The Basic Formula: Income and Custody Time

Child support is calculated using a formula that combines both parents' income and how much time each parent spends with the child. The exact formula varies by state, but nearly all states use one of three models: the income shares model, the percentage of income model, or the flat percentage model. Most states use income shares, which divides support obligations based on each parent's share of total household income.

The starting point is always the same: the court or child support office adds up both parents' monthly gross income. This includes wages, salary, self-employment income, bonuses, rental income, and sometimes Social Security or disability payments. The court then determines what percentage of the total income each parent earns. If one parent makes $3,000 per month and the other makes $2,000, the first parent is responsible for 60 percent of the support obligation and the second for 40 percent.

Next, the court looks at custody time. Most states define this as the number of overnights each parent has per year. If one parent has the child 70 percent of the time and the other 30 percent, that affects how much the lower-income parent pays. The parent with less custody time usually pays more support because the other parent is covering more of the day-to-day costs.

Key Takeaways

  • Child support is calculated by combining both parents' gross income and the percentage of time each parent spends with the child.
  • The formula varies by state, but most use the income shares model, which divides the obligation based on each parent's percentage of total income.
  • Income includes wages, self-employment earnings, bonuses, rental income, and sometimes government benefits — not just a paycheck.
  • The parent with less custody time typically pays more support, because the other parent covers more daily expenses.
  • Child support orders can be modified if either parent's income changes significantly or custody arrangements change.

What Counts as Income

Income for child support purposes is broader than just a regular paycheck. Courts include W-2 wages, self-employment income, bonuses, commissions, rental income from property, interest and dividend income, and income from retirement accounts. Some states also count Social Security benefits, workers' compensation, unemployment benefits, and disability payments.

Self-employed parents often face closer scrutiny. The court may look at tax returns for the past two or three years and may adjust income up or down based on business expenses, depreciation, and whether income appears to be artificially low. If a parent owns a business, the court may hire an accountant to review the books.

Income that does not count includes child support received from another child, means-tested benefits like TANF or SNAP, and tax refunds. Some states exclude overtime income or income from a second job if the parent can show it is temporary or seasonal.

How States Calculate the Actual Dollar Amount

Once the court knows both parents' income and custody time, it looks up the state's child support guideline table. This table shows the base support obligation for different income levels and custody arrangements. For example, a state's table might show that for combined parental income of $5,000 per month with one child and standard custody (70/30 split), the total obligation is $900 per month.

The court then divides that obligation between the parents based on their income percentages. If one parent earns 60 percent of the combined income, that parent pays 60 percent of the $900 obligation, or $540. The other parent pays $360. However, the parent with primary custody (70 percent) usually does not write a check — instead, the other parent pays the full amount directly to that parent or through the state's child support collection system.

The guideline table itself changes by state and is updated periodically. Some states adjust it every four years; others do so less frequently. The table also accounts for the number of children — support for two children is higher than for one, but not double.

Adjustments for Special Circumstances

The guideline amount is a starting point, not always the final order. Courts can adjust support up or down based on factors like childcare costs, health insurance premiums, extraordinary medical expenses, and the cost of the child's education. If one parent pays for the child's private school tuition or has significant out-of-pocket medical bills, the court may increase support to account for those costs.

Courts also adjust for situations where one parent has a very high income. Many states cap the income used in the calculation — for example, only counting income up to $150,000 per year — to prevent support from becoming unreasonably high. Some states allow the court to go above the cap if the child's standard of living before the separation was very high.

Other adjustments include time spent with the child (if custody is close to 50/50, support may be lower), the cost of health insurance and childcare, and whether either parent is supporting other children from a different relationship. A parent paying support for two other children may have their obligation reduced.

How Custody Time Affects the Amount

Custody time is measured in overnights per year. If one parent has the child 182 overnights or fewer, that parent is considered to have less than 50 percent custody. If both parents have roughly equal time — say, 180 to 185 overnights each — the support calculation changes significantly. In some states, the parent with slightly less time still pays, but the amount is much lower. In others, the obligation may swing back and forth depending on which parent earns more.

The reason is that when a parent has the child overnight, that parent is paying for food, utilities, and housing for that child. If both parents split time equally, both are covering those costs, so support is lower than if one parent has the child 80 percent of the time.

Custody time also includes school breaks, holidays, and summer vacation. A parent who has the child for the entire summer may have more than 50 percent of overnights even if the school-year schedule favors the other parent. The court counts actual overnights, not just the regular school-year schedule.

Changes in Income and Custody

A child support order is not permanent. Either parent can request a modification if income changes by a certain amount — usually 10 to 15 percent, though this varies by state — or if custody arrangements change. If a parent loses a job, gets a significant raise, or changes from part-time to full-time work, that is grounds to ask the court to recalculate.

The parent requesting the change must file a motion with the court or contact the child support enforcement office. The court will review the new income and custody information and issue a new order. The change usually takes effect on the date the motion is filed, not the date the order is signed, though some states have different rules.

If a parent deliberately reduces income to lower support — for example, by quitting a job or turning down a promotion — the court may impute income, meaning it assigns income to that parent based on what they could earn. The court looks at the parent's work history, education, and local job market to decide what income to assign.

Frequently Asked Questions

Does child support include money for activities like sports or music lessons?

Not automatically. The base child support amount covers basic living expenses. However, if the child was enrolled in activities before the separation, the court may order one or both parents to split the cost as an add-on to support. This is separate from the main support calculation and requires a specific court order.

What happens if a parent is unemployed or disabled?

The court does not automatically reduce support to zero. If a parent is unemployed, the court may impute income based on their work history and earning capacity. If a parent is disabled and receiving Social Security, the court may count that as income. The parent must show the court that the unemployment or disability is genuine and not a deliberate attempt to avoid support.

Can child support be calculated differently if parents share custody equally?

Yes. When custody is close to 50/50, most states use a different calculation that accounts for both parents covering daily expenses. The support amount is usually much lower than in cases where one parent has primary custody. Some states use a formula that reduces the obligation based on the percentage of overnights; others calculate it differently.

Does the child support amount change when the child turns 18?

Usually, yes. Most states end child support when the child turns 18 or graduates from high school, whichever is later. Some states extend it to age 19 or 20 if the child is still in high school. The parent paying support does not need to file a motion to stop — the order ends automatically on the date specified in the order.

How do I find out what my state's guideline table is?

Your state's child support enforcement office publishes the guideline table on its website. You can also ask the court clerk or contact a family law attorney. The table is public information and shows the base obligation for different income levels and numbers of children.