California Child Support: How the Guideline Formula Works, With a Worked Example

California does not set child support at a flat percentage of the paying parent's income. It uses a formula written into the Family Code, and the formula looks at both parents' incomes and at how much time each spends with the children. The result is presumed correct. A judge can depart from it only for reasons the statute lists.

Most people never do the math by hand; courts and lawyers use certified software, and the state offers a free calculator. But knowing what goes into the formula tells you which facts matter, and which arguments are worth making.

The formula

Family Code § 4055(a):

(a) The statewide uniform guideline for determining child support orders is as follows: CS = K[HN - (H%)(TN)].

Each letter is defined in § 4055(b)(1):

"Net disposable income" is income after taxes and certain mandatory deductions, such as health insurance premiums and required retirement contributions; § 4059 lists them. "Income" is broad. Under § 4058, it means gross income "from whatever source derived," and a court can use a parent's earning capacity instead of actual earnings in the circumstances that section allows.

If the result is positive, the higher earner pays the lower earner. If it is negative, the lower earner pays (§ 4055(b)(5)). That happens when the lower earner has the children much less of the time.

Finding K

K depends on the parents' combined net income and on the time share. Under § 4055(b)(3), you start with one plus H% (if the higher earner has the children 50 percent of the time or less) or two minus H% (if more), and multiply by the fraction for your income band:

For more than one child, the one-child figure is multiplied (§ 4055(b)(4)): by 1.6 for two children, 2 for three, 2.3 for four, 2.5 for five, and on up to 2.86 for ten.

A worked example

Suppose the higher earner nets $6,000 a month and the lower earner nets $3,000. The children live mostly with the lower earner, and the higher earner has them 20 percent of the time.

1. TN = $6,000 + $3,000 = $9,000. That falls in the $5,001–10,000 band, so the fraction is 0.250.
2. H% = 20 percent, which is 50 percent or less, so K = (1 + 0.20) × 0.250 = 0.30.
3. HN − (H% × TN) = $6,000 − (0.20 × $9,000) = $6,000 − $1,800 = $4,200.
4. CS = 0.30 × $4,200 = $1,260 a month for one child.
5. For two children, multiply by 1.6: $2,016 a month.

This is an illustration of how the statute's arithmetic works, not a prediction for any family. Real cases start from gross income and apply the § 4059 deductions, which the software handles. Use the official calculator for a real estimate.

Notice what moves the number. More time with the children raises H%, which lowers support. Higher combined income moves the family into a band with a different fraction. And because both incomes count, a raise for the parent receiving support usually lowers the amount too.

The low-income adjustment

The 2024 overhaul of the guideline, SB 343, changed how the formula treats parents with low incomes. Under § 4055(b)(7), a parent who owes support is presumed entitled to a low-income adjustment when their net disposable income is less than what a full-time minimum-wage job pays:

(7) In all cases in which the net disposable income per month of the obligor is less than the amount of monthly gross income earned from full-time minimum wage, established by Section 1182.12 of the Labor Code, at 40 hours per week, 52 weeks per year, there is a rebuttable presumption that the obligor is entitled to a low-income adjustment.

With California's minimum wage at $16.90 an hour in 2026, the Judicial Council puts the current threshold at $2,929 a month. It was $2,773 when the new rule began on September 1, 2024, and $2,860 in 2025. The threshold moves each January with the minimum wage.

The adjustment can reduce support by up to a fraction of the guideline amount: the gap between the threshold and the parent's net income, divided by the threshold. A parent netting $2,000 a month in 2026 could see support reduced by as much as ($2,929 − $2,000) ÷ $2,929, about 32 percent. The other parent can rebut the presumption by showing the reduction would be unjust in the particular case.

A second safeguard applies on top of that. Under § 4057(b)(5), if a parent qualifies for the adjustment and the formula still takes more than half of their net disposable income, the court can reduce support by the amount above 50 percent.

When a judge can depart from the formula

The formula amount "is presumed to be the correct amount of child support to be ordered" (§ 4057(a)). Under § 4057(b), that presumption can be rebutted only on specific grounds, including:

• The parents have agreed to a different amount, following the procedure in § 4065.
• The family home's sale has been deferred and its rental value exceeds the housing costs.
• The paying parent has an extraordinarily high income and the formula amount would exceed the children's needs.
• A parent is not contributing to the children's needs in proportion to their custodial time.
• Special circumstances, such as different time-sharing for different children, substantially equal time-sharing where one parent's housing costs are much higher, or a child's special medical needs.

The judge must explain a departure in writing or on the record.

