Child support is not freely negotiated between parents the way dividing furniture might be. Every state sets a formula-based guideline, and courts must follow it unless specific circumstances justify a deviation. That means the starting point for any child support conversation is always the state's calculation model — not an agreement made at the kitchen table.
Federal law requires all states to have a formula-based system, but what varies considerably is the formula itself, how income is defined, and how much room judges have to stray from the result. This guide explains how the two dominant models work, what goes into the income calculation, how custody time affects the outcome, and what you can realistically expect as a monthly figure.
The Two Main Models States Use
Income Shares Model (About 40 States)
The income shares model is used in roughly 40 states and starts from a straightforward premise: a child should receive the same share of combined parental income they would have received if the parents had stayed together.
The calculation follows a defined sequence. First, both parents' gross monthly incomes are added together. Second, a state-published schedule assigns a basic child support obligation based on that combined income and the number of children. Third, each parent's proportional share of the combined income determines their share of the obligation. The noncustodial parent pays their share directly to the custodial parent; the custodial parent's share is presumed spent directly on the child.
Example: Parent A earns $5,000/month; Parent B earns $3,000/month. Combined income is $8,000. The state schedule sets $1,200/month for one child at that income level. Parent A, who earns 62.5% of combined income, would owe $750/month.
Percentage of Income Model (About 10 States, Including Texas)
A smaller group of states — including Texas, Wisconsin, and Alaska — use the percentage of income model. Support is a fixed percentage of the paying parent's net income, regardless of the receiving parent's earnings. The result is easier to calculate, but it does not factor in the custodial parent's ability to contribute.
Texas percentages are among the most widely referenced: 20% of net monthly income for one child, 25% for two children, 30% for three, 35% for four, and 40% for five or more, subject to statutory caps. Other percentage-of-income states use similar structures but with different rates and ceiling amounts.
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Use the Free CalculatorWhat Counts as Income
Courts define income broadly for child support purposes. Nearly every regular source of money qualifies, not just wages. Common income categories that factor into the calculation include:
- Wages, salary, tips, and commissions
- Bonuses and overtime pay
- Self-employment income, net of legitimate business expenses
- Rental income from property
- Investment returns — dividends, interest, capital gains
- Unemployment compensation
- Pension and retirement distributions
- Workers' compensation and disability benefits
Means-tested public assistance — SNAP, Medicaid, SSI — is generally excluded. Courts can also impute income to a parent who is voluntarily unemployed or underemployed without justification, assigning earning capacity rather than actual earnings.
What Gets Deducted Before the Calculation
Several items reduce the income figure used in the formula before a guideline amount is set:
- Existing court-ordered child support for other children. Payments already being made for children from another relationship are typically deducted from gross income first.
- Health insurance premiums for the child. The portion of a parent's insurance premium attributable to the child is subtracted and then factored into the support order separately.
- Work-related childcare costs. Daycare, after-school care, or other employment-related childcare expenses are usually added on top of the base obligation and split proportionally between parents — which has the effect of reducing the net out-of-pocket cost for the parent who pays them upfront.
How Custody Time Affects the Payment
In most income shares states, the basic obligation assumes one parent has primary physical custody and the other has standard parenting time. When the noncustodial parent has substantially more time — typically 30% or more of overnight visits, often cited as around 110 nights per year — a parenting time adjustment reduces the base obligation.
The logic: when a parent has the child for a significant portion of nights, they incur direct costs (food, shelter, clothing, activities) that would otherwise be assumed to fall exclusively on the custodial parent. The adjustment credits those costs against the monthly transfer. The exact threshold and reduction amount vary by state. Some states apply the adjustment on a sliding scale; others apply a flat reduction at a defined overnight threshold.
Custody time adjustments can have a meaningful impact on the final figure, which is one reason parenting schedules and support calculations are often negotiated together.
Healthcare and Add-On Expenses
Most states treat certain child-specific expenses as add-ons rather than building them into the base obligation. These are calculated separately and split between parents in proportion to their incomes:
- The child's share of health insurance premiums
- Uninsured and unreimbursed medical expenses above a threshold (often $250 per year per child)
- Work-related childcare costs
- Extraordinary educational expenses, in some states
This means the total monthly obligation to the custodial parent is often higher than the base guideline figure alone. Tracking and documenting these add-on expenses is important because disputes over them are common.
Sample Monthly Estimates by Income and Children
The figures below illustrate typical income shares outcomes. These are approximations — actual amounts depend on your state's specific schedule, any applicable deductions, and judicial discretion. Do not use this table for legal or financial planning without confirming your state's current guidelines.
| Non-Custodial Parent's Monthly Income | 1 Child | 2 Children | 3 Children |
|---|---|---|---|
| $2,500 | ~$300 – $375 | ~$450 – $530 | ~$560 – $640 |
| $4,000 | ~$450 – $560 | ~$640 – $760 | ~$780 – $920 |
| $6,000 | ~$620 – $760 | ~$880 – $1,050 | ~$1,060 – $1,250 |
| $8,000 | ~$780 – $950 | ~$1,080 – $1,280 | ~$1,290 – $1,520 |
| $12,000 | ~$1,050 – $1,260 | ~$1,400 – $1,680 | ~$1,700 – $2,000 |
When Courts Deviate From the Guideline
A state guideline figure is a presumption, not an absolute. Judges can deviate upward or downward when the standard calculation would be unjust or inappropriate given specific facts. Deviation requires written findings in the court order explaining the basis. Common grounds include:
- A child with significant special needs or chronic medical conditions
- Income far above the guideline schedule's top cap (high-income cases use judicial discretion above a ceiling)
- A parent who traveled extensively for work and incurred unusual child-related expenses
- An older child with substantially higher costs than the standard schedule reflects
- A parent's non-cash contributions to the child's welfare that offset the guideline obligation
When Support Ends — and How to Modify It
Child support ends at a statutory age set by state law. Most states terminate at age 18. Many extend to 19 if the child is still enrolled in high school. A handful of states — including New York (age 21) and a small group that permit college support orders — have later end dates. Early termination can occur if the child marries, enters active military service, or is legally emancipated.
Modification is available when circumstances change substantially. Most states define "substantial" as a 15–20% shift in the guideline amount, though the exact threshold varies. Common triggers for modification petitions include:
- A significant income increase or decrease for either parent
- Involuntary job loss or reduction in hours
- A material change in the child's needs or custody arrangement
- The paying parent incurring a new child support obligation for another child
Know Your Number Before You Negotiate
Run a free estimate with your income, custody split, and number of children — so you have a defensible starting point before any discussion or court filing.
Calculate Child Support NowChild support law is state-specific. The rules summarized here reflect common patterns across jurisdictions, but your state's schedule, income definitions, and deviation standards may differ. An attorney in your state or your state's child support enforcement agency can provide a precise calculation based on your actual numbers. This page is educational only and does not constitute legal advice.