Every state has a guideline, and it is presumed correct
Federal law requires each state to set guidelines for child support amounts, by statute or by court or agency rule, and to review them at least once every four years (42 U.S.C. §667(a)). The amount the guideline produces is a rebuttable presumption: a judge or agency may order something else only with a written finding, or a specific finding on the record, that the guideline amount would be unjust or inappropriate in that case (§667(b)(2)). Federal rules add that the finding must state what the guideline amount would have been and why the order differs (45 C.F.R. §302.56(g)).
Within those limits each state writes its own formula. Almost all of them fall into one of three families: a percentage of income, income shares, or an algebraic formula written into the statute. The model decides whose income counts, whether taxes come out first, and how much the time each parent spends with the children matters.
The percentage model
A percentage state applies a fixed share of income for the number of children. In its purest form only the paying parent's income is used.
Texas works this way. The guideline starts from the paying parent's monthly net resources: resources less the deductions listed in Tex. Fam. Code §154.062(d), which are Social Security taxes, federal income tax computed for a single person with one personal exemption and the standard deduction, state income tax, union dues, the cost of the child's court-ordered health or dental insurance or cash medical support, and, for a parent who does not pay Social Security taxes, required retirement plan contributions. For net resources from $1,000 a month up to the cap, the schedule applies 20% for one child, 25% for two, and so on up to 40% for five (§154.125(b)). Below $1,000 a month a lower schedule applies, from 15% for one child to 35% for five (§154.125(c)). Above the cap, $11,700 a month since September 1, 2025, the percentages apply only to that first part, and the court may add more depending on the parents' income and the child's proven needs (§154.126). For a parent who also has a duty to support children in another household, the amount is adjusted for them, by a credit computed under §154.128 or by the alternative table in §154.129. The other parent's income and the parenting schedule are not part of the formula; they matter only if a court considers departing from it.
New York also uses fixed percentages, but applies them to the combined income of both parents: 17% for one child, 25%, 29% and 31% for two to four, and at least 35% for five or more (Family Court Act §413(1)(b)(3)). The result is split by each parent's share of income, and the non-custodial parent's share is the starting amount. Low-income rules can replace it: if paying it would leave that parent below the federal poverty guideline for one person, the basic obligation is $25 a month, and if it would leave the parent below the self-support reserve, it is $50 a month or the income above the reserve, whichever is greater (§413(1)(d)). The court can also order a different amount on the factors in §413(1)(f). The percentage applies to combined income up to $193,000 a year; above that the court decides. Because both incomes count and the result is prorated, the arithmetic ends up close to income shares, even though the statute is written as a percentage.
The income shares model
Income shares is the most common approach. The idea is that a child should receive the share of income the parents would have spent if they lived together. A schedule set by the state gives a basic obligation for the parents' combined income and the number of children. Each parent owes a share of that amount equal to his or her share of combined income. The parent who does not have the children most of the time pays that share to the other parent, who is presumed to spend the rest directly.
The schedule is only the starting point. Work-related child care and the children's health insurance are usually added and split in the same proportion, and most income shares states lower the amount once the paying parent has the children for enough overnights. New Jersey's guidelines say it plainly: the schedule reflects spending in an intact family, where the children live in one household, so it is fully appropriate only when the children live with one parent all of the time.
Of the states we cover, New Jersey, Colorado, Pennsylvania, Virginia, Arizona and Florida use income shares. They differ in whether they start from gross or net income, in the size and age of their schedules, in low-income protections, and in how they treat shared parenting time.
A formula in the statute
California has no lookup table. Family Code §4055 sets child support with the formula K [ HN - (H%)(TN) ]. HN is the higher earner's monthly net disposable income, TN is the combined net disposable income of both parents, and H% is the share of time the higher earner has primary physical responsibility for the children. K is a fraction that depends on combined income and on H%. The result is for one child and is multiplied for more children (1.6 for two, 2 for three). Because the high earner's approximate share of primary physical responsibility for the children is part of the formula itself, there is no separate shared custody rule.
