California Child Support Guidelines: How the Formula Works

California child support guidelines set a presumed monthly payment using a statewide formula built on two inputs: each parent’s net disposable income and the percentage of time the higher-earning parent spends with the child. A judge will order the guideline number unless one parent proves a different amount is more appropriate.¹

The Formula

Family Code Section 4055 states it as CS = K[HN − (H%)(TN)].¹ Each variable does specific work:

CS is the monthly child support amount.
K is the fraction of combined parental income allocated to child support. It’s set on a sliding scale: families earning under $2,900 per month have a higher percentage allocated to support than families earning over $15,000, and K also rises as the higher earner’s time-share increases.
HN is the higher earner’s net monthly disposable income.
H% is the approximate percentage of time the higher-earning parent has primary physical responsibility for the child.
TN is both parents’ combined net monthly disposable income.

For more than one child, the formula result is multiplied: 1.6 for two children, 2.0 for three, 2.3 for four, scaling up to 2.86 for ten. The multiplier doesn’t double with each additional child because housing, transportation, and utilities are shared.¹

Because the sliding K hits lower-income families proportionally harder, a separate low-income adjustment exists to pull the number back down when the paying parent earns little. More on that below.

What Counts as Income

Family Code Section 4058 defines gross income broadly. Wages, salaries, commissions, bonuses, rental income, dividends, pensions, interest, trust income, workers’ compensation, unemployment benefits, disability insurance, Social Security, severance pay, veterans benefits not based on need, and military allowances for housing and food all count. So does net income from a business after legitimate operating expenses.²

Two things are excluded: child support received for other children, and public assistance based on financial need. Spousal support received from someone outside the current case does count.²

When a Parent Isn’t Working

If a parent’s income is unknown, the court must consider earning capacity instead. Even when income is known, the court can substitute earning capacity if the parent appears to be deliberately underemployed and the switch serves the child’s best interests. Factors include work history, job skills, education, health, criminal record, the local job market, and prevailing wages in the area.²

Incarceration or involuntary institutionalization cannot be treated as voluntary unemployment. A parent in prison can seek a modification based on their actual reduced income, regardless of the crime that put them there.²

From Gross Income to Net Disposable Income

The formula doesn’t run on gross earnings. It uses net disposable income, which is gross minus a specific set of deductions in Family Code Section 4059:

Federal and state income taxes, based on actual liability for the parent’s real filing status and dependents rather than current paycheck withholding.
Social Security and Medicare contributions (FICA): the employee’s share, or an equivalent amount for the self-employed.
Mandatory union dues and retirement contributions, when required as a condition of employment.
Health insurance premiums for the parent and any children the parent is obligated to support, plus state disability insurance premiums.
Existing support obligations paid under a separate court order for people outside the current case.
Hardship deductions for situations like supporting children from other relationships or extraordinary health expenses, at the court’s discretion.

Necessary and reasonable job-related expenses can also be deducted.³ These deductions matter more than most people expect. A $500 monthly swing in net disposable income can move the support amount by hundreds of dollars, so getting them right is the single biggest lever most parents have over their number.

How Custody Time Factors In

H% is the share of time the higher-earning parent has the child, converted from the custody schedule into an annual percentage. A parent who has the child every other weekend lands around 20 percent. A true 50/50 split produces an H% of 50. When parents have different time-sharing for different children, the court averages across all children.¹

As the higher earner’s time-share goes up, the payment generally goes down, because that parent is already spending directly on the child during custodial time.¹ If the paper visitation schedule says every other weekend but the higher earner actually keeps the child three nights a week, the real schedule should be presented to the court. The gap between ordered custody and reality is one of the most common sources of disputes in support hearings.

Add-On Costs on Top of the Base Amount

The guideline number isn’t the whole bill. Family Code Section 4062 creates two categories of additional expenses handled on top of it.⁴

The court must order shared payment of mandatory add-ons:

Childcare costs tied to a parent’s employment or job training, unless already built into the guideline calculation.
Uninsured healthcare: deductibles, co-pays, dental, orthodontics, therapy, prescriptions, and other reasonable medical costs insurance doesn’t cover.

