Income Shares vs. Percentage of Income: Child Support Models Explained

The Two Main Child Support Models in the United States

Here's the short answer: federal law — 42 U.S.C. § 667 — forces every state to adopt guidelines, and states picked one of three models. Roughly 41 use income shares (both parents' incomes matter).

A handful — Texas, Wisconsin, Mississippi, North Dakota — use straight percentages off the noncustodial parent's income only. Delaware, Hawaii, and Montana use the more complex Melson formula. The model your state picked changes your number more than any other variable.

The income shares model, used by approximately 41 states, considers both parents' incomes and attempts to replicate the percentage of combined income that would have been spent on the child if the family were intact. The percentage of income model, used by states including Texas, considers only the noncustodial parent's income. For more on how states calculate support, see our state-by-state child support guide.

The model your state uses can significantly affect the support amount, especially when there is a large income disparity. Run your numbers through our Child Support Estimator to see how your state's formula works.

How the Income Shares Model Works

The income shares model begins by combining both parents' gross or net incomes. The combined income is compared to a state-published table showing the estimated cost of raising a child at each income level. These tables are based on economic research (originally the Betson-Rothbarth model) estimating what intact families spend on children.

The total child support obligation from the table is divided between parents in proportion to their individual incomes. If Parent A earns 60% of the combined income and Parent B earns 40%, Parent A is responsible for 60% of the obligation.

The custodial parent's share is presumed spent directly on the child through housing, food, and daily expenses. The noncustodial parent pays their share as a monthly payment.

Most income shares states also adjust for health insurance, childcare costs, and extraordinary expenses. Some states apply a parenting time credit reducing the noncustodial parent's obligation when they have substantial custodial time—typically more than 25% to 30%. See our article on custody time and child support for details.

How the Percentage of Income Model Works

The percentage of income model bases the child support obligation on the noncustodial parent's income alone, regardless of the custodial parent's income. This makes the calculation straightforward but ignores the economic reality that both parents contribute to raising a child.

Texas provides the clearest example. Under Texas Family Code §154.125, the noncustodial parent pays 20% of net resources for one child, 25% for two, 30% for three, 35% for four, and 40% for five.

The percentage applies to the first $11,700 per month of net resources (2026 cap). Use our Texas Child Support Estimator to calculate a specific amount.

The main criticism is that it can produce inequitable results when the custodial parent has substantially higher income. Wisconsin, Mississippi, and North Dakota also use variations of this model, though some have incorporated income shares elements.

Side-by-Side Comparison With Real Numbers

Consider a family with one child where Parent A (noncustodial) earns $5,000/month net and Parent B (custodial) earns $3,000/month net. In Texas, Parent A would pay 20% of $5,000, or $1,000/month. Parent B's income is irrelevant.

In a typical income shares state, the combined income is $8,000. The schedule might set the obligation at $1,200/month.

Parent A earns 62.5%, so their share is $750/month. The income shares result ($750) is 25% lower than the percentage result ($1,000) in this scenario.

Now reverse the incomes: Parent A earns $3,000, Parent B earns $5,000. In Texas, Parent A pays $600/month.

In an income shares state, combined income is still $8,000 and the obligation is $1,200, but Parent A now owes 37.5%, or $450. The income shares model produces a lower obligation when the noncustodial parent is the lower earner. Try our Child Support Estimator with your actual numbers.

The Melson Formula: A Third Approach

The Melson formula, used by Delaware, Hawaii, and Montana, adds a self-support reserve for each parent and a standard of living adjustment (SOLA). The self-support reserve ensures neither parent is impoverished by the support obligation—it sets aside a basic living allowance based on the federal poverty level before calculating support.

After the self-support reserve is deducted, the Melson formula calculates a basic obligation similar to income shares. Then, if the paying parent's income exceeds combined basic needs, a SOLA percentage of 10% to 15% is applied to excess income and added to support.

The Melson formula tends to produce lower support for low-income parents (self-support reserve) and higher amounts for high-income parents (SOLA). It is considered the most equitable model by family law academics, but its complexity has prevented widespread adoption. For specific formulas, see our state-by-state guide.

Which Model Does Your State Use?

The vast majority of states use income shares, including California, Florida, New York, Ohio, Pennsylvania, Illinois, Georgia, Virginia, Michigan, and many others. Each has its own income schedule and specific rules about what counts as income.

States using percentage of income include Texas, Wisconsin, Mississippi, and North Dakota, though some have incorporated income shares elements. The Melson formula is used only in Delaware, Hawaii, and Montana. The national trend is firmly toward income shares.

Our Child Support Estimator applies the correct formula for your jurisdiction. Select your state: California, Texas, Ohio, and all others are available. For how support interacts with custody, see our articles on custody time and child support and the child custody guide.