What is this calculator for?
You're going through a separation, you have two kids, and the next step is figuring out what child support looks like before you sit down with a lawyer or mediator. The child support calculator uses the Income Shares model — the formula used by 41 US states — to give you a baseline number that approximates what most state courts would order. It's not a substitute for legal advice or a court order, but it tells you the range you should expect so you can plan financially and negotiate intelligently.
Child support in the US is governed state-by-state, with three primary formulas: Income Shares (41 states + DC), Percentage of Obligor Income (6 states), and Melson formula (3 states: DE, HI, MT). The Income Shares model is dominant — it combines both parents' incomes, estimates what the family would spend on the children if they were intact, and divides that obligation proportionally by income. Higher-earning parent pays more; lower-earning parent pays less. Custody arrangements (sole, shared, 50/50) further adjust the calculation.
This calculator uses Income Shares as the default and lets you select your state for state-specific adjustments. The output is a baseline estimate — your actual court order will incorporate factors the calculator can't (specific custody schedule, health insurance who's paying, extracurricular and educational costs, tax filing status post-divorce, special needs of the child, etc.).
How to use this calculator
Enter both parents' monthly gross income. Use gross (pre-tax) wage income plus any reliable monthly income from rental properties, business, or alimony received. Don't include one-time gifts, irregular bonus income, or other variable income that wouldn't sustain.
Enter number of children involved in the support obligation. The support tables increase per child but not linearly — two kids cost less than 2× the single-child obligation, three kids less than 1.5× the two-child obligation, reflecting shared housing and economies of scale.
Indicate custody arrangement: sole custody (one parent has primary residence, other has visitation), joint custody but not equal time (e.g., 70/30 split), shared 50/50 custody. Pure 50/50 custody often reduces the higher-earning parent's obligation significantly — the formula accounts for the higher-earner already providing housing, food, and care during their custody time.
Optionally enter additional costs typically allocated proportionally: health insurance premium for the children, work-related childcare costs (daycare, after-school, summer camp during working parents' shifts), extraordinary medical or educational expenses. These add to the basic obligation, with each parent contributing proportionally to income share.
Select your state. The calculator applies state-specific tables and adjustments. State variations are significant — same incomes and kids might produce $1,200/month obligation in one state and $1,800 in another.
Understanding your results
The calculator returns an estimated monthly support obligation from the higher-earning parent to the lower-earning parent (in typical Income Shares jurisdictions), with breakdown showing the basic obligation, additional cost allocations, and final amount.
How to read it. Sample: Parent A earns $7,500/month gross, Parent B earns $4,500/month, two kids, joint custody with Parent B having primary residence (70/30 time split). Combined income $12,000. State table for combined income, two kids: ~$1,800/month basic obligation. Parent A's share: 62.5% × $1,800 = $1,125. Parent B's share: 37.5% × $1,800 = $675. Since Parent B has primary custody, Parent A pays their $1,125 share to Parent B as child support. Plus proportional share of health insurance, daycare, etc.
The 50/50 custody adjustment. Same parents but pure 50/50 custody. Parent A's basic obligation is still $1,125 their proportional share, but Parent B already 'pays' their share by housing and caring for the kids 50% of the time. The court typically applies an offset: Parent A pays the difference between their share and Parent B's share = ($1,125 − $675) = $450/month. Compared to the $1,125 in primary-custody scenario, 50/50 custody reduces the high-earner's transfer by $675/month. This is why custody arrangements have substantial financial implications beyond the parenting questions.
What the calculator can't capture. (1) Tax filing changes — who claims the children as dependents affects the higher-earner's tax bill (CTC, EITC, head of household status). (2) Spousal support (alimony) — separate from child support but often negotiated together. (3) Specific extracurricular costs (private school tuition, club sports, music lessons, college expenses) — handled outside the basic formula. (4) Special needs and medical complexity — substantially increase support obligations. (5) Income variability — the calculator uses fixed income, but seasonal or commission-based incomes get averaged differently by different courts. Treat the calculator's number as a starting point; expect 10-30% variation from the actual court order.
The duration. Child support typically continues until age 18 (the federal default) or age 19/end of high school in some states. Some states extend through age 21 if the child is in college; others (Massachusetts, New Jersey) can extend to age 23. Specific orders vary based on the child's status (still in school, special needs, etc.). College tuition is sometimes separately ordered or negotiated; it's not always covered by basic child support.
