The formula depends on your state, both parents' income, and custody time

Child support is calculated using a formula set by your state, not by a judge's discretion. The formula takes your income, the other parent's income, how much time each parent spends with the child, and sometimes childcare costs or health insurance premiums. Most states use one of three models: the income shares model (used by most states), the percentage of income model (used by a few states), or the combined income model (used by fewer states). The result is a monthly amount one parent pays to the other.

The calculation starts with gross income, which includes wages, self-employment income, bonuses, rental income, and sometimes unemployment or disability benefits. It does not include child support you already pay for other children or spousal support you already pay. Each state defines what counts as income differently, so the same earnings can produce different support amounts in different states.

Once income is established, the state applies its formula. In income shares states, both parents' incomes are combined, and the formula calculates what percentage of that combined income should go to the child. That percentage is then split between the parents based on how much each earns. In percentage of income states, the formula is simpler: a set percentage of the paying parent's income, often adjusted for how many overnights the child spends with each parent.

Key Takeaways

  • Every state has a written formula for calculating child support, and the amount is based on both parents' income and the time each parent spends with the child.
  • Gross income includes wages, self-employment earnings, bonuses, and some benefits, but the definition of what counts varies by state.
  • The three main calculation models are income shares (most common), percentage of income, and combined income, and your state uses one of these.
  • Custody time affects the calculation because more overnights with the paying parent usually lowers the support amount.
  • The calculated amount is a guideline, and a judge can order a different amount if the guideline would be unjust or inappropriate in your situation.

How your state's income shares model works

In income shares states, the first step is combining both parents' gross income. The state then has a table or formula that shows what percentage of that combined income should support the child or children. For example, one state's table might say that 20 percent of combined income supports one child, 32 percent supports two children, and 40 percent supports three children. These percentages are set by state law and change only when the legislature updates them.

Once the total support obligation is calculated, it is divided between the parents based on their income ratio. If one parent earns 60 percent of the combined income and the other earns 40 percent, the first parent pays 60 percent of the total obligation. The parent with primary custody (more overnights) usually pays a smaller share because the other parent is already spending money on the child during their time.

The income shares model also accounts for childcare costs needed so one parent can work, health insurance premiums paid for the child, and sometimes extraordinary medical expenses. These are added to the base obligation and split the same way as the base amount.

How custody time changes the calculation

The number of overnights each parent has with the child directly affects the support amount. A parent who has the child 50 percent of the time pays less support than a parent who has the child 10 percent of the time, because the first parent is already spending money on food, utilities, and housing while the child is present.

States define custody time differently. Some count overnights; others count days. Some have thresholds—for example, if one parent has fewer than 110 overnights per year, the formula applies one way, but if they have 110 or more, it applies differently. A few states ignore custody time entirely and base support only on income, though this is less common.

If custody changes after the support order is entered, the support amount can change. A parent who gains more overnights may owe less support; a parent who loses overnights may owe more. The change usually requires a new court order, not an automatic adjustment.

What happens when income is hard to calculate

Self-employed parents, parents with irregular income, and parents who own businesses present a calculation problem because their income varies. The court may average income over a period of time, use tax returns from multiple years, or add back business expenses that the parent deducted on taxes but did not actually reduce their ability to pay support.

A parent who is unemployed or underemployed may be assigned imputed income—an income amount the court decides they could earn if they worked. The court considers the parent's age, education, work history, and local job market. A parent cannot straightforward quit work to lower their support obligation; the court will impute income based on what they could earn, not what they choose to earn.

Parents who receive bonuses, commissions, or seasonal income must usually report these to the court. The court may average them over time or treat them separately from base salary. Some states require that bonuses and commissions be included in the calculation; others leave this to the judge's discretion.

Deviations from the guideline amount

The calculated amount is a guideline, not an automatic order. A judge can order a different amount if explore the guideline would be unjust or inappropriate. Common reasons for deviation include one parent having substantial assets or income beyond what the formula captures, one parent having very high income that would produce an unreasonably large support amount, or one parent having significant debt obligations.

A judge can also deviate if the child has special needs, if one parent is paying support for other children, or if the parents agree to a different amount in writing. Some states require the judge to state in writing why they deviated from the guideline; others do not.

Deviations are not common, and a judge will not deviate straightforward because a parent asks. The parent requesting a deviation must show that explore the guideline would be unjust, and the burden is on them to prove it.

How to find your state's specific formula

Your state's child support formula is published in state law, usually in the family law or domestic relations section of the state code. You can find it through your state legislature's website or through your state court system's website. Many states also publish worksheets that show how to calculate support step by step.

Your state's child support enforcement agency (usually part of the Department of Human Services or Department of Social Services) often has a calculator on its website that shows roughly what support would be under your state's formula. These calculators are informational only and do not produce a court order, but they can give you a starting point.

If you are working with a lawyer, they will have access to the formula and can calculate the likely amount based on your specific income and custody situation. If you are representing yourself, reading your state's statute and using your state's worksheet is the most accurate way to understand how the calculation works.

Frequently Asked Questions

Does child support change automatically if my income changes?

No. Support is based on the income reported at the time of the order. If your income changes significantly, either parent can ask the court to modify the order, but the court will not automatically recalculate. Most states allow modification if income has changed by a certain percentage (often 10 to 15 percent) or by a certain dollar amount.

Can I deduct taxes or other expenses from my income before the formula is applied?

No. The formula uses gross income, not net income after taxes. However, some states allow deductions for certain things like existing child support obligations for other children, spousal support you already pay, or mandatory retirement contributions. Your state's statute will specify what can be deducted.

What if one parent makes much more money than the other?

The formula still applies, but some states have an income cap. For example, a state might say the formula applies to combined income up to $150,000 per year, and anything above that is left to the judge's discretion. This prevents the formula from producing unreasonably high support amounts when one parent has very high income.

Does the child's age matter in the calculation?

Most states use the same formula regardless of the child's age. A few states adjust the amount as the child gets older, on the theory that older children cost more. Your state's statute will say whether age is a factor.

Can parents agree to a different amount than what the formula produces?

Yes, but the agreement must be in writing and approved by a judge. The judge will review the agreement to make sure it is not unfair to the child. If both parents agree and the judge approves, the agreed amount becomes the court order, even if it differs from the guideline.