How Is Child Support Calculated?

When parents live apart, child support is the court-ordered amount one parent pays the other to help cover a child’s everyday costs. Every U.S. state has its own guidelines and its own math, but nearly all of them build on one of the same three formulas. Here’s how those formulas work, what counts as income, and where to check the exact numbers for your state.

The Three Calculation Models

States choose one of three basic approaches to set a guideline amount:

  • Income Shares Model — used by the large majority of states. Both parents’ incomes are added together, a table estimates what that combined household would spend on the children, and the total is split between the parents in proportion to what each one earns.
  • Percentage of Income Model — used by a smaller group of states, including Texas. Only the paying parent’s (the “obligor’s”) income is used; a set percentage is applied based on the number of children, either as a flat rate or one that changes with income level.
  • Melson Formula — used by Delaware, Hawaii, and Montana. A more detailed version of the income-shares approach that first sets aside a minimum self-support amount for each parent before dividing what’s left.

What Counts as Income

Most guidelines start from a broad definition of income, including:

  • Wages, salary, overtime, commissions, and bonuses
  • Self-employment or business income
  • Rental, investment, retirement, and Social Security income
  • Unemployment and disability benefits

Courts can also “impute” income — estimate what a parent could reasonably earn — if that parent is voluntarily unemployed or underemployed.

Common Adjustments to the Base Number

  • Health insurance premiums covering the child
  • Work-related childcare costs
  • Extraordinary medical, educational, or special-needs expenses
  • How many overnights each parent has with the child

Why Every State Has to Do This

Federal regulation (45 CFR Part 302.56) requires every state to publish numeric child support guidelines and review them at least once every four years. Whatever the guideline formula produces is presumed correct — a judge can deviate from it, but generally has to explain in writing why the standard number wouldn’t be fair in that case.

Estimating Your Own Number

Because the model, the percentages, and the income caps are all set at the state level, the fastest way to get a realistic figure is to run your numbers through a calculator built around your state’s formula. The Child Support Calculator walks through this by state and gives you a starting estimate before you talk to a court, mediator, or attorney.

Official Resources

This guide is for general information only and is not legal advice. Formulas, percentages, and dollar caps change over time and courts can deviate from the guideline result — confirm current figures with the official resources above or a family law attorney before relying on any number.