What Child Support Actually Costs and How It's Calculated

Child support amounts vary by state and depend on each parent's income

There is no single national child support amount. Every state has its own formula, and the payment changes based on how much each parent earns, how much time each parent spends with the child, and sometimes the cost of childcare or health insurance. A parent in one state might pay $300 a month for one child while a parent in another state with the same income pays $450.

Most states use one of three calculation methods: the income shares model (used by about 40 states), the percentage of income model (used by a few states), or the Melson formula (used by Delaware, Hawaii, and Maryland). Each method starts with the parents' gross income and then applies different percentages or formulas to reach a final number.

The payment amount is not permanent. If either parent's income changes significantly, or if custody arrangements change, the amount can be modified through the court that issued the original order.

Key Takeaways

• Child support is calculated using your state's specific formula, which typically starts with both parents' gross income and adjusts for custody time and certain expenses.
• The amount varies widely by state — the same income level can result in different monthly payments depending on where you live.
• Most states use the income shares model, which divides the cost of raising a child between parents based on their income percentages.
• You can request a modification if either parent's income drops by a certain percentage (usually 10 to 15 percent) or if custody time changes significantly.

How the income shares model works

The income shares model is the most common approach. It starts by adding both parents' gross monthly income together, then subtracts certain costs like health insurance premiums, existing child support obligations, and sometimes childcare expenses. The result is called the "combined parental income."

Each state publishes a child support guideline table that shows what percentage of combined income should go toward child support based on the number of children. For example, a state's table might say that 20 percent of combined income goes to one child, 32 percent to two children, and 40 percent to three children. The court applies this percentage to the combined income to get a base amount.

That base amount is then divided between the parents based on what percentage of the combined income each parent earns. If one parent earns 60 percent of the combined income and the other earns 40 percent, the first parent pays 60 percent of the base amount. The parent with primary custody may also receive a credit for direct expenses like housing and food.

How the percentage of income model works

A smaller number of states use the percentage of income model, which is simpler: the non-custodial parent (the one who does not have primary custody) pays a set percentage of their gross income for child support. The percentage varies by state and by the number of children — it might be 17 percent for one child, 25 percent for two, 29 percent for three, and so on.

This model does not account for the custodial parent's income in the same way the income shares model does. It focuses on the non-custodial parent's ability to pay. Some states that use this model do make adjustments if the custodial parent's income is very high or if there are significant childcare costs.

What counts as income for child support

Gross income is the starting point for almost every calculation. This includes wages from employment, salary, bonuses, commissions, and tips. It also includes income from self-employment, rental property, investments, pensions, and Social Security benefits (though Social Security for the child themselves is usually excluded).

Some types of income are excluded or treated differently depending on the state. Means-tested benefits like Supplemental Security Income (SSI) or Temporary information for Needy Families (TANF) are often not counted. Unemployment benefits, workers' compensation, and disability payments may or may not be included depending on your state's rules.

If a parent is intentionally underemployed — earning less than they could — the court may "impute" income, meaning it assigns an income level based on what the parent could reasonably earn. This prevents someone from lowering their child support by taking a lower-paying job on purpose.

Adjustments that affect the final amount

The base calculation is rarely the final number. States allow deductions and credits that lower the amount owed. Health insurance premiums for the child are almost always deducted. Childcare costs required for work or school are deducted in most states. Some states deduct the cost of work-related transportation.

Custody time also affects the amount. If both parents share custody roughly equally, the calculation changes because both parents are providing direct care and housing. The parent with less income may owe less or nothing, depending on the exact split and the income difference.

If a parent is already paying child support for other children from a previous relationship, that obligation is usually deducted from their income before the new calculation is made. This prevents one parent from being unable to support multiple sets of children.

How to find your state's specific formula

Your state's child support guidelines are public documents, usually available through your state's Department of Human Services, Department of Social Services, or the court system's website. Searching "[your state] child support guidelines" will typically lead you to the official guideline table and the formula your state uses.

Many state websites include a child support calculator tool where you can enter both parents' income and custody arrangement to see an estimate. These calculators use the official state formula and can give you a rough idea of what the amount might be, though the actual court order may differ based on other factors.

If you are going through the court system, the judge or child support officer will use these same guidelines. The order must state the reason if the final amount differs from what the guidelines suggest — this is called a "deviation" from guidelines.

What happens if income changes

Child support orders remain in effect until the child reaches the age of majority (usually 18, sometimes 19 or 21 depending on the state) or until the order is modified. If a parent's income changes significantly, either parent can ask the court to modify the amount.

Most states allow a modification request if income has changed by a certain percentage — often 10 to 15 percent — or if there has been a substantial change in circumstances like a job loss, a major increase in income, or a change in custody time. The parent requesting the modification must file a motion with the court and provide proof of the income change, such as recent pay stubs or tax returns.

The modification process varies by state. Some states allow it to be done through the child support enforcement agency, while others require going back to court. The new amount typically takes effect from the date the motion is filed, not retroactively to when the income changed.

Frequently Asked Questions

Does child support end when the child turns 18?

In most states, yes — child support ends when the child reaches the age of majority, which is 18 in most places. However, some states extend it to 19 or 21 if the child is still in high school or has not yet graduated. A few states may extend support if the child has a disability. The original court order should state the end date.

What if the paying parent loses their job?

A job loss is a substantial change in circumstances that can justify a modification request. However, the parent must file a motion with the court — the obligation does not automatically pause. If payments are missed while waiting for a court hearing, the arrears (back payments) still accumulate. It is important to file the modification request as soon as possible after a job loss.

Can child support be modified if the custodial parent's income increases?

Yes. If the custodial parent's income increases significantly, the non-custodial parent can request a modification to lower the amount. The calculation depends on your state's formula, but in most cases a substantial income increase for either parent is grounds for modification.

Is child support the same as alimony or spousal support?

No. Child support is for the benefit of the child and is based on the child's needs and both parents' incomes. Alimony (also called spousal support or maintenance) is paid by one ex-spouse to the other and is based on different factors like the length of the marriage and the earning capacity of each spouse. They are separate obligations.

What if both parents have equal income and equal custody time?

When income and custody time are equal, the base child support amount may be zero or very low, depending on your state's formula. However, one parent may still owe the other to cover specific expenses like health insurance or childcare that are not split equally. The court order will specify what, if anything, is owed.