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How Child Support Is Calculated in the US (2026)

Child support in the United States is determined by state-specific statutory guidelines — not individual judge discretion. Courts must follow these guidelines unless there is a documented reason to deviate. Every state uses one of three formula models, each with a different approach to determining the base monthly obligation.

The Income Shares Model (Used by ~41 States)

The Income Shares model is the most widely used approach. The core idea is simple: how much would this couple have spent on the child if they had stayed together? That hypothetical amount becomes the "basic child support obligation," and each parent is responsible for their proportional share of that total based on their income.

How it works in practice: Both parents' gross monthly incomes are combined. State guideline tables then specify what percentage of that combined income should go toward child support, broken down by number of children (roughly 17% for 1 child, 25% for 2, 29% for 3, 31% for 4, and 34% for 5+). The paying parent contributes their proportional share of that obligation. Custody time, health insurance premiums paid for the child, and work-related childcare costs are then layered on top of this base calculation.

States using Income Shares include: Alabama, Arizona, California, Colorado, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Utah, Vermont, Virginia, Washington, and West Virginia.

The Percentage of Income Model (Used by ~6 States)

In Percentage of Income states, the formula is simpler: the court applies a fixed percentage directly to the paying parent's income, regardless of what the other parent earns. The percentages are based on the number of children: 17% for 1 child, 25% for 2, 29% for 3, 31% for 4, and 34% for 5 or more.

Texas, for example, uses this model — with the percentage applied to the paying parent's net income (after taxes and certain deductions) rather than gross income. Wisconsin uses a similar percentage-of-income approach. States using this model include: Alaska, Arkansas, Mississippi, North Dakota, New Hampshire, Texas, Wisconsin, and Wyoming.

The Melson Formula (Delaware, Hawaii, Montana)

The Melson Formula is a more complex variant of the Income Shares model used in Delaware, Hawaii, and Montana. It first ensures each parent retains a minimum subsistence reserve — enough income to meet their own basic needs — before calculating what's available for child support. It then applies a "standard of living adjustment" (SOLA) to share any remaining income with the child. In practice, Melson Formula results are very close to Income Shares for middle-income families; the difference is most pronounced at low income levels.

What Factors Affect Child Support?

Beyond the base formula, these factors commonly modify child support orders:

• Custody split: The single biggest variable. More overnight parenting time for the paying parent = lower support. A 50/50 split can reduce the base obligation by 30–50% in most states.
• Health insurance: The cost of covering the child on a health insurance plan (the child's incremental share of premium) is typically added to the base support and split proportionally.
• Childcare costs: Work-related childcare expenses (daycare, after-school care) are split proportionally between parents based on income in most states.
• Extraordinary medical expenses: Unreimbursed medical, dental, and mental health costs above a threshold are typically split proportionally.
• Special needs: Children with disabilities, chronic conditions, or special educational needs may have higher support orders reflecting those actual costs.
• Other children: If either parent is legally obligated to support children from other relationships, that may reduce their available income for this calculation.
• Income caps: Most states' guideline tables cap at a combined income of $10,000–$30,000/month. Above the cap, courts have discretion and typically look at actual expenses.

Child Support by State — All 50 States (2026)

Formula model, approximate percentage for 2 children at median income, and whether the state provides an official online calculator. Use this as a research starting point — always verify with your state's official guidelines.

Sources: State court administrative offices, HHS Office of Child Support Services (OCSS), National Conference of State Legislatures (NCSL). Percentages are approximations at median combined income — actual tables vary by income bracket. Updated August 2026.

Can Child Support Be Modified?

Yes — and this is one of the most frequently asked questions in family law. Courts recognize that life circumstances change, and most states allow either parent to petition for a modification when there has been a "substantial change in circumstances" since the last order was entered.

What Qualifies as a Substantial Change?

• Income change: Most states define "substantial" as a 15–25% change in either parent's income. A job loss, significant raise, new job, or disability can all trigger review eligibility.
• Custody change: If the custody arrangement changes significantly — say, from primary custody to shared 50/50 — the support formula must be recalculated. This is especially important when the change results in one parent exercising significantly more overnights.
• Child's changing needs: A child who develops a medical condition, begins attending private school by court order, or ages out of childcare may trigger modification.
• Automatic review: Many states (especially where one parent receives public assistance) conduct mandatory reviews every three years. You can request a review without proving a substantial change in these situations.