Add-ons: childcare, health costs and more

Guideline support is only the base. Family Code § 4062(a) requires two add-ons:

(1) Childcare costs, if those expenses are actually incurred, related to employment or to reasonably necessary education or training for employment skills, as described in Section 4063, unless those costs are specifically included in the guideline calculation itself. (2) The reasonable uninsured health care costs for the children as provided in Section 4063.

Under § 4062(b), a court may also order two more: educational or other special needs, and "Travel expenses for visitation."

Since September 1, 2024, the default split has changed. Section 4061(a) now divides these costs "in proportion to the parents’ net incomes," rather than presuming an even split. A parent who earns a quarter of the family's income generally pays about a quarter of the daycare.

How long child support lasts

Support generally ends at 18. Family Code § 3901(a)(1) extends it for a child still in high school:

(a) (1) The duty of support imposed by Section 3900 continues as to an unmarried child who has attained 18 years of age, is a full-time high school student, unless excused pursuant to paragraph (2), and who is not self-supporting, until the time the child completes the 12th grade or attains 19 years of age, whichever occurs first.

California does not require parents to pay for college. Parents can agree to support an adult child, including through college, and a court can approve and enforce that agreement (§ 3587). A separate duty applies to an adult child who cannot earn a living because of incapacity (§ 3910).

Changing or suspending support

A support order "may be modified or terminated at any time as the court determines to be necessary" (§ 3651(a)), usually because incomes or parenting time have changed. The timing matters: a change generally can reach back only to the date the request was filed (§§ 3651(c), 3653(a)). A parent who loses a job and waits months to file cannot erase the support that built up in the meantime. File promptly, even before you know the outcome.

If the paying parent is incarcerated or involuntarily institutionalized for more than 90 consecutive days, support is suspended by operation of law unless they have the means to pay (§ 4007.5(a)). It resumes on the first day of the tenth month after release.

The state calculator and the child support agency

The California Department of Child Support Services publishes a free guideline calculator. The Judicial Council's list of certified calculators, updated August 10, 2026, shows it as recertified. Courts and lawyers often use commercial programs certified under Cal. Rules of Court, rule 5.275; they apply the same statute.

Either parent can also open a case with their local child support agency, which can establish paternity, set support and enforce it through wage withholding. Under Family Code § 17406, the agency represents "the public interest in establishing, modifying, and enforcing support obligations"; it is not either parent's lawyer.

Frequently asked questions

How is child support calculated in California?

By the statewide formula in Family Code § 4055: CS = K[HN − (H%)(TN)]. It uses both parents' net incomes and the percentage of time each has the children. The result is presumed correct unless a listed exception applies.

How much is child support for one child in California?

There is no fixed percentage. In our worked example, a parent netting $6,000 a month with the child 20 percent of the time, facing a parent netting $3,000, would pay about $1,260 a month. Your figure depends on both incomes and the time share; use the state's calculator.

Does 50/50 custody mean no child support in California?

Not necessarily. With equal time, H% is 50 percent, but if one parent earns more, the formula still usually produces a payment from the higher earner to the lower earner.

What is the low-income adjustment for 2026?

A parent who owes support and nets less than a full-time minimum-wage income is presumed entitled to a reduction. With the 2026 minimum wage of $16.90 an hour, the Judicial Council puts the threshold at $2,929 a month.

Who pays for daycare and medical bills?

Childcare needed for work or job training, and reasonable uninsured health costs, are mandatory add-ons under § 4062. Since September 1, 2024, they are divided in proportion to the parents' net incomes unless the court orders otherwise.

Does child support continue through college in California?

No. It ends at 18, or at 19 for an unmarried full-time high-school student who is not self-supporting, whichever comes first. Parents can agree to more, and a court can enforce that agreement.

Can child support be changed after the divorce?

Yes, at any time the circumstances justify it, by filing a request with the court. A change usually reaches back only to the filing date, so file as soon as your situation changes.

Is there an income cap on California child support?

No. The formula has no ceiling. For a parent with an extraordinarily high income, a court can depart downward if the formula amount would exceed the children's needs.

Where these sections live

• Family Code § 3587 — Agreements to support an adult child
• Family Code § 3651 — Modification
• Family Code § 3901 — Support after 18
• Family Code § 4007.5 — Suspension during incarceration
• Family Code § 4055 — The guideline formula
• Family Code § 4057 — When the formula can be departed from
• Family Code § 4061 — Dividing add-on costs
• Family Code § 4062 — Add-on costs
• Judicial Council: guideline support calculators and the low-income threshold