Which model each state uses
The table shows the model, the income each guideline starts from, and the date the schedule or rule now used by our calculator took effect.
| State | Model | Income used | In effect since |
|---|---|---|---|
| Texas | Percentage of income | Net resources of the paying parent only | September 1, 2025 |
| New York | Percentage of combined income | Gross income less Social Security, Medicare and a few listed items | March 1, 2026 |
| California | Formula in the statute | Net disposable income of both parents | September 1, 2024 |
| New Jersey | Income shares | Net income of both parents | June 1, 2026 |
| Colorado | Income shares | Gross income of both parents | March 1, 2026 |
| Pennsylvania | Income shares | Net income of both parents | January 1, 2026 |
| Virginia | Income shares | Gross income of both parents | July 1, 2025 |
| Arizona | Income shares | Gross income of both parents, before any deductions | January 1, 2022 |
| Florida | Income shares | Net income of both parents | January 1, 2011 |
Some of these dates mark a schedule, others the rule that changed most recently: in Texas it is the higher cap on net resources, and in New Jersey the annual update of the guideline text (its schedule of amounts dates from September 1, 2025). Florida's schedule has not changed since January 1, 2011.
Gross or net income
A net income state starts from income after the deductions its own support rules allow. That figure may differ from take-home pay: California, for example, deducts the income taxes actually payable, not necessarily what is withheld from each paycheck (Fam. Code §4059(a)), and Florida lists its own allowable deductions (Fla. Stat. §61.30(3)). A gross income state starts from pay before taxes; the schedule itself is built to account for typical taxes. Neither is more generous by nature. What matters is that the right number goes in: a net figure entered into a gross income formula, or the reverse, gives a wrong result. Every calculator on this site says which one it needs next to the income box.
One family, nine calculators
To show how much the model matters, here is the same family run through each calculator: Parent A has $6,000 a month and Parent B $4,000, they have two children, and the children live with Parent B with no overnights at Parent A's home. This is an illustration only, not an estimate for any real case. In each state the two figures are entered as that state's own income measure, so in a net income state they describe a family that earns more before taxes than the same figures do in a gross income state. The amounts are therefore not a ranking of states.
| State | $6,000 and $4,000 entered as | Parent A pays a month |
|---|---|---|
| Texas | gross pay (the calculator takes out taxes) | $1,239.21 |
| New York | gross income | $1,385.25 |
| California | net disposable income | $2,400.00 |
| New Jersey | net income | $1,337.30 |
| Colorado | gross income | $1,200.60 |
| Pennsylvania | net income | $1,471.00 |
| Virginia | gross income | $1,094.40 |
| Arizona | gross income | $1,133.00 |
| Florida | net income | $1,336.80 |
Only the basic amount is shown, with no child care, health insurance or other add-ons, and with every other input at the calculator's default. Texas uses only Parent A's income. Open any state's calculator to see each step of its result.
When the numbers change
Some of the figures behind these formulas are updated on a regular cycle. Texas law requires new tax charts every year for computing net income (Tex. Fam. Code §154.061(b)) and adjusts its cap on net resources for inflation every six years (Tex. Fam. Code §154.125(a-1)). New York recomputes its combined income cap every two years on March 1, the next time on March 1, 2028, and updates its self-support reserve every March 1. California's low-income adjustment follows the state minimum wage, which rises on January 1, 2027. Other changes come from a separate decision to revise the guidelines and have no fixed date. New Jersey has amended its guideline text every year, with recent changes taking effect on June 1. In Arizona a revised draft guideline would apply to orders entered after January 1, 2027 if it is adopted (the latest draft is dated October 21, 2026); our calculator uses the guidelines in effect since January 1, 2022.
A new schedule does not change an existing order by itself. To get a new amount, a parent usually has to ask for a review or a modification under the state's own rules.