Critical Rules on Modifications

Modifications are never retroactive. Even if your circumstances changed six months ago, a modification only takes effect from the date you filed your petition with the court — not from when circumstances changed. This is why you should file a modification petition immediately if your income drops significantly, rather than waiting to see how things play out.

Do not stop paying while waiting. The existing court order remains legally binding until a new order is entered. Stopping payments accrues arrears with interest and can result in enforcement actions (wage garnishment, license suspension) even if you believe a modification is warranted. Pay what you owe, file the petition, and let the court process work.

Private agreements don't protect you. If you and the other parent agree informally to pay less, that agreement is unenforceable. The state child support enforcement agency can still pursue you for the full amount of the original court order, including any amounts you paid under the informal agreement.

How to Request a Modification

1. Gather documentation: pay stubs, termination letters, medical records, new custody schedules — whatever supports the change in circumstances.
2. File a "Motion to Modify Child Support" with the court that issued the original order (typically the family court in the county where the child lives).
3. Serve the other parent according to your state's service of process rules.
4. Attend the modification hearing. Both parents present income documentation and the court recalculates support under current guidelines.
5. Once a new order is entered, update payroll withholding if support is paid through wage assignment.

Your state's Child Support Services office can assist with modification requests at little or no cost, particularly if one parent receives public assistance. Private family law attorneys can handle contested modifications.

Data Sources & References

• U.S. Department of Health & Human Services — Office of Child Support Services (OCSS): acf.hhs.gov/css
• National Conference of State Legislatures — Child Support Guidelines by State
• U.S. Census Bureau — Survey of Income and Program Participation (SIPP), Child Support data tables
• Individual state court administrative offices and child support agency guideline tables (cited in state table above)
• American Bar Association Family Law Section — Child Support Guidelines overview

How Child Support Is Calculated by State — The 5 Most Populous States (2026)

While all U.S. states follow one of three formula models — Income Shares, Percentage of Income, or Melson — the practical results vary considerably based on each state's specific guideline tables, income caps, and allowable deductions. Here's a detailed breakdown of how the five most populous states calculate child support.

Understanding the Two Core Models

Before diving into individual states, it helps to understand the two dominant models. The Income Shares model assumes that both parents share responsibility for supporting the child in proportion to their relative incomes. Both parents' gross incomes are combined, the state's schedule specifies a total support obligation for that combined income level, and each parent pays their proportional share. The higher-earning parent typically pays their share directly to the lower-earning parent as a monthly payment.

The Percentage of Income model is simpler: a fixed percentage is applied directly to the paying parent's income only, regardless of what the other parent earns. This model favors transparency and predictability but is criticized for ignoring the receiving parent's ability to contribute. Texas is the most prominent example of this model in practice.

The key practical difference: in Income Shares states, a higher-earning receiving parent reduces the paying parent's obligation. In Percentage of Income states, only the paying parent's income matters.

California — Income Shares with a Proprietary Algebraic Formula

California uses an Income Shares model, but unlike most states, it does not rely on simple lookup tables. Instead, California's guideline is expressed as an algebraic formula established by Family Code § 4055. Courts and attorneys use specialized software (most commonly Dissomaster or XSpouse) to compute the guideline amount, which incorporates both parents' net disposable incomes (after taxes, mandatory deductions, and health insurance premiums), the paying parent's percentage of custodial time, and add-ons for childcare and healthcare.

The California formula's most distinctive feature is its sensitivity to parenting time. Because the formula directly incorporates the custodial time percentage ("H" in the formula), small changes in the parenting schedule can produce significant changes in the support obligation. A parent who increases their custodial time from 20% to 35% may see their support obligation drop by $300–$600/month depending on incomes. California also has no statutory income cap — the formula theoretically applies at any income level, though courts exercise discretion at very high incomes.

California's guideline tends to produce higher support amounts than most other states for middle and upper-middle income families, reflecting the state's high cost of living and the relatively generous treatment of the receiving parent's economic position.

