How is child support calculated in California?

By a statewide mathematical formula, not judicial hunch. Family Code section 4055 sets the uniform guideline: an algebraic formula built primarily on both parents' net disposable incomes and the percentage of time each parent has primary physical responsibility for the children. Courts and the Department of Child Support Services run it through certified calculator software. The guideline amount is presumptively correct (Family Code section 4057); judges may depart only in limited situations, such as extraordinarily high income or a stipulated different amount that serves the child's interests. On top of base support, section 4062 adds mandatory items — half of reasonable child-care costs for work and uninsured health-care costs — and discretionary add-ons like extracurriculars. Support generally continues until the child turns 18 (19 if still in high school full-time, Family Code section 3901). Either parent can seek modification whenever income or timeshare changes materially; arrears, once accrued, cannot be retroactively forgiven.

Authority: Cal. Fam. Code § 4055