Child support isn't haggled from scratch; it comes out of a formula your state wrote down. 41 states use the income-shares model: estimate what the parents would spend on the kids together, then split it by income. Texas charges the paying parent a flat 20% to 40% of net resources. New York applies 17% to 35% of combined income up to $193,000. The models differ, but every one of them starts with income.
There are three, and knowing yours tells you most of what the number will look like.
Income shares, used by 41 states, works from a simple idea: figure out what the parents would spend on the children if they lived under one roof, then split that obligation in proportion to income. New York's version, the Child Support Standards Act, runs 17% of combined parental income for one child, 25% for two, 29% for three, 31% for four, and at least 35% for five or more, applied up to a combined-income cap of $193,000 (effective March 1, 2026, up from $183,000; it adjusts every two years, next in March 2028).
A worked example makes it concrete. Two parents with a combined income of $150,000 and 2 children owe 25%, a $37,500 annual obligation. The noncustodial parent earns $90,000, which is 60% of the combined income, so they pay 60% of the obligation: $22,500 a year, about $1,875 a month.
Percentage-of-income states skip the combining step and take a flat cut of only the paying parent's income. Texas is the flagship. Family Code §154.125 sets 20% of monthly net resources for one child, 25% for two, 30% for three, 35% for four, and 40% for five or more. A paying parent netting $6,000 a month with two kids owes $1,500 a month, no lookup table required.
The Melson formula, used in Delaware, Hawaii, and Montana, is a stricter, multi-step cousin of income shares. If you live in one of those three states, lean on the official worksheet early; the shorthand math in this guide won't get you close.
Almost everything: wages, salary, overtime, bonuses, commissions, and self-employment profits, and many states pull in rental and investment income too. The bigger trap is gross versus net. Texas runs on "net resources," California on net disposable income, and Pennsylvania and Illinois both build their tables from net figures, while other states start from gross. The state defines its own deductions either way, so your pay stub is a starting point, not the answer. It helps to know your real take-home before you estimate anything: a salary calculator converts your wage between hourly, monthly, and annual, and an income tax calculator shows what's actually left after taxes.
In most income-shares states, time matters once it crosses a threshold. Illinois switches to a shared-parenting calculation at 146 or more overnights a year. Michigan's formula has a built-in parenting-time offset, so every extra overnight nudges the payment down. Florida changes the formula when time-sharing is substantial. New Jersey uses entirely separate worksheets for sole and shared parenting.
California goes furthest: parenting time sits inside the algebra itself. The §4055 formula is CS = K × (HN − H% × TN), where H% is the higher earner's share of parenting time. More time with the higher earner directly shrinks the payment, and if the higher earner has most of the time, the result can go negative, meaning support flows to them instead. One thing no state does: treat 50/50 time as an automatic zero. If incomes differ, a payment usually survives equal schedules.
The guideline figure is the base, not the invoice. Health-insurance premiums for the kids and work-related childcare typically get split between the parents pro-rata, on top of the base number. So a parent with a 60% income share generally covers 60% of the premium and 60% of daycare, in addition to the guideline amount. When people are shocked by the total on the final order, the add-ons are usually why.
Income-shares, Texas, New York, and California modes, with the income caps applied automatically.
Child Support Calculator →Courts saw the quit-your-job trick coming decades ago. If a parent is voluntarily unemployed or underemployed, the judge can impute income: calculate support as if that parent earned what they reasonably could, based on their history and qualifications, rather than the number on this year's return. This cuts both ways. A paying parent can't shrink the obligation by taking a token job, and a receiving parent who could work may have income attributed to them in an income-shares split. Genuine job loss is different, and that's what modification is for.
| State | Model | The short version |
|---|---|---|
| Texas | Percentage of net resources | 20% for 1 child up to 40% for 5+; net resources capped at $11,700/mo for orders on or after September 1, 2025; guideline max for 1 child is $2,340/mo |
| New York | Income shares (CSSA) | 17% to at least 35% of combined income up to $193,000, split pro-rata; judges have discretion above the cap |
| California | Statewide formula (§4055) | CS = K × (HN − H% × TN), run in court-certified software; 2 children ×1.6, up to ×2.5 for 5 |
The Texas cap deserves a note: $11,700 is the first adjustment since 2019, up from $9,200, and it means very high earners hit a ceiling. A parent netting $15,000 a month pays the same guideline amount for one child as a parent netting exactly $11,700: 20% of the cap, or $2,340.
And a California example, because the formula looks scarier than it is. Say the higher earner nets $8,000 a month, the parents' combined net is $11,000, and the higher earner has the kids 20% of the time. The formula produces roughly $1,341 a month for one child. Two children apply a 1.6 multiplier, landing near $2,146. Every California courtroom runs this through certified software, so the judge's number and the formula's number match by construction.
In most states, support runs to age 18 or high-school graduation. Several states go later, and New York goes to 21. The order doesn't always stop by itself, and when it covers several kids, one child aging out usually means a recalculation, not a do-it-yourself reduction.
Changing an order means going back to court and showing a material change in circumstances: a job loss, a big raise, a new custody schedule. Two rules matter more than any other. First, the existing order keeps accruing until a judge signs a new one, no matter how reasonable your informal arrangement feels. Second, arrears don't vanish. Past-due support survives more or less everything, so the parent whose income drops should file immediately rather than fall behind and hope for sympathy later.
This calculator is for education only and is not legal advice. Courts can and do deviate from guideline numbers. Use your state's official worksheet or calculator for anything you'll file.
It depends on the state. Texas applies its percentages to net resources, California's formula runs on net disposable income, and states like Pennsylvania and Illinois build their income-shares tables from net figures. Others start from gross. Every state defines its own deductions, and they rarely match your pay stub line for line, so use the definitions on your state's official worksheet.
In the 41 income-shares states, yes: both incomes are combined to set the obligation, then each parent covers their proportional share. In percentage-of-income states like Texas, the base formula looks only at the paying parent's net resources. The other parent's income can still matter at the edges, since judges can deviate from the guideline when circumstances call for it.
Yes. The guideline number is a presumption, not a ceiling or a floor. Judges deviate for things the formula handles poorly, and New York makes the discretion explicit: above the $193,000 combined-income cap, the court decides how much of the extra income to count. Add-ons like health insurance and childcare also go on top of the base figure.
Only if incomes are roughly equal. With a real income gap, most states still order the higher earner to pay something so the children live comparably in both homes. Some formulas account for time directly: California's H% variable, Illinois's shared-parenting calculation at 146 or more overnights, and Michigan's parenting-time offset all shrink the number as overnights increase, without automatically zeroing it.