Child Support Calculator
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Income Share %
How Child Support Is Calculated
Child support is a court-ordered payment from one parent to the other to cover a child's basic living expenses after separation or divorce. According to the federal Office of Child Support Services (OCSS), the US child support program collected and distributed approximately $29 billion to families in fiscal year 2023, serving over 13 million cases. Each state sets its own guidelines using one of three models: the Income Shares Model (used by approximately 40 states), the Percentage of Income Model (about 9 states), or the Melson Formula (3 states). This calculator uses a simplified Income Shares approach to provide a general estimate.
The Income Shares Model, recommended by the National Conference of State Legislatures, is based on the principle that a child should receive the same proportion of parental income as they would if the parents lived together. Both parents' incomes are combined, a basic support obligation is determined from a schedule based on the number of children, and each parent's share is proportional to their percentage of the combined income. Additional factors include health insurance premiums, childcare costs, and extraordinary expenses. Use our salary calculator to determine gross income figures for the inputs.
The Child Support Formula
Under the Income Shares Model, child support is calculated as: Non-Custodial Parent's Obligation = Basic Support Obligation x (Non-Custodial Parent Income / Combined Income) - Overnight Adjustment. The basic support obligation is determined from state-specific schedule tables that increase with combined income and number of children. Most states apply a percentage of combined income: approximately 20% for one child, 28% for two, 33% for three, 38% for four, and 42% for five or more.
Worked example: Parent 1 earns $5,000/month gross, Parent 2 earns $3,500/month gross. Combined income = $8,500. With 2 children, the basic support obligation is approximately 28% of $8,500 = $2,380/month. Parent 1's income share is $5,000 / $8,500 = 58.8%. Parent 1's obligation = $2,380 x 0.588 = $1,400/month. If Parent 1 has the children for 52 overnights per year (14.2% of nights), most states would not apply an overnight credit because the threshold (typically 20-30%) is not met.
Key Terms You Should Know
- Income Shares Model: Calculates support based on both parents' combined income, used by ~40 states. The philosophy is that the child should receive the same share of income as if parents lived together.
- Percentage of Income Model: Applies a flat percentage of only the non-custodial parent's income (17-25% depending on number of children), used by ~9 states including Wisconsin and Texas.
- Imputed Income: When a parent is voluntarily unemployed or underemployed, courts may assign ("impute") income based on their earning capacity, education, and work history rather than actual earnings.
- Overnight Credit: A reduction in child support based on the number of overnight stays with the non-custodial parent. Most states apply this when overnights exceed 20-30% of the year (73-110 nights).
- Deviation Factors: Courts can deviate from guideline amounts for special circumstances including extraordinary medical expenses, travel costs for long-distance visitation, or educational needs of the child.
State Child Support Models Comparison
The three calculation models produce significantly different support amounts for the same family situation. The table below illustrates how each model would calculate support for a family with $8,500 combined monthly income and 2 children.
| Model | States Using | Basis | Example Amount (2 kids) | Key Feature |
|---|---|---|---|---|
| Income Shares | ~40 states | Combined income | $1,200-$1,500/mo | Both incomes considered |
| Percentage of Income | ~9 states | Non-custodial income only | $1,000-$1,250/mo | Simpler calculation |
| Melson Formula | 3 states (DE, HI, MT) | Income after self-support | $900-$1,200/mo | Ensures parent's basic needs met |
Practical Examples by Scenario
Example 1 -- Sole custody, standard income: Parent 1 earns $6,000/month, Parent 2 earns $4,000/month, 1 child, sole custody with Parent 2. Using the Income Shares Model: combined income = $10,000, basic support at 20% = $2,000, Parent 1's share = 60% = $1,200/month. Annual support = $14,400.
Example 2 -- Joint custody with overnight credit: Same incomes, 2 children, but Parent 1 has 130 overnights (35.6%). Basic support = $2,800, Parent 1's share = $1,680. With 35.6% overnights exceeding the 20% threshold, the overnight credit reduces the obligation by approximately $520, resulting in adjusted support of about $1,160/month. Use our budget calculator to plan around these payments.
Example 3 -- High-income scenario: Parent 1 earns $15,000/month, Parent 2 earns $5,000/month, 3 children. Combined income = $20,000, basic support at 33% = $6,600, Parent 1's share = 75% = $4,950/month. Many states cap the combined income used in calculations (often at $20,000-$30,000/month), so support for very high earners may not scale linearly.
Enforcement and Modification
- Automatic wage garnishment: Under the Consumer Credit Protection Act, up to 50% of disposable income can be garnished for current support (60% if no other dependents), increasing by 5% for arrears over 12 weeks.
- Tax refund interception: The federal Tax Refund Offset Program intercepts refunds for parents who owe $150+ in arrears for cases receiving government assistance, or $500+ for non-assistance cases.
- Passport denial: The US State Department will deny or revoke passports for parents with arrears exceeding $2,500, per 42 USC 654(31).
- Modification process: Either parent can petition for modification when circumstances change. Most states allow review every 2-3 years or when income changes by 15-25%. Use our US income tax calculator to estimate net income impacts.
- Interstate enforcement: The Uniform Interstate Family Support Act (UIFSA) allows enforcement across state lines. Only one state can have jurisdiction over a support order at a time.
Frequently Asked Questions
How long does child support last in the US?
In most states, child support continues until the child turns 18 or graduates high school (whichever is later). Some states like New York extend support to age 21. States including Indiana, Iowa, and Utah can order parents to contribute to college costs. Children with special needs or disabilities may receive support indefinitely if they cannot become self-supporting. According to the Office of Child Support Services, approximately $29 billion in child support was distributed to families in fiscal year 2023.
Can child support be modified after the initial order?
Yes, either parent can request a modification if there is a substantial change in circumstances such as job loss, a 15-25% change in income (threshold varies by state), change in custody arrangement, or change in the child's needs. Most states allow periodic review every 2-3 years even without a change in circumstances. Courts must approve all modifications -- parents cannot unilaterally change support amounts.
What happens if child support is not paid?
The federal OCSS reports approximately $113 billion in child support arrears nationwide. Enforcement consequences include automatic wage garnishment (up to 50-65% of disposable income), federal and state tax refund interception, driver's license and passport suspension (for arrears over $2,500), property liens, credit reporting, contempt of court charges, and potentially jail time. The Deadbeat Parents Punishment Act makes willful non-payment across state lines a federal crime.
What is the difference between Income Shares and Percentage of Income models?
The Income Shares Model (used by ~40 states) calculates support based on both parents' combined income and allocates each parent's share proportionally. The Percentage of Income Model (~9 states including Wisconsin and Texas) applies a fixed percentage of only the non-custodial parent's income: typically 17% for one child, 25% for two. The Melson Formula (Delaware, Hawaii, Montana) ensures each parent retains a self-support reserve before calculating the obligation.
Does child support cover college expenses?
This varies by state. States including Indiana, Iowa, Massachusetts, New York, and Utah can order parents to contribute to college costs. Most states end support at age 18 or high school graduation. Courts typically consider the child's academic ability, parents' financial capacity, and institutional cost. Use our college cost calculator to estimate education expenses.
How does joint custody affect child support payments?
Joint or shared custody typically reduces child support through an overnight credit. Most states apply a reduction when the non-custodial parent has the child more than 20-30% of overnights (73-110 nights per year). For example, if calculated support is $1,200/month and the non-custodial parent has 40% of overnights, the adjusted amount might be $700-$900/month. The exact formula varies significantly by state.