California Child Support 101: How It’s Calculated, Changed, and Enforced (with San Diego Tips)

This guide is general information for California families and does not create an attorney-client relationship.

The Big Picture

California uses a statewide “guideline” formula to set child support so orders are more consistent and predictable across counties. Judges start with the formula and then add certain required costs (like work-related childcare and uninsured medical) and, in limited situations, may make adjustments.

How California Calculates Child Support

The guideline formula (the math behind it)

California Family Code section 4055 sets out the algebraic formula:

CS = K × [HN − (H% × TN)]

Where (in simplified terms):

• CS = support,

• K = a factor that allocates both parents’ income to child support,

• HN = the higher earner’s net disposable income,

• H% = percentage of parenting time with the higher earner,

• TN = total net disposable income of both parents.

You don’t have to memorize it—but it’s why income and parenting time drive outcomes. With legal help from Zando Law Firm in downtown San Diego, we can walk you through it every step of the way.

Special Situations That Commonly Change the Outcome

Self-employed parents & business deductions

Not all tax deductions reduce income for child support. California appellate cases hold that depreciation generally isn’t deductible for support purposes—courts often add it back to income. The principle originated in Asfaw v. Woldberhan and was extended in 2020 to certain equipment/vehicle depreciation in In re Marriage of Hein.

Imputing income (earning capacity)

If a parent is unemployed or under-employed by choice, courts may base support on earning capacity (what the parent could earn) when supported by evidence of ability and opportunity to work. See In re Marriage of Bardzik and related authorities.

High-income or changing tax bands

California periodically updates technical inputs used inside the formula (for example, the “K factor” bands were updated in 2024). If your income profile is unusual, a lawyer or a certified calculator can help model scenarios.

The fact is that calculating support can be a complicated endeavor requiring the right mix of legal prowess and understanding. There is much more that goes into support calculations than can possibly be shown here. Contact Zando Law Firm for your evaluation for further information.