This guide is general legal information, not legal advice, and does not create an attorney–client relationship. Rules change and vary by state — verify current requirements with official sources or a licensed attorney.
Child support in the United States is not left to a judge's gut feeling. Federal law requires every state to maintain numeric guidelines that produce a presumptively correct support amount, and a court that departs from the number must explain why in writing. So the practical questions for any parent are: which formula does my state use, what goes into it, and what does it take to change the result later?
This guide walks through the three guideline models states use, the income and expense inputs that drive the number, and the federal and state rules for reviewing and modifying an order once it exists.
Key takeaways
- Every state must use guidelines that create a rebuttable presumption of the correct support amount; deviations require written findings (45 CFR § 302.56).
- Most states use the income shares model; a handful, including Texas, use a percentage-of-income model; Delaware, Hawaii, and Montana use the Melson formula.
- "Income" is defined broadly, and courts can impute income to a parent who is voluntarily unemployed or underemployed — but incarceration may not be treated as voluntary unemployment.
- Orders in state child-support-agency cases must be reviewable at least every three years on request; earlier changes generally require a substantial change in circumstances.
- Modifications are prospective: past-due amounts generally cannot be retroactively reduced, so seek review as soon as circumstances change.
A federal floor, fifty state formulas
Congress conditioned federal child-support funding on state guideline systems, and the implementing regulation, 45 CFR § 302.56, sets the floor. Each state must adopt one statewide set of guidelines, base orders on the noncustodial parent's earnings and ability to pay, address the child's health-care coverage, include adjustments for low-income parents, and review its guidelines against current economic data at least every four years.
Within that framework, states chose their own math. The amount ordered for the same family can differ meaningfully across state lines — which is why support questions during a divorce are inseparable from the state where the case is filed, as our overview of how divorce works in the United States explains.
The three guideline models
According to a National Child Support Engagement Association summary, the large majority of states use income shares, about six use percentage-of-income, and three use the Melson formula.
| Model | Core idea | Whose income counts | Representative states |
|---|---|---|---|
| Income shares | Estimate what the parents would have spent on the child in an intact household, then split that amount in proportion to each parent's income. | Both parents | Used by roughly 40 states, including Illinois, Ohio, and Virginia |
| Percentage of income | Apply a flat or varying percentage to the paying parent's income, scaled by the number of children. | Primarily the noncustodial parent | Texas and Wisconsin, among a few others |
| Melson formula | Reserve a self-support amount for each parent and cover the child's basic needs first; the child then shares a portion of any additional income. | Both parents | Delaware, Hawaii, Montana |
Income shares in practice
An income shares state combines both parents' incomes, looks up a basic support obligation in an economic table, and allocates it pro rata. If the parents together earn $10,000 per month and the paying parent earns 60 percent of that, the paying parent covers 60 percent of the table amount, usually adjusted for parenting time, health-insurance premiums, and child-care costs. Many states publish official online calculators or worksheets — use your state's, not a generic one.
Percentage of income in practice
Texas illustrates the percentage model. Guideline support starts at 20 percent of the paying parent's monthly "net resources" for one child, stepping up with additional children, and the guideline percentages apply only up to a statutory cap on net resources — $11,700 per month under the adjustment effective September 1, 2025. Above the cap, additional support requires proof of the child's needs. Details and current figures are on the Texas Attorney General's child support pages.
What counts as income — and what gets imputed
Guideline "income" reaches well beyond a base salary. States commonly count wages, overtime, bonuses, commissions, self-employment earnings, rental income, unemployment and disability benefits, and investment returns. Self-employed parents' income is often the most contested input, because business deductions appropriate for taxes are not always allowed for support purposes.
When a parent earns less than they could by choice, courts can impute income — calculate support as if the parent earned what their education, work history, and local job market support. Federal rules add two guardrails: guidelines must consider a low-income parent's basic subsistence needs, and incarceration may not be treated as voluntary unemployment when setting or modifying an order.
Practical note: Support and parenting time interact in many state formulas — more overnights can lower the transfer payment. But the schedule itself is set under the best-interests custody standard, and courts react badly to parenting-time requests that look like support-reduction strategies.
