Child support in the US: how it is calculated, changed and enforced

Money worries hit hardest when children are involved. If you are about to pay support, you may be wondering whether you can still afford a place where your kids can stay with you. If you are about to receive it, you may be wondering whether it will cover anything at all, or arrive on time. Both fears are reasonable, and both get smaller once you see how the system actually works.

The short version: federal law requires every state to have one set of child support guidelines, to review them at least every four years, and to treat the guideline amount as presumptively correct. A judge can depart from it only with written findings that the guideline result would be unjust or inappropriate. So the formula is not a starting offer. It is usually the answer.

The three guideline models

According to the National Conference of State Legislatures, states use one of three models.

Income shares (most states)

Forty-one states, plus Guam and the U.S. Virgin Islands, use income shares. The idea is that a child should get the same share of parental income they would have received if the family had stayed together. The steps are roughly:

1. Add both parents' incomes together, using the state's definition of income.
2. Look up the basic support amount for that combined income and number of children on the state's schedule.
3. Split that amount between the parents in proportion to their incomes.
4. The parent with less parenting time pays their share to the other parent. The other parent's share is assumed to be spent directly on the children.

Illustrative example only (not any state's real numbers): Parent A earns $6,000 a month and Parent B earns $4,000, so A has 60% of the combined $10,000. If a state schedule showed $1,800 a month for two children at that income, A's share would be $1,080 and B's $720. If the children live mainly with B, A would pay B about $1,080 a month, before add-ons and any adjustment for A's parenting time. Your state's schedule and income rules will produce a different figure.

Percentage of income

Six states (Alaska, Mississippi, Nevada, North Dakota, Texas and Wisconsin) use a percentage of income model. Support is a set percentage of the paying parent's income, which rises with the number of children. The receiving parent's income generally does not change the basic number, though it can matter for add-ons and deviations.

Melson formula

Three states (Delaware, Hawaii and Montana) use the Melson formula. It is a more detailed version of income shares that first sets aside a basic self-support amount for each parent, then covers the child's primary needs, then shares any remaining income with the child through a standard-of-living adjustment.

Every state publishes its own worksheets and, usually, an online calculator. Use your state's official one. FairWell's free calculators can give you a first estimate, and your state page links to local rules.

What counts as income

The definition of income is where most arguments happen, because it moves the number more than anything else. Federal rules require guidelines to be based on the paying parent's earnings, income and other evidence of ability to pay. State definitions are broad and usually include:

• wages, salary, overtime, commissions and bonuses;
• self-employment and business income, often after reasonable business expenses only;
• rental, investment and interest income;
• unemployment and workers' compensation benefits, pensions and some disability benefits;
• sometimes regular gifts or perks such as a company car or free housing.

Some states start from gross income and others from net income, so two states can produce very different results for the same family.

Imputed income. If a parent is voluntarily unemployed or underemployed, courts can assign them the income they could reasonably earn. Federal rules say states must take a parent's actual circumstances into account when imputing income, and incarceration cannot be treated as voluntary unemployment. If your income is irregular or comes from your own business, read how support works for self-employed and variable income.

Shared parenting time and add-ons

Shared parenting adjustments. Many states reduce support when the paying parent has the children for a significant share of overnights, on the logic that they are spending money on the children directly during that time. The threshold and the formula vary a great deal from state to state. Count overnights carefully using your state's method before you agree to a schedule, and never trade parenting time for money. Courts look at the two separately, and children notice.

Health insurance. Federal rules require state guidelines to address how parents will cover the child's health care needs, through private or public coverage. In practice, the cost of the child's portion of insurance premiums is usually added to the support calculation and shared, and orders often say how uninsured medical, dental and vision costs will be split. If the insurance is through one parent's employer, plan now for what happens if that job changes. Our guide to health insurance after separation covers the options.

Childcare. Most states add work-related or education-related childcare costs to the calculation and split them between the parents, often in proportion to income.

Other expenses. Some states allow additions or deviations for extraordinary expenses such as private school, special needs or costly activities. Write down exactly how these are shared, who must agree before spending, and how quickly the other parent reimburses. Vague clauses create years of small fights.

Taxes. Child support is not deductible by the parent who pays it and is not taxable income for the parent who receives it. Tax benefits such as claiming the child as a dependent follow separate IRS rules; see our guide to US tax after divorce.

