How Child Support Is Calculated in California
Child support in California is not a negotiation from a blank page. The state uses a single, mandatory statewide uniform guideline — an algebraic formula written into the Family Code — and the number it produces is presumed to be correct. Understanding what feeds the formula explains most of what happens in a support case.
The two inputs that drive everything
The guideline is built around two variables:
Each parent’s net disposable income. The formula starts with gross income from essentially every source — wages, self-employment, commissions, bonuses, overtime, rents, interest, disability and unemployment benefits, and more — then subtracts taxes (computed under the parent’s actual filing status), mandatory union dues and retirement contributions, health insurance premiums, and support actually paid for children of other relationships. Public assistance and, in most cases, a new spouse’s income are excluded.
The timeshare. The formula uses the percentage of time each parent has primary physical responsibility for the children. The higher the paying parent’s timeshare, the lower the support, because the formula assumes that parent is directly covering more of the children’s costs. This is why disputes about a custody schedule are frequently, underneath, disputes about support, and why the timeshare should be calculated carefully from the actual order rather than estimated.
The other inputs are the number of children and each parent’s tax filing status and deductions. The formula itself is complex enough that nobody does it by hand; the courts and the Department of Child Support Services use certified calculator software, and the state’s official calculator is available to the public online. Two parents who agree on the inputs will get the same answer from any certified calculator.
Income the court can assign
A parent who is unemployed or underemployed by choice does not reduce their obligation. The court may impute income based on the parent’s earning capacity — their ability and opportunity to work — if doing so is consistent with the children’s best interest. Self-employed parents can expect scrutiny of business deductions, and a court may treat some expenses run through a business as personal income. Where a parent’s income fluctuates, courts commonly average it over a period of time.
Add-ons
The guideline number is the base. On top of it, the court must order the parents to share:
- Child care costs related to employment or reasonably necessary education or training; and
- Uninsured health care costs for the children.
The court may also add costs of the children’s educational or special needs and travel expenses for visitation. How add-ons are divided between the parents was changed by legislation that took effect in 2024, and the allocation the court will apply depends on the parents’ relative incomes; ask how the current rule applies to your case rather than assuming an even split. Every support order also addresses health insurance, requiring a parent to maintain coverage for the children if it is available at reasonable cost.
When a judge can depart from the guideline
The guideline amount is presumed correct, and a court can order a different amount only if it makes findings that the guideline would be unjust or inappropriate in the particular case. The recognized situations include:
- The parents agree to a different amount, the agreement is in the children’s best interest, neither parent is on public assistance, and the parents are fully informed of their rights;
- The paying parent has an extraordinarily high income and the guideline 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 — for example, different timeshare arrangements for different children, or a child with special medical needs.
Outside these situations, arguments that the number is too high or too low are really arguments about the inputs. A lower-income adjustment also exists for paying parents whose net income falls below a statutory threshold that is adjusted annually.
How long it lasts
Support continues until a child turns 18, or until 19 or high school graduation, whichever comes first, if the child is still a full-time high school student living with a parent. Parents may agree to support beyond that, for example through college, and an agreement to do so is enforceable. A court may also order support for an adult child who is incapacitated and unable to be self-supporting.
Changing the order
Support can be modified whenever there has been a change in circumstances — a job loss, a substantial raise, a change in the custody schedule, a new child. The single most important rule: a modification can be made retroactive only to the date the request was filed, not to the date the circumstances changed. A parent who loses a job and waits six months to file will owe the full amount for those six months, and that arrearage cannot be forgiven. File first; sort out the details afterward.
Enforcement
Every support order includes a wage assignment directing the paying parent’s employer to withhold support from pay, although parents can agree to stay it while payments are current. Unpaid support accrues interest at 10 percent per year, does not expire, cannot be discharged in bankruptcy, and can lead to license suspensions, tax refund intercepts, passport denial, and contempt. The local child support agency will enforce an order at no charge on request, whether or not the family has ever received public assistance.
Child support and spousal support are calculated differently and interact with each other; see Spousal Support in California: How It’s Decided. For how custody schedules themselves are determined, see How California Courts Decide Child Custody.
Have a support question, or an order that no longer matches your circumstances? Ask a legal question.