The court may order shared payment of discretionary add-ons, including educational or other special needs of the child and travel costs for visitation when parents live far apart.⁴

Add-ons are not split 50/50 by default. Family Code Section 4061 divides them in proportion to each parent’s net disposable income unless a parent requests a different arrangement or the court finds one appropriate. A parent earning 70 percent of the combined net income pays 70 percent of the add-ons.⁵

When one parent pays an add-on upfront, they provide an itemized statement to the other parent within 90 days. The reimbursing parent then has 30 days to pay their share, or whatever timeline the court set. A parent who disagrees with the amount must pay first and dispute it in court afterward; there is no right to withhold payment while arguing about the bill.⁶

The Low-Income Adjustment

When the paying parent’s net disposable income falls below the gross monthly equivalent of full-time minimum-wage work (40 hours a week, 52 weeks a year, at California’s minimum wage), a rebuttable presumption kicks in that the parent qualifies for a reduced obligation. The adjustment prevents the formula from consuming so much of a low-income parent’s paycheck that they can’t cover basic living expenses.¹

The court can still deviate upward if the reduced amount would leave the child’s needs unmet. And if adjusted support exceeds 50 percent of the obligor’s net disposable income, that is an independent ground for the court to lower it further under Section 4057.⁷

Grounds for a Judge to Depart From the Guideline

The guideline number carries a legal presumption that it’s correct. Overcoming it takes evidence that applying the formula would be unjust in the specific case. Family Code Section 4057 lists the recognized grounds:⁷

Both parents agreed to a different amount in a written stipulation under Section 4065.
Deferred sale of the family home, when the home’s rental value exceeds the mortgage, insurance, and property tax costs.
Extraordinarily high income, when the formula produces an amount that clearly exceeds the child’s actual needs. The court can cap support at a level that maintains the child’s standard of living without creating a windfall.
A parent not contributing at a level matching their custodial time (for example, having the child 40 percent of the time without spending proportionally on the child’s needs during that time).
Special circumstances: different time-sharing arrangements for different children, a large housing-cost disparity between parents with roughly equal custody, children with special medical needs, or a child with more than two legal parents.

The parent requesting the deviation carries the burden and must show by a preponderance of the evidence that the standard amount doesn’t fit. The judge must state the reasons for any deviation on the record or in writing.⁷

Estimating Your Own Number

The California Department of Child Support Services runs a free guideline calculator at childsupport.ca.gov that uses this same formula. It won’t produce a guaranteed figure (a judge makes the final call), but it will give you a realistic estimate once you have accurate income, deduction, and time-share numbers in front of you.⁸

Court orders are built from each parent’s Income and Expense Declaration (Form FL-150), a sworn financial statement capturing income sources, monthly expenses, assets, debts, and the deductions that drive net disposable income. “Current” means completed within the past three months.⁹¹⁰ Parents with straightforward finances (steady paycheck, no business income, no complex deductions) may be eligible to use the simpler Financial Statement (Form FL-155).¹¹ Bring your three most recent pay stubs, your most recent tax return, verification of childcare costs, and any custody or visitation schedule. Incomplete or inaccurate information on these sworn forms can produce penalties or a support order based on flawed numbers.

When the Obligation Ends

Under Family Code Section 4007, a child support obligation terminates when the contingency specified in the order occurs: the child reaches majority, marries, becomes emancipated, or dies.¹² Section 3901 sets the age of majority for support purposes at 18, extended to 19 if the child is still a full-time high school student, lives with a parent, and is not self-supporting. Support doesn’t always end automatically; parents sometimes need to file a motion to formally terminate the order.

A separate obligation under Section 3910 can continue indefinitely for an adult child who is unable to earn a living and lacks sufficient financial resources. Both parents share this duty equally, to the extent of their respective abilities, and the court can order payments made to a special needs trust rather than to the other parent to preserve eligibility for benefits like SSI.¹³

1
California Legislative Information. California Code FAM 4055 – Statewide Uniform Guideline
2
California Legislative Information. California Code FAM 4058 – Annual Gross Income of Each Parent
3
California Legislative Information. California Code FAM 4059 – Annual Net Disposable Income
4
California Legislative Information. California Code FAM 4062 – Additional Child Support
5
California Legislative Information. California Code Family Code FAM 4061 – Apportionment of Add-On Costs
6
California Legislative Information. California Code FAM 4063 – Reimbursement of Add-On Costs
7
California Legislative Information. California Code FAM 4057 – Rebutting the Presumption
8
California Child Support Services. Guideline Calculator
9
Judicial Branch of California. California Rules of Court 2026 – Rule 5.260
10
California Courts. Income and Expense Declaration FL-150
11
California Courts. Financial Statement Simplified FL-155
12
California Legislative Information. California Code Family Code FAM 4007 – Termination of Support
13
California Legislative Information. California Code FAM 3910 – Duty to Maintain Incapacitated Child