Quick answer: States set child support with a guideline formula built on one of three models: income shares, a percentage of the paying parent's income, or the Melson formula. Federal law requires every state to have guidelines, and the result is presumed correct unless a court finds it unjust or inappropriate. Income, child care, health coverage and parenting time all feed the number.
On this page:
- Why every state has a child support guideline
- The three guideline models
- How the income shares model works
- What income counts
- Child care, health care and other add-ons
- How parenting time changes the number
- When a court can depart from the guideline
- How to find your number
Why every state has a child support guideline
Child support is the sum the noncustodial parent pays toward the child’s basic living expenses, such as food, clothing, shelter, health care and education. Federal law makes states use a formula to set it: 42 U.S.C. 667 requires guidelines, review at least every four years, and a rebuttable presumption that the amount the guideline produces is the correct amount. The federal rule at 45 CFR 302.56 sets the minimum content, and each state then chooses the model and the numbers. That is why the answer to “how is child support calculated?” starts with your state.
The three guideline models
According to the National Conference of State Legislatures, states generally use one of three models to set the base amount.
| Model | How it works | Who uses it |
|---|---|---|
| Income shares | Both parents’ incomes are combined and the child gets the share of income he or she would have had if the parents lived together | The remaining 41 states |
| Percentage of income | A percentage of the paying parent’s income only; the other parent’s income is not counted | Alaska, Mississippi, Nevada, North Dakota, Texas, Wisconsin |
| Melson formula | A more complex income shares model that first covers each parent’s basic needs and then the children’s | Delaware, Hawaii, Montana |
| Hybrid | Starts as a varying percentage of income, then is reduced by a formula based on the custodial parent’s income | District of Columbia |
Within the percentage model, Alaska, Mississippi, Nevada and Wisconsin use a flat percentage, while North Dakota and Texas use a varying percentage. Which model applies to you changes everything downstream, so start with the Child Support Calculator for your state.
How the income shares model works
Most states estimate what it costs to raise a child at the parents’ combined income, using a schedule, and then split that cost between the parents in proportion to their incomes. As a labeled illustration only, not any state’s schedule: if one parent earns 40% of the combined income and the other 60%, the first is responsible for 40% of the schedule amount and the second for 60%. The parent who has the child most of the time is assumed to spend their share directly, so the other parent pays theirs.
What income counts
Federal rules require every guideline to consider all earnings and income of the noncustodial parent and, at the state’s discretion, the custodial parent. They also require a low-income adjustment, such as a self-support reserve, for a parent with limited ability to pay, and say that if a state allows imputing income, it must weigh the parent’s circumstances, including assets, work history, health and the local job market. Incarceration may not be treated as voluntary unemployment. The details of what counts as income, and what can be deducted, are set state by state.
Child care, health care and other add-ons
The base amount is rarely the whole bill. The NCSL notes that most guidelines add special amounts for child care expenses and make deductions for supporting previous and subsequent children. The federal rule also requires every guideline to address how the parents will provide for the child’s health care needs, through private or public coverage or cash medical support. Check how your state treats child care, health insurance and extraordinary expenses before you rely on a base figure.
How parenting time changes the number
Many guidelines have a special formula once both parents have the child for a meaningful share of the year, and the cutoff differs. Virginia, for example, applies its shared custody formula when a parent has custody or visitation more than 90 days of the year, while Wyoming applies its shared responsibility formula above 25% of overnights when both parents also contribute substantially to expenses. The guidelines also have special rules for split custody, where each parent has some of the children. Count your overnights with the Parenting Time Calculator, and see what the custody terms mean.
When a court can depart from the guideline
The guideline amount is presumed correct, but not final. Under federal law a written finding, or a specific finding on the record, that applying the guideline would be unjust or inappropriate in a particular case is enough to rebut the presumption, under criteria the state sets. Guidelines are also reviewed at least every four years, so schedules and thresholds change. When circumstances change after an order, see whether you can modify child support and when child support ends.
How to find your number
Pick your state in the Child Support Calculator, enter both incomes and the schedule, and compare the result with your order. If you are weighing a change, the Child Support Modification Calculator shows whether it meets your state’s threshold, and the Child Support End Date Calculator shows when the obligation ends. The family law calculators cover every state, and our methodology page explains how each figure is verified. For advice on your own case, talk to a licensed family law attorney in your state.