, Michigan, Georgia, New Jersey, New York, and California all use income shares — though the exact table and the income definition (gross vs. net) differ by state.

Model 2: Percentage of Income (6 states)

Texas, Mississippi, Wisconsin, Nevada, Alaska, and North Dakota apply fixed percentages to the paying parent’s income, largely ignoring the other parent’s income at the basic-calculation stage.

Texas is the clearest example: 20% of net resources for one child, 25% for two, 30% for three, 35% for four, and 40% for five — applied up to a net-resources cap that rose to $11,700 per month on September 1, 2025 (up from $9,200). Wisconsin uses 17/25/29/31/34% of gross income. Nevada uses a tiered percentage that steps down as income rises.

North Dakota is unusual even within this group: its schedule applies to the obligor’s income alone, with no combined-income split at all.

Model 3: Melson Formula (3 states)

Delaware, Hawaii, and Montana use the Melson formula, a more complex variant of income shares. Its distinguishing feature is a self-support reserve: before calculating support, the formula sets aside a subsistence amount for each parent, then applies a “standard of living adjustment” to share additional income with the child. It is the most accurate model in theory and the hardest to reproduce without the state’s official worksheet.

Gross Income vs. Net Income

Even within the same model, states disagree on what income to use. Texas, California, and Illinois calculate on net (after-tax) income; New York, Wisconsin, Georgia, Virginia, and most income-shares states start from gross income. Using the wrong basis is one of the most common self-calculation errors — a net-income state applied to gross figures overstates support substantially.

What the Basic Number Leaves Out

Every model produces a basic obligation. Real court orders then adjust for:

• Health insurance premiums for the child
• Work-related childcare costs
• Parenting time / shared custody (many states reduce support as overnights rise)
• Other children the parent supports
• Extraordinary medical or educational needs

Find Your State’s Number

Our child support calculator implements the official formula for 20 states exactly — including the 2025 Texas cap and the 2026 New York cap — and provides a clearly-labeled estimate plus the official state calculator link for the rest. Select your state to see which model applies and a worked example under your state’s current statute.