SupportSplit's California Child Support FAQ

California uses a statewide formula defined in Family Code §4055. The formula takes each parent's net disposable income (gross income minus taxes and certain deductions), the percentage of time the child spends with each parent, and the number of children. The result is the guideline support amount, which is presumptively correct unless the court finds a specific reason to deviate under FC §4057. See our guide for a full explanation of the formula.

Almost all income counts. FC §4058(a) defines gross income broadly: salary, wages, bonuses, commissions, rental income, dividends, pensions, Social Security benefits, unemployment benefits, disability insurance, and self-employment income after business expenses. The court can also impute income based on earning capacity if a parent is voluntarily unemployed or underemployed (FC §4058(b)).

Yes. With equal parenting time, support is based almost entirely on the income difference between the parents. If both parents earn the same amount and share time equally, guideline support is close to zero. If incomes are different, the higher earner still pays, but less than they would with a more unequal custody split. The relationship between parenting time and support is not linear. See the parenting time chart on our about page for a visual explanation.

Usually yes, if there is an income difference. Equal parenting time does not mean zero support. The guideline formula accounts for the income gap between parents. The parent with the higher net disposable income typically pays support even with 50/50 custody, though the amount is significantly lower than it would be with less parenting time.

Yes. Either parent can request a modification at any time by showing a material change in circumstances under FC §3651. A job loss, a significant raise, a change in parenting time, or a child aging out can all be grounds. There is no minimum waiting period. However, if the court finds the job loss was voluntary or an attempt to reduce support, it may impute income based on your earning capacity.

Generally no. Under FC §4057.5, a new spouse's or partner's income is not directly included in the child support calculation. However, it may indirectly affect things. If your new partner covers housing or other expenses, that can reduce your claimed living costs, which can come up in a hardship analysis or a request to depart from guideline.

Child support ends when a child turns 18, or at 19 if they are still a full-time high school student and not self-supporting (FC §3901). For multiple children, support steps down as each child ages out. It does not end all at once unless all children reach the age limit at the same time. Support also terminates upon a child's marriage, emancipation, or entry into active military duty.

The guideline formula in FC §4055 does not vary by age. A three-year-old and a sixteen-year-old produce the same guideline support amount for the same incomes and parenting time. The legislature chose a formula based on parental income and time, not on the specific expenses of raising children at different ages. Support ends at 18 (or 19 per FC §3901), but it does not increase or decrease as the child grows.

K is the income allocation factor in the guideline formula. It determines what fraction of the income difference between parents goes toward support. K is computed from a statutory table based on the combined net disposable income of both parents, then multiplied by a parenting time adjustment. Higher combined income generally produces a lower K, and more equal parenting time produces a higher K. This is why the relationship between custody time and support is not a straight line. See the glossary entry for the full explanation.

Add-on expenses are child-related costs that are split between parents on top of the base guideline support amount. Mandatory add-ons include work-related childcare (FC §4062(a)(1)) and uninsured health care for the children (FC §4062(a)(2)). Discretionary add-ons include educational expenses, extracurriculars, and travel for visitation. Add-ons are divided in proportion to each parent's adjusted net income.

Yes, but only with specific findings. The guideline amount is presumptively correct under FC §4057. The court may depart from guideline if a parent's income is extraordinarily high, if a parent is not contributing to the child's needs, if a child has special needs, or in other circumstances listed in FC §4057(b). The party requesting a departure bears the burden of proof, and the court must state its reasons on the record.

Pre-tax retirement contributions like a 401(k) reduce your federal and California taxable income. This lowers the taxes in the net disposable income calculation, which increases your NDI by less than the full contribution amount. The 401(k) is not subtracted again as a separate deduction. The net effect on support depends on your marginal tax bracket. Courts may consider whether voluntary contributions are reasonable relative to the parent's historical contribution pattern.

We use the same formula (FC §4055 with SB 343 K-factor bands, effective September 2024), real 2026 federal and California tax brackets, and standard payroll deductions (Social Security, Medicare, CA SDI). In our internal testing, results for common W-2 scenarios with standard deductions have been within 5% of Judicial Council-certified tools across a range of income levels and custody arrangements. Scenarios involving itemized deductions, retirement contributions, or non-wage income may show larger differences. Our calculator has not been submitted for Judicial Council certification and has not been independently verified by a CPA or legal expert.

SupportSplit is not a Judicial Council-certified calculator, so a court will not accept our output as an official guideline calculation. However, understanding the number before you walk into court or mediation is useful. You can use it to prepare for attorney consultations, model different scenarios, and evaluate whether a proposed settlement makes sense relative to guideline. See our list of certified calculators for tools accepted in court proceedings.

All calculations run entirely in your browser. We have no ability to see the numbers you enter. Nothing is transmitted to our servers. There are no accounts, no cookies, and no tracking of your inputs.

2026 federal income tax brackets, 2026 California state tax brackets, and current FICA and SDI rates. We update brackets annually when the IRS and California Franchise Tax Board publish new rates. The calculator always displays which tax year is in use.

Yes. The guideline formula is public law. The tax brackets are public data. Basic child support estimation will always be free.

In most cases, differences are explained by deductions that our free calculator does not include: mortgage interest, 401(k) contributions, health insurance premiums, union dues, and hardship deductions under FC §4070 through §4073. For scenarios with only W-2 income and standard deductions, our results have closely matched certified tools in testing. If you find a discrepancy that is not explained by these deductions, please email info@supportsplit.com. We take accuracy seriously.

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