How long support lasts

Support usually continues until the child reaches the age of majority in that state, commonly 18 or the end of high school. Some states go further. In New York, for example, parents must support a child until 21 unless the child becomes emancipated earlier. Some states allow support to continue for an adult child with a disability. Check your state's rule before you sign, so the end date in your agreement is correct.

Changing the amount

Child support is never fixed forever. Either parent can ask for a modification when there has been a substantial change in circumstances, such as a significant change in income, a change in where the children live, or new costs like health needs or childcare.

If your case is handled by the state child support agency, federal rules require the agency to review the order at least every 36 months when a parent asks, and to review sooner if a parent shows a substantial change. The agency must also notify both parents when the paying parent will be incarcerated for more than 180 days, so they can ask for a review.

The most important practical point: file as soon as your circumstances change. Federal law generally prevents courts from reducing support that is already past due, so a change usually only counts from the date you ask for it. An informal agreement with your ex to pay less does not change a court order, and the full amount can still be collected later.

Enforcement and the Title IV-D agencies

Every state runs a child support program under Title IV-D of the Social Security Act. Any parent can apply, whether or not they receive public assistance, and the services are free or low-cost. Families who have never received assistance may be charged an annual federal user fee of $35 once at least $550 has been collected in a year. Agencies can:

• locate a parent and establish paternity;
• set up and modify support orders;
• collect and distribute payments, usually through automatic income withholding from wages;
• enforce medical support.

When payments stop, enforcement tools include wage withholding through new-hire reporting, interception of federal and state tax refunds, bank account levies, liens on property, credit bureau reporting, driver's and professional license suspension, and passport denial once arrears reach $2,500. Courts can also find a parent in contempt. Every state has adopted the Uniform Interstate Family Support Act, which governs cases where the parents live in different states.

Even if you get along well now, routing payments through the state's disbursement unit creates a clean record of what was paid and when. If you are already owed money, our guide to enforcing support when your ex won't pay walks through the next steps.

What to do this week

1. Find your state's official guideline worksheet and calculator. Your state court or child support agency website will have them. Note whether your state uses gross or net income.
2. Gather income proof for both parents. Recent pay stubs, the last two or three tax returns and any business records. If you don't have your co-parent's, list what you know.
3. Price the add-ons. Get the actual cost of the children's health insurance premiums and childcare so they go into the calculation as real numbers.
4. Count overnights honestly. Use a calendar for a full year, including holidays, and check your state's shared parenting rule.
5. Decide how payments will flow. Consider opening a case with your state's IV-D agency or using income withholding from day one.
6. Have the numbers checked. A family law attorney or mediator in your state can confirm the calculation before anything is signed.

Common questions

Can parents agree to a different amount of child support than the guidelines?

Often yes, but a court usually has to approve it. Because the guideline amount is presumed correct, a judge will typically want to know why a different amount is in the child's interests, and federal rules require written findings for any deviation from the guidelines. Parents generally cannot waive a child's right to support.

Is child support taxable?

No. Child support is not deductible by the parent who pays it and is not taxable income for the parent who receives it.

Does having 50/50 custody mean no child support?

Not necessarily. Many states adjust support for shared parenting time, but if one parent earns more, that parent may still pay support to the other. The result depends on your state's formula and both incomes.

Can I stop paying child support if I lose my job?

No. The order stays in force until a court or agency changes it. Ask for a modification as soon as your income drops, because past-due support generally cannot be reduced after the fact.

Do I have to be on public assistance to use the state child support agency?

No. Title IV-D child support services are available to any parent. Families who have never received public assistance may pay a small annual federal fee once a set amount has been collected.

Official sources

• 45 CFR 302.56: requirements for child support guidelines (Cornell Legal Information Institute)
• 45 CFR 303.8: review and adjustment of child support orders (Cornell Legal Information Institute)
• Child support guideline models (National Conference of State Legislatures)
• Office of Child Support Services, information for parents (U.S. Administration for Children and Families)
• Publication 504, Divorced or Separated Individuals (IRS)

This guide is legal information, not legal advice, and it is written for a general audience across Canada and the United States. Family law is provincial and state-based and changes over time. Before you rely on anything here for your own situation, confirm it with a qualified family lawyer in your province or state. FairWell can connect you with one through the professional directory.