Topic guide · updated 2026-08-02
How child support is actually calculated
Every state sets child support from a published guideline formula, and there are only four of them in use across the country. This explains which model your state uses, what income figure it counts, and why two families with identical incomes can owe different amounts.
There is a widespread belief that child support is set by a judge weighing what seems fair. It is not. Every state publishes a guideline formula, applies it to income figures its own statute defines, and treats the result as presumptively correct — a judge departs from it by explaining why, on the record.
That makes the whole thing far more knowable than it looks. If you can find out which model your state uses and what it counts as income, you can compute the same number the court starts from.
What you cannot do is predict an order. Guidelines are presumptive, not binding, and the income figures a court establishes may not match the ones you estimate. Everything below is the arithmetic, not the outcome.
There are four models, not fifty
Most states use income shares: a published table gives the amount both parents together would be expected to spend on a child at their combined income, and that amount is divided between them in proportion to what each earns. A minority use percentage of income, which takes a fixed share of the paying parent's income and does not consider the other parent's income at all. Texas is the largest example. Delaware, Hawaii and Montana use the Melson formula, which reserves a self-support allowance for each parent before calculating anything for the children, then adds a standard-of-living adjustment on top. California sits on its own with a statutory algebraic formula in Family Code section 4055, which builds parenting time directly into the equation.
The income figure is not your take-home pay
Every model runs on an income definition its statute sets out, and none of them is the number on your payslip. Texas computes net resources by subtracting a fixed list — social security taxes, federal income tax calculated as though you were single with one exemption, state income tax, union dues, and the child's health insurance. A mortgage is not on the list. Neither is a car payment. California works from net disposable income under a separate code section with its own deduction list. Many income shares states use gross income instead. The practical consequence is that two people taking home the same amount each month can have materially different guideline figures, and that a support number can look higher than what someone feels they actually have.
Parenting time changes the answer in some states and not others
California's formula includes a timeshare percentage, so every additional overnight moves the number continuously. Many income shares states adjust only once parenting time crosses a published threshold. That produces a cliff: one night either side of the threshold can change an order substantially, and nights well away from it change nothing at all. Some guidelines make no adjustment for overnights whatsoever, though a court may still treat parenting time as a reason to depart from the guideline figure. Because guidelines count overnights rather than hours, a parenting calendar is the evidence that matters — and a schedule built from a standard rotation gives you a defensible count before holidays and summer are layered on.
What the guideline number is and is not
It is the output of a published formula applied to the figures you entered. That is genuinely useful: it is where a negotiation or a hearing starts, and being wrong about it by a wide margin is a bad position to be in. It is not a prediction. Courts retain discretion, every state's statute lists reasons to deviate, and the income figures a court establishes in a contested case can differ from an estimate. It also says nothing about arrears, tax treatment, health insurance orders, or how support interacts with custody. Those are questions for a lawyer licensed where you live.
Tools in this topic
Every calculator and explainer in this cluster, each built on verified figures with its official source linked.
Guides
What Texas counts as net resources
Texas applies its child support percentages to net resources, a figure its Family Code defines with a closed list of deductions. It is not gross pay and it is not take-home pay, and the difference changes the guideline number.
How parenting time enters California's support formula
California puts timeshare directly into its statutory child support equation, so every overnight moves the number. This explains where the timeshare term sits in Family Code section 4055 and why its effect is larger than it looks.
Key terms
Frequently asked questions
Parents can generally propose an agreed figure, but a court reviews it against the guideline and in most states must be satisfied that departing from the guideline is appropriate. The guideline number therefore still matters even where everyone agrees, because it is the benchmark the agreement is measured against.
Official sources for this topic
Every figure and rule referenced above is published by one of these agencies, and each of them — not this site — determines what is actually paid.
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