California Child Support Guidelines: Formula, Income, and Add-Ons

The California child support guidelines set the amount a parent pays through a statewide mathematical formula built around two inputs: each parent’s net monthly disposable income and the percentage of time each parent has primary physical responsibility for the children. The result is presumed correct in every case, and judges can depart from it only when specific statutory exceptions apply.¹

The Formula That Produces the Number

The core calculation lives in California Family Code Section 4055 and reads: CS = K[HN − (H%)(TN)]. CS is the child support amount. K is the fraction of combined parental income that goes toward supporting the children. HN is the higher earner’s net monthly disposable income. H% is the approximate percentage of time the higher earner has primary physical responsibility for the children. TN is the total net monthly disposable income of both parents combined.²

Two variables drive most of the result: what each parent earns and how parenting time is divided. A higher time-share for the paying parent lowers the support amount, because that parent already covers more day-to-day costs directly. Once the inputs are settled, the math produces a single answer. Parents can fight about what their income really is or how to count overnights, but the formula itself removes most of the judge’s discretion.

Because the guideline is presumed correct, both sides can run the numbers in advance and see roughly where they will land. That is one reason most California child support cases settle on or near the formula amount.

What Counts as Income

California defines gross income broadly. It includes wages, salaries, commissions, bonuses, rental income, pensions, dividends, interest, trust income, Social Security benefits, workers’ compensation, unemployment and disability insurance benefits, and spousal support received from someone outside the current case. The list is deliberately expansive so a parent cannot hide earning power behind a particular income category.³

Self-Employment Income

For self-employed parents, the court starts with gross business receipts and subtracts expenditures required to operate the business.³ Judges are not bound by what a tax return shows. Expenses that look personal rather than genuinely necessary for the business, like meals, mixed-use vehicle costs, or payments to family members that do not reflect real work, can be added back. Depreciation that reduces taxable income on paper without reducing actual cash flow is another common add-back. Expect the court to look past the bottom line on a Schedule C and evaluate what you actually have available to spend.

Earning Capacity for the Unemployed or Underemployed

When a parent’s income is unknown, the court must consider that parent’s earning capacity. Even when income is known, the court has discretion to substitute earning capacity if doing so serves the children’s best interests. Factors include work history, job skills, education, health, criminal record, and the local job market.³

One protective rule: a parent who is incarcerated or involuntarily institutionalized cannot be treated as voluntarily unemployed when the court sets or modifies support, regardless of the offense.³

How Net Disposable Income Is Calculated

The formula does not run on gross income. It runs on net disposable income, which is what remains after specific deductions listed in Family Code Section 4059:

Federal and state income taxes, calculated using the taxes actually payable based on filing status and dependents, not current withholding.
FICA contributions, or an equivalent amount for self-employed parents.
Mandatory union dues and retirement contributions required as a condition of employment.
Health insurance premiums for the parent and any children the parent has a duty to support, plus state disability insurance premiums.
Child or spousal support being paid under a court order to someone not involved in the current case.
Job-related expenses, if the court finds them necessary after weighing the benefit to the employee.
Hardship deductions under Sections 4070 through 4073, such as extraordinary health expenses or uninsured catastrophic losses.

These deductions are subtracted from gross annual income, then divided by 12 to produce the monthly figure that feeds the formula.⁴ Getting them right matters. Forgetting a legitimate deduction inflates your income and pushes the support figure higher than the law intends.

The Low-Income Adjustment

When the paying parent’s net disposable income falls below the gross monthly equivalent of full-time minimum wage, there is a rebuttable presumption that the parent qualifies for a low-income adjustment. The adjustment reduces the support amount by a fraction tied to how far below that threshold the income falls.²

Even then, support cannot exceed 50 percent of the paying parent’s net disposable income. The other parent can try to rebut the presumption by showing that the lowest permissible amount would be unjust, but the court must weigh that argument against the impact on both parents’ net incomes.⁵

When a Judge Can Deviate From the Guideline

The guideline amount is presumed correct, but a parent can overcome that presumption by proving one of several factors in Family Code Section 4057. A judge who deviates must explain the reasoning in writing or on the record. The recognized grounds include:

The parents have stipulated to a different amount under Section 4065.
The paying parent earns so much that the formula amount would exceed the children’s actual needs.
The family residence has not been sold and its rental value exceeds the mortgage, insurance, and property tax costs combined.
One parent is not contributing at a level that matches their share of parenting time.
Special circumstances apply, such as different time-sharing schedules for different children, substantially equal custody where one parent’s housing costs are far higher, children with special medical needs, or a child with more than two legal parents.

Deviation is the exception. Most orders follow the formula.⁵

Add-On Expenses on Top of Base Support

The guideline formula covers baseline support. Family Code Section 4062 requires the court to address certain additional costs separately. The mandatory add-ons are childcare costs related to a parent’s employment or job training, and reasonable uninsured medical, dental, and other health care costs for the children.

The court also has discretion to order add-ons for the children’s educational or special needs and for travel expenses associated with visitation.⁶ These costs are typically allocated in proportion to each parent’s income rather than split equally, though the court has flexibility.

Health Insurance

Every California child support order must include a medical support order for health insurance. If a parent has access to employer-sponsored coverage, the children must be enrolled in that plan, even if the parent declines personal coverage for themselves.⁷ The premium cost shows up as a deduction in the net disposable income calculation, which means it affects both the final support amount and who is best positioned to carry the policy.⁴

Running the Numbers Yourself

The California Department of Child Support Services provides a free online Guideline Child Support Calculator that uses the same legal formula the courts apply. It produces an estimate, not a binding figure, but it gives both parents a realistic preview of what a judge would likely order.⁸

To use it, you need each parent’s monthly gross income, tax filing status, number of dependents claimed, and time-share percentage, plus specific deductions: mandatory retirement contributions, union dues, health insurance premiums, and any existing support obligations. You can adjust inputs and watch the result shift. Small changes in time-share percentages can move the figure noticeably.

Gather documentation before you start. Recent pay stubs and the last two years of state and federal tax returns give the clearest picture of income. Self-employed parents should also have profit-and-loss statements and business tax returns ready, because the court will scrutinize business deductions closely.

How Long the Obligation Lasts

The standard rule is that support continues until the child turns 18. If the child is still a full-time high school student at 18 and is not self-supporting, the obligation extends until the child finishes 12th grade or turns 19, whichever comes first. A child with a documented medical condition that prevents full-time school attendance may still qualify for the extension without the full-time enrollment requirement.⁹

Support does not automatically end on the child’s 18th birthday. The paying parent typically needs to file a motion to terminate the order, or the order itself may specify a termination date. An order left alone can keep accruing.

For an adult child who is incapacitated and unable to earn a living, the obligation can extend indefinitely. Both parents share equal responsibility to maintain a child of any age who cannot support themselves due to a disability and who lacks sufficient means. The court may direct payments into a special needs trust to preserve the child’s eligibility for public benefits.¹⁰

1
Justia Law. California Code Family Code 4050-4076
2
California Legislative Information. California Code FAM 4055
3
California Legislative Information. California Code FAM 4058
4
California Legislative Information. California Code FAM 4059
5
California Legislative Information. California Code FAM – Section 4057
6
California Legislative Information. California Code FAM 4062
7
California Child Support Services. Health Insurance
8
California Child Support Services. Guideline Calculator
9
California Legislative Information. California Code FAM – Section 3901
10
California Legislative Information. California Code FAM 3910