How Child Support Is Calculated
Child support formulas aim to ensure children maintain a similar standard of living to what they'd have if both parents lived together. Every U.S. state uses one of three calculation models, and the numbers vary widely. A parent earning $60,000 in Texas (percentage-of-income state) pays a different amount than a parent earning $60,000 in California (income shares state) for the same number of children.
All states start with gross or net income, then apply a formula based on the number of children. From there, adjustments kick in for health insurance, childcare costs, extraordinary expenses (medical, educational), and the amount of time each parent spends with the children.
Three Child Support Models Explained
Income Shares Model (used by 41 states): Both parents' incomes are combined to estimate what the household would have spent on the children. That obligation is then divided proportionally by each parent's income. If Parent A earns 65% of combined income, they owe 65% of the child support obligation. The custodial parent's share is assumed to be spent directly on the child.
Percentage of Income Model (used by Texas, Wisconsin, Mississippi, and a few others): Only the non-custodial parent's income matters. A flat percentage is applied: 17% for one child, 25% for two, 29% for three, 31% for four, and at least 35% for five or more. Simple to calculate, but it ignores the custodial parent's income entirely.
Flat Rate / Melson Formula (used by Delaware, Hawaii, Montana): A variation that first ensures each parent can meet their own basic needs, then allocates a percentage of remaining income to child support. It accounts for self-support reserves before calculating the obligation.
How Custody Time Affects Child Support
More parenting time typically reduces child support obligations. The logic: you're directly spending on the child during your overnights (food, housing, activities), so the cash transfer should be lower. Most states apply a parenting-time credit when the non-custodial parent exceeds a threshold — usually around 90 to 110 overnights per year (roughly 25–30% of the year).
In a 50/50 custody arrangement, child support doesn't disappear. The higher-earning parent still typically pays support to equalize the children's standard of living between households. The amount is just significantly lower than in a standard every-other-weekend arrangement.
When to Consult a Family Law Attorney
Online calculators give you a starting point, not a court order. Consult an attorney when: you have complex income (business ownership, stock options, irregular commissions), one parent is voluntarily unemployed or underemployed, children have special medical or educational needs, you're modifying an existing order due to changed circumstances, or you're dealing with interstate custody where different state formulas may apply.
Most state court websites publish their official child support worksheets for free. Your state's child support enforcement agency can also run an official calculation at no cost. Use this calculator to understand the ballpark, then get official numbers from your state's tools or a licensed attorney.
For tracking shared child expenses after support is set, use our co-parenting expense calculator. To understand how custody schedules break down by overnights, try the parenting time calculator. If you're also dividing assets, see our divorce asset split calculator.