How the income-shares formula works
The income-shares model assumes a child should receive the same proportion of parental income they would have received if the parents still lived together. Three steps:
- Combine both parents' monthly income. Most states use gross income and then subtract a short list of standardized deductions (mandatory retirement, union dues, existing child support for other children).
- Look up a base support obligation in the state schedule. As a rough rule, combined support runs about 17% of combined income for one child, 25% for two, 29% for three, and 31%+ for four.
- Prorate the obligation by each parent's income share and adjust for custody time. The non-custodial parent pays their share of the base.
2026 state schedule examples
At a combined gross income of $120,000/year and two children, base guideline support is roughly:
- California: ~$1,850/month combined
- Florida: ~$1,920/month combined
- New York: $2,000/month combined (17% for 1 child, 25% for 2, 29% for 3)
- Texas (percentage model): 20% of obligor net for 1, 25% for 2
- Pennsylvania: ~$1,780/month combined
- Illinois: ~$1,810/month combined
Worked example with 60/40 custody
Mom earns $7,500/month gross, dad earns $4,500/month gross. Two children. Mom has the kids 60% of the time.
- Combined income: $12,000/month
- Mom's share: 62.5%, dad's share: 37.5%
- Base support at 25% for two kids: $3,000/month
- Mom's obligation when kids are with dad (40% of time): 62.5% × $3,000 × 40% = $750
- Dad's obligation when kids are with mom (60% of time): 37.5% × $3,000 × 60% = $675
- Net: Mom pays dad $75/month
Counterintuitive, right? Mom earns more, has them more, and still owes a small amount because of the equalization math. That's the income-shares model in action.
Add-ons that change the number
Base support is rarely the final bill. Expect separate line items for:
- Health insurance premium for the child — the paying parent gets a credit, the other parent reimburses their prorated share
- Uninsured medical expenses (dental, orthodontia, therapy, copays) — typically split by income share after a $250–$500 annual threshold
- Work-related childcare — prorated by income share
- Extracurricular activities — some states include (Virginia, Maryland), others leave it to the parents to agree on
- Private school tuition — allocated case by case, usually if the child already attended before separation
- College expenses — only a few states (IL, MA, NJ, NY, IN) can order college contribution by statute
When the guideline number gets ignored
Judges deviate from the calculated number when:
- High-income cases above the schedule cap: Most states cap the schedule at $20,000–$40,000 combined monthly income. Above the cap, the court uses discretion and often caps total support at a lifestyle-driven amount.
- Shared custody below the statutory split: In many states, 30%+ overnights with the non-custodial parent triggers a shared-parenting discount of 10–30%.
- Imputed income: A parent voluntarily unemployed or underemployed can be assigned their earning capacity rather than actual earnings.
- Second family: Existing court-ordered support for other children is deducted before the schedule runs, but a new live-in partner's income usually is not.
- Special-needs child: Medical, therapy, and equipment costs often push support well above the schedule.
Enforcement reality
Child support is the most aggressively enforced debt in the US. Federal Title IV-D programs in every state will garnish wages, intercept tax refunds, suspend driver's and professional licenses, deny passports for arrears over $2,500, and ultimately jail for contempt. In 2024 the federal Office of Child Support Enforcement collected about $33 billion on behalf of 13 million children. A support order is not a suggestion.
If your income drops, file a motion to modify immediately. Arrears accrue until a judge signs a modification — you cannot retroactively reduce support for the months before you filed.
Getting to a fair number without fighting
The cheapest path to a child support number is for both parents to run the state's official worksheet together. All 50 states publish free online calculators (search "[state] child support calculator" — use the .gov link). Agree on the income inputs, plug them in, take that number to a mediator or judge for sign-off. Fighting over support costs $4,000–$15,000 in attorney time, and judges rarely deviate far from the guideline.
If you need help planning legal budgets overall, see the divorce cost calculator and attorney fee calculator. Low-income parents should run the legal aid eligibility quiz — every state has a legal aid office that handles support establishment and modification at no cost.