How California Calculates Child Support
California uses a formula-driven Income Shares model with one major difference from most states: California calculates support based on net disposable income rather than gross income. This is the most mathematically complex child support formula in the country. California Family Code Section 4055 sets out the guideline formula, and courts are required to apply it in virtually every case.
Because the calculation involves net income, tax rates, deductions, and an algebraic equation, California courts rely on specialized software called Dissomaster or XSpouse to produce the guideline number. This calculator applies the same formula. Understanding how the formula works helps you interpret your result and prepare for court.
The California Child Support Formula
California's guideline uses this algebraic equation:
CS = K × [HN − (H%)(TN)]
Here is what each variable means.
CS is the monthly child support payment. K is the combined percentage of both parents' income that is allocated to supporting the children. K is not a fixed number — it increases with the number of children and varies with income level. For one child, K is approximately 0.20. For two children, it is approximately 0.25. For three children, it is approximately 0.30. HN is the higher earner's net monthly disposable income. H% is the higher earner's approximate percentage of time spent with the children. TN is the total net monthly disposable income of both parents combined.
The formula works like this: it starts with the higher earner's net income, subtracts the portion of that income that reflects their direct spending on the children during their parenting time, and multiplies the remaining obligation by K to determine the monthly support amount.
When the higher earner has more parenting time, H% is larger, which reduces the result. When the higher earner has minimal parenting time, H% is small, which increases the support obligation.
Calculating Net Monthly Disposable Income in California
Net disposable income is the most important input in California's formula. It is calculated separately for each parent.
Start with gross income. From gross income, subtract federal income taxes (calculated at your actual marginal rate and filing status). Subtract state income taxes (California's rates range from 1 percent to 13.3 percent based on income, with a 1 percent mental health services surtax). Subtract Social Security contributions (6.2 percent of wages up to $176,100 in 2026). Subtract Medicare (1.45 percent of all wages, with an additional 0.9 percent on income above $200,000). Subtract California State Disability Insurance (SDI) at 1.1 percent of wages with no cap in 2026. Subtract mandatory union dues. Subtract health insurance premiums you pay for yourself and your children.
The result is your net monthly disposable income. Two parents with similar gross incomes can have meaningfully different net disposable incomes depending on their tax filing status, deductions, and insurance costs.
What Counts as Income in California
California Family Code Section 4058 defines income broadly. It includes wages, salaries, commissions, royalties, bonuses, rents, dividends, pensions, interest, trust income, annuities, Social Security benefits, workers' compensation, unemployment compensation, disability insurance benefits, and income from any other source.
California courts can attribute income to a parent who is voluntarily unemployed or underemployed based on their earning capacity rather than their actual earnings. If the court finds that a parent is deliberately working below their potential, the judge can calculate support as if the parent earned a market-rate wage for their skills.
California also has a special rule for high earners. When combined net disposable income exceeds the top of the state's formula tables, courts have discretion to set support that meets the children's needs while not unduly burdening the paying parent. In high-income cases, support is often negotiated rather than strictly calculated.
Step-by-Step: How to Use This Calculator
Step 1 — Calculate your net monthly disposable income. Work through each deduction listed above: federal tax, California state tax, Social Security, Medicare, SDI, union dues, and health insurance. The calculator includes fields to help you work through this if you enter your gross income and filing status.
Step 2 — Calculate the other parent's net monthly disposable income. Apply the same process using their income and deductions. If you do not know their exact tax situation, the calculator can estimate based on standard assumptions for their income level and filing status.
Step 3 — Enter your parenting time percentage. This is your H% variable — the share of overnight time the higher earner spends with the children. Count your actual overnights per year and divide by 365. This is one of the most powerful variables in California's formula. A shift of 10 percentage points in parenting time can change the monthly obligation by several hundred dollars at typical income levels.
Step 4 — Enter the number of children to set the K value.
Step 5 — Review the breakdown. Confirm that the net income inputs look correct before accepting the result.
Parenting Time and California's Formula
Parenting time is built directly into the California formula through the H% variable. Unlike most states that apply a separate credit table, California integrates parenting time into the core calculation. This means every percentage point of parenting time matters.
When the higher earner has significant parenting time, the formula automatically reduces their support obligation because they are directly spending on the children during that time. At 50/50 parenting time, the H% variable is 0.5, which substantially reduces the calculated amount. If both parents have equal income and equal parenting time, the formula often produces a result of zero or near zero.
California is one of the few states where parenting time can reduce support to zero even when incomes are different, if the income difference is small and parenting time is equal.
Add-On Expenses in California
California Family Code Section 4062 divides add-ons into mandatory and discretionary categories.
Mandatory add-ons include work-related childcare costs and uninsured or unreimbursed healthcare expenses for the children. These are added to the guideline amount and split proportionally by net disposable income. Discretionary add-ons include educational costs, extracurricular activities, and travel expenses for visitation. Discretionary add-ons require a court finding that they are reasonable and necessary.
Reading Your Results
Your results will show each parent's net monthly disposable income, the K value applied for the number of children, the H% variable for the higher earner, the calculated CS amount, and add-on allocations. The final number is the monthly guideline child support obligation.
California's formula can produce very different results than you might expect from gross income alone. The net income basis and the direct integration of parenting time make it essential to enter accurate information for both parents. A $500 error in estimating net income can shift the result by $100 or more per month.
After You Get Your Estimate
California courts are required to apply the guideline formula. A judge can only deviate from the guideline in specific circumstances defined by law — for example, when both parents agree to a different amount, when applying the guideline would be unjust due to a high-income parent's circumstances, or when a parent is intentionally living below their earning capacity.
California allows modification of child support when there has been a material change in circumstances. Common triggers include a significant income change for either parent, a change in parenting time, a job loss, or a substantial change in the children's needs.
The stakes in California child support cases are high. The state's high cost of living, progressive tax rates, and income levels mean that monthly obligations are often substantial. The formula is precise, but it depends entirely on accurate net income inputs and honest reporting of parenting time.
A licensed California family law attorney can verify your net income calculation and review the result — look for attorneys offering a free initial consultation.