A worked example
James and Aisha are separating after 12 years of marriage. Two children, ages 7 and 10. James earns $9,200/month gross as a project manager; Aisha earns $5,100/month as a teacher. They live in Pennsylvania. The kids will primarily reside with Aisha (typical 70/30 schedule). James pays $480/month for the kids' portion of family health insurance.
PA Income Shares table: combined monthly income $14,300, two children = basic monthly obligation about $2,360. James's share: $9,200 ÷ $14,300 = 64.3%. Aisha's share: 35.7%. James's basic obligation: $2,360 × 0.643 = $1,517. Plus James continues paying health insurance ($480 his cost), so Aisha owes James 35.7% × $480 = $171 (typically netted out). Daycare during her work hours: $850/month, allocated 64.3% / 35.7% = James $547 / Aisha $303. Aisha pays daycare to provider; James reimburses her his share monthly.
Net monthly transfer from James to Aisha: $1,517 + $547 daycare − $171 health insurance offset = $1,893/month. Plus James continues paying the $480 health insurance directly.
50/50 custody alternative scenario: same incomes, true 50/50 schedule. James's basic obligation $1,517; Aisha's $843. The court applies offset: James pays $1,517 − $843 = $674/month. Plus health insurance + daycare allocations. Net transfer: ~$850-1,000/month. Substantially less than the 70/30 scenario, reflecting the equal time James spends as primary caregiver.
Tax considerations: James will likely claim the older child as a dependent; Aisha the younger. Each gets head-of-household filing status (large benefit) for the half-year their respective claimed child lives primarily with them. This is a separate calculation from child support but significantly affects each parent's effective income. The decisions about custody time, dependent claims, and support amount are typically negotiated together with the help of mediators or attorneys.
Modification: 4 years later, James loses his job and takes a new role at $6,800/month — a 26% income decrease. He can petition the court for modification. New combined income $11,900; new obligation roughly $1,950 basic; James's new proportional share 57% = $1,112. Substantial reduction from the original $1,517. The petition process takes 2-4 months and requires documenting income changes; until court orders modification, the original obligation continues. Many parents fail to petition when income drops, accumulating arrears that compound the financial problem.
State-by-state variations
Income Shares states (41 + DC): use a combined-income table multiplied by basic-needs estimates. Most states have publicly-available tables on their judiciary websites. Typical for two kids at $10K combined monthly income: $1,500-2,000 basic obligation depending on state.
Percentage of Obligor Income states (6): Illinois, Mississippi, Nevada, Texas, Wisconsin, Arkansas. Formula: percentage of NON-CUSTODIAL parent's income, regardless of custodial parent's income. Typical: 20% for one child, 28% for two, 32% for three, 40% for four+. Texas: 20%/25%/30%/35%/40%/45% for 1/2/3/4/5/6+ kids. Generally produces higher orders than Income Shares for high-earning non-custodial parents.
Melson formula (3 states): Delaware, Hawaii, Montana. Hybrid Income Shares + standard-of-living adjustment for high-income earners — preserves more income for both parents than basic Income Shares.
State-specific quirks: California uses Income Shares but with its own algorithm (DissoMaster software). New York has a percentage-based cap for high incomes that effectively functions like Percentage of Obligor for very high earners. Florida uses Income Shares but has aggressive imputation of income for under-employed parents. Many states deviate when one parent is incarcerated, in long-term unemployment, or has documented medical inability to work.
Modification thresholds: most states require a "material change in circumstances" before modifying — typically 10-15% income change for either parent, change in custody arrangement, significant health change of child, or remarriage of one parent. Routine annual adjustments are not common; modifications require formal court petition.
Interstate enforcement: Uniform Interstate Family Support Act (UIFSA) means a child support order from one state is enforceable in any other state. Parent who moves out of state to avoid payment doesn't escape — the new state's enforcement can pursue wage garnishment, license suspensions, tax intercepts, even contempt of court charges leading to jail time. Federal Office of Child Support Enforcement coordinates interstate cases.
Related resources
For broader household financial planning that interacts with separation, see Income Tax Calculator (filing status changes), Paycheck Calculator (wage garnishment effects), and Net Worth Calculator (asset division context). For other family-related federal programs, the EITC & CTC Calculator (children's tax credits affected by custody) and Medicaid Eligibility. The federal Office of Child Support Enforcement provides state-by-state resources and the federal enforcement framework; state-specific calculators are typically published on each state's judiciary or department of social services website.