How Child Support Payments Are Calculated

Child Support Formulas and Calculations

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The federal Child Support Enforcement Act has required all states to implement child support guidelines since 1992, but states have the right to choose which they'll use. All states have adopted one of three different formulas, called models, to determine the appropriate amount of child support payments for each family.

The formulas apply equally to all parents who apply for child support within the state.

The Income Shares Model

The income shares model is based on the assumption that children should receive the same financial support from their parents as they would have enjoyed if their parents had remained together. The incomes of both parents are included in the calculations. Forty-one states used this formula as of 2020.

Calculations begin with how much it costs to raise a child in that particular jurisdiction. Assuming the cost is $1,000 a month per child, the court would then divide this number by the parents' combined incomes. Mom would be responsible for $600 a month if she earns 60% of their combined incomes, while Dad would be responsible for $400 a month if he earns 40%.

Assuming the child lives with Mom, Dad's base child support amount payable to Mom would be $400 per month, or 40% of $1,000. It's assumed that Mom pays her $600 directly via mortgage or rent payments, grocery bills, and the like.

The Melson Formula

The Melson Formula is used in Delaware, Hawaii, and Montana as of 2019. Developed in 1989 by a Delaware Family Court judge, it's a more complex version of the income shares model.

This formula incorporates additional factors and expenses, many of them designed to take parents' financial needs into consideration as well.

The Percentage of Income Model

Another six states use the percentage of income model. As the name suggests, this is either a flat or adjusted percentage of just the non-custodial parent's income.

For example, Texas uses an adjusted or variable version of this model. A noncustodial parent will pay 20% of their monthly "net resources" for one child, graduating up to at least 40% when five children or more require support.


This formula has been criticized as being the most unfair because it doesn't take parenting time or other influencing factors into consideration.

States that use this model include Alaska, Mississippi, Nevada, North Dakota, Texas, and Wisconsin as of 2020.

Parental Income

Income can be net or gross. Take-home pay is considered to be net income.

It can include lottery winnings, stock valuations, and future income. It might also include the monetary value of benefits such as the use of a company car or a military housing allowance.

Parents are required to provide courts with copies of their most recent W-2 forms, pay stubs, and documentation supporting any other types of income they might have. Self-employed parents' incomes are typically based on their tax returns.

Other Dependents

Most states will factor in support paid for other child dependents not included in the child support order that's being calculated. For example, a parent might already be paying child support for a child of another relationship, or be supporting one or more children who currently live with them.

Parenting Time Factors

The income shares model is set up to accommodate the amount of time a child spends with each parent, which is generally based on the number of overnights the child spends in each home per month.

The custodial parent receives credit for paying for the child's needs directly during time spent in that home. Likewise, the parent with parenting time is credited with paying the child's expenses directly during visitation time spent in that parent's home.

Special Considerations

States can impose a higher level of support for higher-than-average medical or educational expenses, or for special needs children who might incur additional expenses, such as speech therapy.


Some state courts might also consider the costs of recreational activities, such as sports camps or after-school activities.

Most states that use the income shares model apply the same mathematical formula for work-related child care costs and health insurance premiums, dividing them between parents based on their percentage contributions to their combined incomes.

How the Cost of College Impacts Child Support

A child support obligation ends when a child reaches the age of maturity, which is usually age 18, but is age 21 in some states. The obligation to support a child in college depends on the state that orders the support.

To learn more about child support payments and obligations in your jurisdiction, please visit your state's family court website.

Child Support by Agreement

Most states permit parents to reach their own agreements as to how much child support will change hands. Judges might consent to a different arrangement if extenuating circumstances make the state's child support guidelines unreasonable and the parents can agree on how much should be paid. Parents receiving any form of public support don't have this option, however.

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The Balance uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Department of Justice. "Child Support Enforcement."

  2. National Conference of State Legislatures. "Child Support Guideline Models."

  3. Texas Constitution and Statutes. "Family Code: Title 5. the Parent-Child Relationship and the Suit Affecting the Parent-Child Relationship."

  4. National Conference of State Legislatures. "Child Supporting and Parenting Time Orders."

  5. National Conference of State Legislatures. "Termination of Child Support."

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