How California calculates child support
California does not use a lookup table. Family Code §4055 gives an algebraic formula that uses both parents' net disposable income and the share of time each parent has the children. The same formula covers parents who never share time and parents who split time evenly, so there is no separate shared custody rule. The result is presumed correct, and a court may depart from it only on the grounds in §4057.
Net disposable income
Each parent's monthly net disposable income (§4059) is gross income minus income taxes actually owed under the parent's real filing status, Social Security and Medicare, mandatory union dues and retirement required by the job, health insurance premiums for the parent and the children the parent supports, state disability insurance premiums, and child or spousal support actually paid under court order for people who are not part of this case. Without an order, child support actually paid for the parent's own children who live elsewhere also counts, up to the guideline amount, if the parent proves the payment. Two more deductions depend on the court: job-related expenses the court allows, and hardship deductions, for example for other children living with the parent (§§4059, 4070-4073). The statute takes the actual tax liability, not the amount withheld, and does not set any tax table. The calculator therefore asks you for the net figure rather than guessing at taxes. A new spouse's income is generally not counted (§4057.5). Spousal support the parents pay each other is not income for the basic formula, and its tax effects are left out unless the parents agree otherwise (§4059(a)). It does count when child care and other add-ons are split (see below).
The formula
Child support is K [ HN - (H%)(TN) ], where HN is the higher earner's net disposable income, TN is the combined total, and H% is the share of time the higher earner has the children. K is a fraction that changes with TN and with H%. It is (1 + H%) x F when H% is 50% or less, and (2 - H%) x F when it is higher. F depends on combined income:
| Combined net disposable income | F |
|---|---|
| $0 to $2,900 | 0.165 + TN / 82,857 |
| $2,901 to $5,000 | 0.131 + TN / 42,149 |
| $5,001 to $10,000 | 0.25 |
| $10,001 to $15,000 | 0.10 + 1,499 / TN |
| Over $15,000 | 0.12 + 1,200 / TN |
The result is for one child. For two or more, it is multiplied by 1.6 for 2, 2 for 3, 2.3 for 4, 2.5 for 5, 2.625 for 6. If the formula comes out positive, the higher earner pays the lower earner. If it is negative, the lower earner pays the higher earner. H% is the approximate share of time the higher earner has primary physical responsibility for the children, and when the children have different schedules it is the average of the percentages for each child (§4055(b)(1)(D)). Overnights are only a stand-in for that share: the calculator divides the higher earner's overnights by 365, or you can enter the percentage directly in the extra fields. The statute does not specify a rounding rule.
The low-income adjustment
If the paying parent's net disposable income is less than a full-time minimum-wage worker earns in a month (40 hours a week, 52 weeks a year, at the state rate in Labor Code §1182.12), there is a rebuttable presumption of a low-income adjustment (§4055(b)(7)). At $16.90 an hour that is $2,929.33 a month in 2026, and $17.40 an hour ($3,016.00) from January 1, 2027. The statute caps the reduction at the formula amount times the gap between that threshold and the parent's income, divided by the threshold. It does not set a fixed amount, so the calculator shows the maximum reduction and a second figure: the whole monthly support with the full reduction, including child care split again on the reduced basic support, because the add-ons are shared after the basic support is set (§4061(b) and (d)). The presumption can be rebutted, so the court decides how much of the reduction to apply, if any. That lowest result is not a floor for every case: if the support after the low-income adjustment still exceeds 50% of the payer's net disposable income, the court may reduce it further, by no more than the excess (§4057(b)(5)). That is a separate finding, so the calculator only points it out.
Child care and other add-ons
Child care costs that are actually paid and are related to a parent's job, or to education or training reasonably needed for employment skills, are added to the basic amount unless they are already specifically included in the guideline calculation itself, and reasonable uninsured health costs are shared (§4062(a)). Care for other activities is not part of that mandatory add-on. The split is in proportion to net disposable income, with two adjustments: spousal support ordered between the parents is taken off the payer's income and added to the recipient's while it is paid, and the income of the parent paying basic child support is reduced by that support, while the other parent's is not increased (§4061(c)-(d)). Each parent owes a share of the child care the other one pays, whoever pays the basic support, so child care is owed even when the basic support is zero, and it can make the net transfer run the other way. The calculator includes child care; uninsured health costs are shared as they arise and are not in the monthly figure. Educational or special needs and visitation travel are discretionary add-ons the calculator does not estimate.
Where the court decides
Courts may use earning capacity when income is unknown or when a parent chooses not to work, may allow hardship deductions for the parent's other children, and may depart from the guideline under §4057 in cases such as extraordinarily high income or special needs. Spousal support in California has no formula: it depends on the factors in Family Code §4320.