How California calculates child support

A formula, not a negotiation

California applies a statewide guideline formula, and the amount it produces is presumed to be the correct amount of support (Family Code §§ 4055, 4057). A court can depart from it only on grounds the statute lists — for example, an agreement between the parents, an extraordinarily high-earning parent, or special circumstances that make the formula unjust (Fam. Code § 4057(b)). That is why arguments about support are usually arguments about the inputs.

The two inputs that move it most are net disposable income and timeshare — the approximate percentage of time the higher earner has primary physical responsibility for the children (Fam. Code § 4055). Timeshare is the one parents can change by agreement, which is why it is so often contested. The state's official Guideline Calculator uses the same formula.

Since September 1, 2024, the formula includes a revised low-income adjustment: where the paying parent's net disposable income is below the monthly gross earnings of full-time work at the state minimum wage, there is a rebuttable presumption that the amount is reduced (Fam. Code § 4055, as amended by SB 343).

What counts as income

Broadly, income from whatever source: wages, salaries, commissions, bonuses, self-employment and business income, rents, dividends, pensions, unemployment and disability benefits, among others (Fam. Code § 4058(a)). In the court's discretion, employer or self-employment benefits can also count, taking into account any corresponding reduction in living expenses (§ 4058(a)(3)). Net disposable income is gross income less state and federal income tax, FICA, mandatory union dues and retirement contributions required as a condition of employment, health insurance premiums for the parent and the children, court-ordered support actually paid for other children or a spouse, and certain job-related expenses and hardship deductions (Fam. Code § 4059).

If a parent could earn more than they do, a court may use that parent's earning capacity instead of actual income when that is consistent with the children's best interests. It must consider the parent's specific circumstances — including employment history, skills, education, age, health, job-seeking efforts and the local job market — and it decides this on evidence rather than suspicion (Fam. Code § 4058(b)).

Add-ons

Two add-ons are mandatory: childcare costs actually incurred for employment or for reasonably necessary education or training, and reasonable uninsured health care costs for the children (Fam. Code § 4062(a)). A court may also add costs related to a child's educational or other special needs and travel expenses for visitation (§ 4062(b)). Add-ons are generally divided in proportion to the parents' adjusted net incomes unless a party asks for, or the court orders, a different split (Fam. Code § 4061).

Get the timeshare number right first

It is arithmetic, it can be disputed, and it can move the figure substantially. Our timeshare calculator computes it from your schedule, and you can check the result against the state's official Guideline Calculator.

Common questions

Does 50/50 custody mean no support?

Not necessarily. Equal time reduces the guideline amount but does not eliminate it where incomes differ, because the law's policy is that children should share in the standard of living of both parents (Fam. Code § 4053(f)).

Can we agree a different amount?

You can agree on an amount, but it is subject to court approval. A court cannot approve an amount below guideline unless both parents declare, among other things, that they understand their rights, are not acting under coercion, and that the amount meets the children's needs (Fam. Code § 4065(a)). If a local child support agency is involved, further limits apply (§ 4065(c)). An informal arrangement with no court order cannot be enforced as a support order if it breaks down.

How do I change an existing order?

By asking the court. Support is not recalculated automatically — a parent (or the local child support agency, where it is involved) has to file a request. Courts generally require a material change of circumstances since the last order (In re Marriage of Stanton (2010) 190 Cal.App.4th 547), although an order stipulated below guideline can be raised to guideline without showing one (Fam. Code § 4065(d)). A change can be made retroactive only as far back as the date the request was filed (Fam. Code § 3653(a)), so delay can matter.

Official sources

About this guide
Last reviewed September 2026 by the LA Law Hub editorial team against the official sources listed above. Laws, court rules, fees and local ordinances change, and how they apply depends on facts this guide cannot know. LA Law Hub is not a law firm. This guide is general information, not legal advice, and reading it does not create an attorney-client relationship. For advice about your own situation, speak with a lawyer licensed in California.

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