How Child Support Is Calculated: State Formulas, Income Factors, and What You Can Expect to Pay or Receive

Child support in the US is calculated using one of three models: the Income Shares Model (41 states), the Percentage of Income Model (6 states), or the Melson Formula (Delaware, Hawaii, and Montana). Both produce a monthly dollar amount that the non-custodial parent (or the parent with less custody time) pays to the other parent. The Income Shares Model (most states): combines both parents' gross incomes, looks up the total on a state-specific chart that estimates how much a family at that income level spends on children, then divides the obligation proportionally based on each parent's share of the combined income. If Parent A earns $60,000 and Parent B earns $40,000 (combined $100,000), Parent A is responsible for 60% of the child support obligation and Parent B for 40%. The table might say a family earning $100,000 with 2 children spends approximately $1,800/month on the children. Parent A's share: $1,080/month. Parent B's share: $720/month. If Parent B has primary custody, Parent A pays Parent B $1,080/month. The Percentage of Income Model (6 states: Alaska, Mississippi, Nevada, North Dakota, Texas, Wisconsin): simpler — a flat percentage of the non-custodial parent's income. Texas, for example: 20% of net income for 1 child, 25% for 2, 30% for 3. If the non-custodial parent earns $5,000/month net, child support for 1 child is $1,000/month. Anew estimates child support from both incomes, the number of children, and parenting time using your state's general approach, and can explain the numbers in plain English. This content is for educational purposes only and does not constitute legal advice. Consult a family law attorney for your specific situation.

Courts define income broadly for child support purposes — much broader than just your W-2 salary. All of the following are typically included: gross wages and salary (before taxes — not take-home pay), overtime and bonuses (averaged over 2-3 years if variable), self-employment net income (revenue minus legitimate business expenses — but courts add back aggressive deductions like vehicle depreciation and personal expenses run through the business), rental income, investment income (dividends, interest, capital gains), retirement income (pension, Social Security, 401k distributions), disability benefits (workers' comp, SSI, SSDI), unemployment benefits, alimony received from a prior marriage, military allowances (BAH, BAS), and trust distributions. What is typically NOT included: means-tested public benefits (SNAP, Medicaid, TANF), child support received for other children, income of a new spouse (in most states — some allow it as a factor in deviation requests), and one-time windfalls (insurance settlements, inheritance — though some courts consider these). The self-employment trap: self-employed parents who minimize taxable income through aggressive deductions often find that the court imputes higher income for child support. If your tax return shows $50,000 in income but your lifestyle reflects $120,000 in spending, the court may use the lifestyle analysis to determine your actual income. Business depreciation, personal vehicle expenses, home office deductions, and meals/entertainment are commonly added back. Imputed income: if a parent is voluntarily unemployed or underemployed (quit their job to reduce child support, or works part-time when capable of full-time), the court can impute income — calculate child support based on what the parent could earn rather than what they actually earn. This is based on the parent's education, work history, skills, and the local job market. Anew can write a custom checklist of the income sources to document.

In Income Shares states, the custody time split directly affects the child support calculation. The more time the non-custodial parent has, the lower the child support payment — because they are covering the child's expenses directly during their custody time. Most states use an overnight count: the number of overnights each parent has per year. A standard custody arrangement might be 80/20 (custodial parent has 292 overnights, non-custodial has 73). A 50/50 arrangement is 182.5 each. The overnight count feeds into the formula, typically through a time-sharing adjustment that reduces the non-custodial parent's obligation as their time increases. The tipping point: many states adjust support once the other parent's overnights reach a threshold set by state law, and the threshold varies (Illinois applies its shared-care formula when each parent has 146 or more overnights a year). Below the threshold, the standard formula applies with minimal adjustment. Above it, a shared-parenting formula kicks in that substantially reduces the obligation because both parents are incurring direct expenses for the children. This is why custody and child support are intertwined — a parent who fights for more custody time is also reducing their child support obligation. Courts are aware of this and evaluate whether the request for additional time is genuinely about the children or is financially motivated. A parent who has been uninvolved for years suddenly requesting 50/50 custody coincident with a child support filing raises judicial skepticism. 50/50 custody does NOT mean zero child support. In most states, even with equal time, the higher-earning parent pays some support to the lower-earning parent because the children's standard of living should be similar in both homes. If Parent A earns $150,000 and Parent B earns $50,000, with 50/50 custody, Parent A will still pay support — typically a reduced amount compared to the standard formula, but not zero. In Anew's child support estimate, you can move the overnights slider to see how parenting time changes the estimate.

The calculated amount from the state formula is the presumptive amount — the starting point. Courts can deviate upward or downward based on specific circumstances. Common grounds for upward deviation: extraordinary medical expenses for the child (chronic conditions, therapy, special needs), private school tuition that both parents agreed to, high-income situations where the state table caps out (many state tables stop at a set combined income, and above that the court has discretion), and significant travel costs for long-distance visitation. Common grounds for downward deviation: extraordinary expenses borne by the paying parent (supporting other biological children, high medical costs), significant debt obligations from the marriage (mortgage on the marital home being maintained for the children), and genuine hardship where the formula amount would reduce the paying parent below a self-support threshold. Modification: child support orders can be modified when there is a substantial change in circumstances — not just because one parent wants a different number. Qualifying changes: significant income increase or decrease (some states set a numeric test, such as a 15% change in either parent's income in New York), change in custody arrangement, child's needs have changed (medical, educational), loss of job (if involuntary — voluntary job loss may result in imputed income instead of modification), and new children (some states consider additional children born to the paying parent). The modification process: file a motion with the court that issued the original order. Provide evidence of the changed circumstance. The court recalculates using the same formula with updated numbers. Modification is not retroactive — it takes effect from the date of filing, not from the date the change occurred. This means if you lose your job in January but do not file for modification until June, you owe the original amount for January through June. Anew's coach can explain how support modification generally works, and you can rerun the child support estimate with new incomes to see a rough new number before you talk to an attorney.