Child support is one of the most frequently contested issues in any divorce or separation involving children. Every state sets its own guidelines, but all states are required by federal law to have a formula-based system — so the starting point is always a calculation, not a guess. What varies is the formula itself, the inputs that feed it, and how much judges can stray from the result.
This guide covers how the most common calculation models work, what counts as income, common reasons courts deviate, how support is enforced, and how to modify an order if circumstances change. Because state rules differ significantly, treat all examples here as illustrative. An attorney in your state can tell you exactly how local guidelines apply to your situation.
The Two Main Calculation Models
Income Shares Model (Most States)
The income shares model starts from a simple premise: children should receive the same proportion of their parents' combined income they would have received if the household had stayed intact. About 41 states use this approach.
The calculation works in steps. First, both parents' gross monthly incomes are added together. Second, that combined figure is run through a state-published schedule that assigns a basic child support obligation based on income level and number of children. Third, each parent's share of the combined income determines their share of that obligation. The noncustodial parent typically pays their share directly to the custodial parent; the custodial parent's share is presumed to be spent directly on the child.
Example: Parent A earns $5,000/month; Parent B earns $3,000/month. Combined income is $8,000. If the state schedule sets a $1,200 baseline for one child at that income level, Parent A — who earns 62.5% of combined income — would owe $750/month.
Percentage of Income Model (Fewer States)
A smaller group of states, including Texas and Wisconsin, use the percentage of income model. Here, support is simply a fixed percentage of the paying parent's net or gross income, regardless of what the receiving parent earns. It is easier to calculate but does not account for the receiving parent's ability to contribute.
Typical percentages in these states run roughly 17–25% of net income for one child, increasing incrementally for additional children — though the exact percentages vary by state and are subject to caps and floors.
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Run the Free CalculatorWhat Counts as Income
Courts cast a wide net when defining income for child support purposes. In most states, income includes virtually any regular source of money — not just wages and salary. Common income sources that factor into the calculation:
- Wages, salary, tips, and overtime
- Self-employment income (net of legitimate business expenses)
- Bonuses and commissions
- Rental income
- Investment income — dividends, capital gains, interest
- Pension and retirement distributions
- Disability and workers' compensation benefits
- Unemployment compensation
- Alimony received from a prior relationship
What generally does not count: means-tested public assistance (SNAP, Medicaid, SSI), child support received for other children, and certain adoption subsidies. Courts can also impute income — assigning earning capacity rather than actual earnings — if a parent is voluntarily underemployed or unemployed without good cause.
Sample Monthly Amounts: 1 Child
The figures below are illustrative estimates based on typical income shares schedules. Actual amounts vary significantly by state. Do not rely on this table for any legal or financial decision.
| Combined Monthly Income | Estimated Guideline Amount | Noncustodial Share (50% income split) |
|---|---|---|
| $3,000 | $450 – $520 | ~$225 – $260 |
| $5,000 | $680 – $780 | ~$340 – $390 |
| $7,500 | $920 – $1,050 | ~$460 – $525 |
| $10,000 | $1,150 – $1,300 | ~$575 – $650 |
| $15,000 | $1,500 – $1,750 | ~$750 – $875 |
| $20,000 | $1,800 – $2,100 | ~$900 – $1,050 |
Common Deviations Courts Allow
The guideline number is a starting point, not a ceiling or a floor. Courts in most states have discretion to deviate — up or down — when specific circumstances justify it. Common grounds for deviation include:
- Childcare costs: Work-related daycare or after-school care expenses are frequently added on top of the base obligation and split proportionally between parents.
- Health insurance premiums: The cost of the child's share of health insurance is typically added to the base and allocated between parents. Uninsured medical expenses are often split 50/50 or proportionally.
- Extraordinary educational expenses: Private school tuition or tutoring may be added if both parties historically maintained that standard.
- Special needs: A child with significant medical, therapeutic, or developmental needs may result in a higher-than-guideline order.
- High income: Most state schedules cap out at a certain combined income level. Above that cap, courts use discretion rather than formula.
- Substantial parenting time: In many states, a noncustodial parent with significant overnight custody (often 40% or more) may receive a reduction to account for direct costs incurred during their parenting time.
- Multiple families: Existing child support orders for other children are often deducted from income before calculating a new obligation.
States by Calculation Model
The table below reflects the model in general use as of 2026. State legislatures can and do revise their guidelines, so verify with your state's official child support enforcement agency.
| Model | States (Representative Examples) |
|---|---|
| Income Shares | California, Florida, Georgia, Illinois, Michigan, New York, Ohio, Pennsylvania, Virginia, and approximately 36 other states |
| Percentage of Income | Texas, Wisconsin, Alaska, Mississippi, Nevada (hybrid) |
| Melson Formula (hybrid) | Delaware, Hawaii, Montana |
When Does Child Support End?
Termination age is one of the sharpest variations across states. Most terminate support at age 18, but the details matter:
- Age 18: The baseline in the majority of states. Some add "or high school graduation, whichever is later" — meaning a 19-year-old still in high school may still receive support.
- Age 19: Alabama and a few others use 19 as the cutoff.
- Age 21: New York, for example, terminates support at 21. Indiana's statute similarly extends in certain circumstances.
- College: A small number of states — including Massachusetts, Connecticut, and New Jersey — permit courts to order support through undergraduate education, though this area of law is unsettled and actively litigated.
Support also ends early upon certain events in most states: the child's marriage, entry into active military service, or legal emancipation. Parents can agree in writing to extend support voluntarily beyond the statutory end date.
How Child Support Is Enforced
Federal law requires every state to maintain a child support enforcement agency, and these agencies have broad tools available when a paying parent falls behind:
- Income withholding: The most common tool. Most orders include an automatic income withholding provision that directs the employer to deduct support from wages before the paycheck is issued.
- Tax refund intercepts: State and federal tax refunds can be seized and applied to past-due support (arrears).
- License suspension: Driver's licenses, professional licenses, and hunting/fishing licenses can be suspended in most states for significant arrears.
- Credit reporting: Unpaid support above a threshold is reported to credit bureaus.
- Passport denial: Owing more than $2,500 in arrears can result in passport denial or revocation under federal law.
- Contempt of court: A judge can hold a parent in civil or criminal contempt, which can result in fines or jail time in serious cases.
Modifying Child Support
A child support order is not permanent. Either parent can request a modification when there has been a "substantial change in circumstances" — the specific threshold varies by state but commonly means a change of 15–20% or more in the guideline amount. Qualifying changes include:
- A significant increase or decrease in either parent's income
- Job loss or involuntary reduction in hours
- A material change in the child's needs (new medical condition, change in childcare costs)
- A change in the custody arrangement that affects parenting time percentages
- The paying parent becoming responsible for additional children
To modify an order, you typically file a motion with the court that issued the original order. Some states allow administrative modifications through the child support enforcement agency without going back to court. Until a court formally modifies the order, the original amount remains legally owed — paying less voluntarily does not reduce arrears.
Many states also build in automatic review triggers: orders may be reviewed every three years upon request by either parent, even without a demonstrated change in circumstances.
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Use the Free CalculatorA Note on Using This Information
Child support law is state-specific and fact-specific. The rules summarized here reflect typical guidelines across states, but your state may calculate income differently, use a different schedule, or apply different deviation standards. An attorney or your state's child support enforcement office can provide calculations based on the actual figures in your case. This page is educational only and does not constitute legal advice.