Texas — Percentage of Income, Applied to Net Income

Texas uses a pure Percentage of Income model under Texas Family Code § 154.125, and is one of the clearest examples of how this model works in practice. The percentages are fixed by statute and apply to the obligor (paying parent's) monthly net resources — defined as gross income minus federal and state income taxes, Social Security, Medicare, union dues, and health insurance premiums paid for the child:

• 1 child: 20% of net resources
• 2 children: 25% of net resources
• 3 children: 28% of net resources
• 4 children: 31% of net resources
• 5 or more children: 34% of net resources

Texas caps the net resources considered for guideline support at $9,200/month (adjusted periodically). For income above this cap, courts may order additional "above-guideline" support based on the child's actual needs. The Texas Attorney General's office provides an official online child support calculator at oag.texas.gov that handles the net-to-gross conversion automatically. Texas courts also consider the amount of time the child spends with each parent, but unlike California, this is a discretionary deviation factor rather than a built-in formula element.

Florida — Income Shares with Overnight-Based Adjustments

Florida follows the Income Shares model under Florida Statute § 61.30, using detailed schedule tables that specify a minimum support obligation based on both parents' combined net income and the number of children. Florida is notable for its substantial parenting time adjustment: when the paying parent exercises 20% or more of overnights (73 or more nights per year), a specific statutory formula applies that can substantially reduce the base obligation.

Florida's guidelines also mandate specific treatment of health insurance costs. The cost of the child's health insurance coverage (the child's incremental share of the premium) is added to the base obligation and divided between parents proportionally. Similarly, net childcare costs (daycare, after-school care) required for employment are added and split proportionally. Florida courts also require both parents to disclose health insurance availability — if either parent has access to employer-sponsored coverage that would cover the child, the court will typically order that parent to maintain it.

Florida's schedule tables cap at a combined monthly net income of $10,000. For income above this cap, courts have discretion and typically look at the percentage applied at the cap level plus any actual extraordinary child expenses. For most middle-income Florida families, the income shares table at a combined net income of $6,000–$9,000/month typically produces a base obligation of $1,200–$2,000/month for two children before custody adjustments.

New York — Income Shares via the Child Support Standards Act (CSSA)

New York's Child Support Standards Act (Family Court Act § 413) uses an Income Shares approach with a percentage-of-combined-income structure and an income cap. The CSSA applies fixed percentages to the combined parental income up to the statutory cap (currently $183,000/year as of 2024, adjusted biennially for inflation):

• 1 child: 17% of combined income
• 2 children: 25% of combined income
• 3 children: 29% of combined income
• 4 children: 31% of combined income
• 5 or more children: 35% of combined income (or more)

The non-custodial parent pays their proportional share of that total obligation as their basic child support payment. New York also sets a Self-Support Reserve — in 2026, approximately $21,500/year — below which the paying parent's income will not be reduced by basic child support (though a minimum order may still apply). For income above the cap, courts must make a written determination about whether to apply the CSSA percentage to additional income or use an alternative analysis based on the child's actual needs and the parents' financial resources.

New York is also notable for mandatory add-ons: childcare expenses, educational and healthcare expenses, and college education costs for children under 21 may all be ordered as add-ons to basic support, split proportionally. New York child support orders frequently run higher than many other states for high-income families precisely because the courts have broad discretion above the cap.

Illinois — Income Shares with Net Income Basis

Illinois follows the Income Shares model under 750 ILCS 5/505, revised significantly in 2017. Uniquely among major states, Illinois bases its calculation on net income (income after federal and state taxes, Social Security, Medicare, and mandatory union dues) rather than gross income. This means Illinois parents must calculate after-tax income before applying the guideline tables — a step that adds complexity but arguably reflects actual available income more accurately.

Illinois uses statutory income shares tables that specify a minimum support obligation based on combined net monthly income and number of children. Each parent is then responsible for their proportional share of that obligation based on their percentage of combined net income. The Illinois schedule also includes a parenting time adjustment: when the paying parent exercises significant parenting time (146 or more overnights per year, or 40%), a shared parenting formula applies that reduces the base obligation to reflect the direct costs each parent bears during their parenting time.

Illinois courts also add health insurance costs (the child's incremental premium share) and work-related childcare costs proportionally to the base obligation. Illinois has no hard income cap in its statute — the guideline tables extend to high income levels, and courts apply the percentage tables beyond the table maximum.

Child Support Model Comparison — Top 5 States

Quick-reference comparison for the five most populous U.S. states. Modification threshold = approximate minimum change in circumstances required to petition for modification.

Sources: CA Family Code § 4055; TX Family Code § 154.125; FL Statute § 61.30; NY Family Court Act § 413 (CSSA); 750 ILCS 5/505. Base percentages are approximate for median-income families. Updated August 2026.