How Child Support Is Calculated in the United States
Child support is one of the most consequential financial obligations arising from a separation or divorce involving children. Yet for most parents, the formula used to calculate it remains a mystery. Judges announce numbers in courtrooms without always explaining the math. Attorneys quote ranges without walking clients through the logic.
This guide breaks down exactly how child support is calculated, including the two primary models used across all 50 states, the factors that affect the final number, and what you can expect when you go before a judge.
Bottom line: Every state in the U.S. uses one of two basic models — the Income Shares Model or the Percentage of Income Model. Understanding which model your state uses is the single most important first step.
The Two Main Child Support Models
1. Income Shares Model (Used by ~40 States)
The income shares model is based on the principle that a child should receive the same proportion of parental income they would have received if the family had stayed together.
How it works:
- Both parents' gross monthly incomes are combined.
- A state-published schedule determines the total child support obligation based on that combined income and the number of children.
- Each parent's share of the combined income determines their proportional share of the obligation.
- The paying parent (typically the non-custodial parent) pays their proportional share to the receiving parent.
Example:
- Paying parent earns $5,000/month
- Receiving parent earns $3,000/month
- Combined income: $8,000/month
- State schedule for 2 children at $8,000: $1,800/month
- Paying parent's income share: $5,000 / $8,000 = 62.5%
- Paying parent's obligation: $1,800 × 62.5% = $1,125/month
States using the income shares model include: California, Florida, New York, Ohio, Michigan, New Jersey, Virginia, and many others.
2. Percentage of Income Model (Used by ~14 States)
The percentage of income model is simpler. It calculates child support as a fixed percentage of the paying parent's gross income, regardless of what the receiving parent earns.
How it works:
- Determine the paying parent's gross monthly income.
- Apply the state's percentage rate based on the number of children.
- That number is the base child support obligation.
Common percentage rates:
- 1 child: 17%
- 2 children: 25%
- 3 children: 29%
- 4 children: 31%
- 5 or more children: 33-35%
Example:
- Paying parent earns $5,000/month
- 2 children → 25%
- Monthly child support: $5,000 × 25% = $1,250/month
States using the percentage of income model include: Texas, Illinois, Wisconsin, Georgia, Minnesota, Mississippi, and others.
What Gets Added On Top of the Base Amount
Whether your state uses income shares or percentage of income, courts typically add additional expenses on top of the base obligation:
Childcare Costs
Work-related childcare expenses — daycare, before/after-school care — are typically added to the base support amount. In income shares states, these are usually split proportionally. In percentage states, courts have discretion.
Health Insurance Premiums
The cost of health insurance premiums for the children (the children's portion only) is added to the base amount. Courts typically require one parent to maintain coverage and reimburse the other parent accordingly.
Extraordinary Expenses
These include:
- Uninsured medical and dental costs
- Special education or tutoring expenses
- Extracurricular activity fees
- Transportation costs for visitation
Courts use discretion on extraordinary expenses. They're typically split based on each parent's proportional income.
Gross Income vs. Net Income
Most states base child support on gross income (before taxes). Some states use net income (after taxes and mandatory deductions). Knowing which your state uses matters significantly.
Gross income typically includes:
- Salary or wages
- Self-employment income
- Rental income
- Bonuses, commissions, overtime
- Social Security benefits
- Pension or retirement income
- Workers' compensation benefits
Income that may be excluded or treated differently:
- Public assistance (SNAP, Medicaid)
- SSI disability benefits
- New spouse's income (in most states)
- Child support received for other children
How Custody Affects Child Support
Custody arrangements directly impact the child support calculation:
Primary Custody (one parent has 80%+ of parenting time): The non-custodial parent typically pays the full calculated amount. The formula assumes the custodial parent is already spending their share directly on the child's day-to-day needs.
Shared Parenting (40-60% split): When parenting time is more evenly divided, most states reduce the child support obligation — often by 20-35%. The logic: if you have the kids 40% of the time, you're already spending money on them directly, so the transfer payment should be lower.
Split Custody (children split between households): When some children live primarily with one parent and others with the other parent, courts often calculate separate obligations for each parent and then offset them, with one net payment.
Deviations from the Guidelines
Child support guidelines produce a presumptive amount — a starting point. Courts can deviate upward or downward based on:
- Extraordinarily high or low income of either parent
- Significant travel costs for visitation
- A child's special medical or educational needs
- One parent paying for private school
- Existing support obligations for other children
- A child with significant assets of their own
To deviate, the requesting parent must show the guideline amount is unjust or inappropriate. Courts must document the reason for any deviation in their order.
Using Our Child Support Calculator
Our calculator on the American Child Support Calculator homepage lets you enter your state, custody arrangement, both parents' incomes, and supplemental expenses to get an educational estimate.
Remember: the calculator provides a simplified model for educational purposes. Your actual amount depends on your state's specific current guidelines, judicial discretion, and the complete facts of your case.
Frequently Asked Questions
Q: Is child support based on gross or net income? A: Most states use gross income. A few states, including Illinois and Massachusetts, use net income after mandatory deductions. Check your state's specific guidelines.
Q: Does my new partner's income affect child support? A: Generally no. Most states do not count a new spouse's or partner's income when calculating child support. However, some states may consider it in limited circumstances.
Q: Can child support be negotiated between parents? A: Yes, parents can agree to a different amount outside of court, but a judge must approve the agreement. Courts typically will not approve amounts significantly below guideline amounts unless there's good justification.
Q: When does child support end? A: In most states, child support ends when a child turns 18 or graduates high school (whichever is later), though some states extend it to age 21. Support may end earlier if a child is emancipated.
This article is for educational purposes only. Child support laws vary by state and are subject to change. This is not legal advice. Consult a licensed family law attorney in your state for guidance specific to your situation. Find a family law attorney →