Child Support Calculations in California

California uses a unique statewide guideline formula governed by Family Code §4050–4076 to calculate child support. The formula considers both parents' incomes and parenting time, producing a presumptively correct amount that courts apply in nearly all cases. Whether you're going through an uncontested or contested divorce, understanding how this calculation works is essential.

The California Guideline Formula

The core formula is: CS = K × [HN − (H% × TN)]

• CS: Child support amount
• K: Fraction of combined net income allocated to child support (based on income bracket and time share)
• HN: Higher earner's net monthly disposable income
• TN: Total net monthly disposable income (both parents combined)
• H%: Higher earner's percentage of time with the child

If CS is positive, the higher earner pays that amount. If negative, the lower earner pays the absolute value. This built-in time-share adjustment means parenting time directly affects the support amount.

Determining Income

California considers income "from whatever source derived" under Family Code §4058. This includes:

• Salaries, wages, commissions, and bonuses
• Self-employment income (gross receipts minus business expenses)
• Rental income, dividends, and interest
• Unemployment, disability, and workers' compensation
• Social Security benefits (except SSI)
• Stock options and RSUs when vested and available to sell

Net disposable income is calculated by subtracting from gross income: federal and state taxes, FICA, mandatory retirement contributions, health insurance premiums, and court-ordered support paid to others.

The K-Factor Brackets (Updated by SB 343)

Effective September 1, 2024, SB 343 updated the K-factor brackets for the first time since 1992. The K value depends on combined monthly net income (TN) and the high earner's time share (H%):

• $0–$2,900: 0.165 + TN/82,857
• $2,901–$5,000: 0.131 + TN/42,149
• $5,001–$10,000: 0.250
• $10,001–$15,000: 0.10 + 1,499/TN
• Over $15,000: 0.12 + 1,200/TN

When H% ≤ 50%, multiply the fraction by (1 + H%). When H% > 50%, multiply by (2 − H%). This adjustment recognizes that the parent spending more time with children incurs more direct expenses.

Multiple Children Multipliers

For more than one child, multiply the one-child support amount by:

• 2 children: ×1.6
• 3 children: ×2.0
• 4 children: ×2.3
• 5 children: ×2.5
• 6+ children: Continues incrementally

Estimate Your California Child Support

Use our calculator to get a preliminary estimate. For official calculations, use the Judicial Council certified calculators.

Low-Income Adjustment (LIA)

SB 343 also updated the low-income adjustment. When the obligor's net disposable income falls below full-time minimum wage (currently $2,860/month for 2025 and $2,929 for 2026), a rebuttable presumption arises for reduced support:

• Reduction formula: Base CS × [(Threshold − obligor's net income) ÷ Threshold]
• Rebuttable: Either party can argue the adjustment is unjust
• Updated annually: Tied to state minimum wage increases

Mandatory and Discretionary Add-Ons

Beyond the base guideline amount, California requires certain add-ons under §4062:

• Mandatory: Employment-related childcare costs and reasonable uninsured healthcare expenses
• Discretionary: Educational needs, special needs, and visitation travel expenses
• Apportionment: Add-ons are split proportionally based on each parent's net disposable income

Common Calculation Mistakes

• Using gross instead of net income: The formula requires net disposable income after deductions
• Ignoring irregular income: Bonuses, commissions, and stock compensation should be included (courts may use Ostler-Smith percentage orders for variable income)
• Miscalculating time share: H% is the high earner's time with children, not custody percentage
• Using outdated K-brackets: Make sure to use the post-September 2024 brackets from SB 343
• Forgetting add-ons: Childcare and uninsured medical costs are mandatory additions to base support

When to Modify Support

Child support can be modified at any time upon a material change in circumstances. Local child support agencies typically pursue modification when:

• The recalculation shows a change of at least 20% or $50/month, whichever is less
• Significant changes in income, time share, or family size occur
• A parent becomes incarcerated or institutionalized (support automatically set to $0 after 90 days)

File modification requests promptly—retroactivity typically runs only back to your filing date.

Key Takeaways

• Unique formula: CS = K × [HN − (H% × TN)] considers both income and parenting time
• SB 343 updates: New K-factor brackets and LIA threshold effective September 2024
• Net disposable income: After-tax income minus mandatory deductions
• Multiple children: Use statutory multipliers (1.6 for 2, 2.0 for 3, etc.)
• Low-income protection: LIA threshold is $2,860/month (2025), $2,929 (2026)
• Add-ons required: Childcare and uninsured medical costs are mandatory

For more information about California divorce processes, see our California divorce timeline and filing checklist.