Add-ons and deviations
On top of the base amount, orders typically allocate health-insurance premiums, unreimbursed medical costs, and work-related child care; many states also address private school or extracurricular expenses. The guideline number is a rebuttable presumption: a judge may deviate up or down — for extraordinary medical needs, shared-parenting arrangements, or other listed reasons — but must state in writing why the guideline amount would be unjust or inappropriate in that case.
Changing an order: review and modification
Support orders are built to be revisited. The federal Office of Child Support Services describes two tracks for cases handled by state child-support agencies:
- Request a review. In agency-enforced cases, states must notify parents at least every three years of the right to request a review of the order. Within that three-year cycle, an adjustment to match current guideline amounts generally does not require proof of changed circumstances.
- Show changed circumstances for earlier review. Outside the regular cycle — or in private (non-agency) cases in many states — the requesting parent must demonstrate a substantial change in circumstances, such as involuntary job loss, a significant income change, a new child's needs, disability, or incarceration.
- Agency or court recalculates. The reviewing authority applies current guidelines to current financial information. The order may go up as easily as down; some states also require the difference to exceed a threshold (for example, a set percentage or dollar amount) before an adjustment issues.
- New order takes effect prospectively. Changes generally date back no earlier than the filing of the modification request. Support that accrued before then remains owed.
Watch the deadline: Federal policy generally prohibits retroactive reduction of arrears that accrued before a modification request was filed. A parent who loses a job and waits a year to seek modification will usually owe the full original amount for that year — file promptly and keep paying what you can.
When payments stop: enforcement basics
Unpaid support does not fade away. State agencies can collect through income withholding from paychecks, interception of federal and state tax refunds, liens, credit-bureau reporting, and suspension of driver's, professional, and recreational licenses; passport denial is available for large federal arrears. Willful nonpayment can lead to contempt proceedings. Because enforcement tools are largely automatic once an order exists, parents in financial trouble are almost always better off seeking a modification than silently falling behind.
Support obligations also outlast many other divorce terms. Property division is typically final once entered — see our comparison of community property and equitable distribution — while child support remains adjustable until it terminates, usually at the age of majority or high-school graduation, later for adult children with disabilities in many states.
Frequently asked questions
Can parents simply agree on a child support amount?
Parents can propose an agreed amount, but a court must approve it, and most states require the order to reference the guideline calculation and justify any deviation. Support is legally the child's right, so parents generally cannot waive it outright or trade it away in negotiations, even in an otherwise uncontested divorce.
Does remarriage change child support?
A new spouse's income is generally not counted as the parent's income for guideline purposes, though a few states allow limited consideration of household circumstances. What more often triggers review is a change in the parent's own income or the birth of additional children, which many states treat as a factor or credit in the formula. State rules differ, so check yours.
Is child support taxable or deductible?
No on both counts under federal law: child support is not income to the recipient and not deductible by the payer. That distinguishes it from some spousal-support arrangements and makes the pre-tax versus after-tax character of the guideline inputs — gross income in some states, net in others — an important detail in calculations.
What if the other parent lives in another state?
The Uniform Interstate Family Support Act, adopted in every state, governs which state's courts control the order and prevents competing orders. Generally the state that issued the order keeps exclusive authority to modify it while a parent or the child still lives there, and other states must enforce it as written. Interstate cases benefit from early legal advice.
Keeping the number current
The guideline number is only as accurate as the information behind it, and family finances rarely stand still. Treat a support order as a living document: keep records of income changes, insurance premiums, and child-care costs; calendar the three-year review right if a state agency services your case; and act quickly when a real change hits, because relief rarely reaches back before your filing date. For the surrounding legal landscape — custody, property, and process — our family and divorce law topic hub collects the related guides. This article is general information, not legal or tax advice; a family-law attorney or your state child-support agency can run your state's actual numbers.
Sources & further reading
- HHS Office of Child Support Services — How is child support determined?
- HHS Office of Child Support Services — How is a child support order changed?
- 45 CFR § 302.56 — Guidelines for setting child support orders (LII)
- Texas Attorney General — Support Modification Process
- NCSEA — Quick Facts: Child Support Guidelines
