California Family Code § 4055: Child Support Guideline Formula

Plain-Language Summary

California Family Code § 4055 contains California’s mandatory guideline formula for calculating child support. The formula is:

CS = K[HN – (H%)(TN)]

Where CS is the support amount; HN is the high earner’s net monthly disposable income; H% is the high earner’s approximate timeshare; and TN is both parents’ combined net monthly disposable income. The statute defines how to compute each piece, provides a schedule for K (the fraction of combined income allocated to support) based on combined income and timeshare, sets multipliers for multiple children, and gives special rules for default cases and for a low-income adjustment when the obligor’s net is below a full-time minimum-wage benchmark (Labor Code § 1182.12). Guideline is presumptively correct; courts can deviate only as permitted by statute and must make the required findings on the record.

Real-World Examples

Default/no-show setting of H%: If the higher earner is the noncustodial parent and fails to appear (with no evidence of time-share), the court sets H% to 0 for the calculation. If the higher earner is the custodial parent, H% is set to 100. This ensures the formula reflects the likely parenting time in defaults.
Multiple children: After computing guideline for one child, § 4055 multiplies by statutory factors (e.g., ×1.6 for two children; ×2.0 for three), rather than re-running a separate formula for each child.
Low-income adjustment: If the obligor’s monthly net is below full-time minimum wage, a rebuttable presumption allows a reduction from the computed amount within a defined range. Certified software must display the allowable range, and the court weighs § 4053’s principles in deciding whether to adjust.
Different time-shares across siblings: When children have different schedules, H% is the average of the high earner’s time with each child, keeping the formula coherent for a single order.
“Negative” result: If the formula yields a negative number, the lower earner pays the absolute value to the higher earner (i.e., support can run the other direction when the custodial/lower-income roles flip).

Published Case Law on § 4055

In re Marriage of Hall (Cal. Ct. App. 2000) – Reversed a percentage-of-income order that didn’t match the § 4055 formula and lacked § 4056 findings. The court reiterated judges must compute guideline and, if deviating, explain why on the record.
In re Marriage of Hubner (Cal. Ct. App. 2001) – In a high-income case, the court emphasized that guideline must be calculated on a factual basis showing the supporting parent’s actual income; only then may the court assess any deviation consistent with statute.
In re Marriage of Cheriton (Cal. Ct. App. 2001) – Reaffirmed that adherence to the statutory guideline formula is mandatory; the court must compute § 4055 and apply related statutes before considering special-circumstance deviations.
In re Marriage of Macilwaine (Cal. Ct. App. 2018) – Addressed high-income deviations and stock-option income; reinforced that guideline principles govern and any departure must meet statutory requirements and be supported by findings.
Johnson v. Superior Court (Tate) (Cal. Ct. App. 1998) – Explained that the “key financial factor” for the § 4055 formula is net disposable income, requiring reliable evidence of income for a valid guideline calculation.
Rojas v. Mitchell (Cal. Ct. App. 1996) – Emphasized the presumption that guideline support is correct and that courts must make the required statutory findings when ordering an amount that differs from § 4055’s computed result.

Full Text of California Family Code § 4055

(a) The statewide uniform guideline for determining child support orders is as follows: CS = K[HN – (H%)(TN)].

(b)(1) The components of the formula are as follows:

(A) CS = child support amount.

(B) K = amount of both parents’ income to be allocated for child support as set forth in paragraph (3).

(D) H% = approximate percentage of time that the high earner has or will have primary physical responsibility for the children compared to the other parent. In cases in which parents have different time-sharing arrangements for different children, H% equals the average of the approximate percentages of time the high earner parent spends with each child.

(E) TN = total net monthly disposable income of both parties.

(2) To compute net disposable income, see Section 4059.

(3) K (amount of both parents’ income allocated for child support) equals one plus H% (if H% is less than or equal to 50 percent) or two minus H% (if H% is greater than 50 percent) times the following fraction:

Total Net Disposable
Income Per Month

$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

For example, if H% equals 20 percent and the total monthly net disposable income of the parents is $1,000, K = (1 + 0.20) × (0.165 + 1,000/82,857), or 0.21. If H% equals 80 percent and the total monthly net disposable income of the parents is $1,000, K = (2 – 0.80) × (0.165 + 1,000/82,857), or 0.21.

(4) For more than one child, multiply CS by:

2 children — 1.6
3 children — 2
4 children — 2.3
5 children — 2.5
6 children — 2.625
7 children — 2.75
8 children — 2.813
9 children — 2.844
10 children — 2.86

(5) If the amount calculated under the formula results in a positive number, the higher earner shall pay that amount to the lower earner. If the amount calculated under the formula results in a negative number, the lower earner shall pay the absolute value of that amount to the higher earner.

(6) In any default proceeding where proof is by affidavit pursuant to Section 2336, or in any proceeding for child support in which a party fails to appear after being duly noticed, H% shall be set at zero in the formula if the noncustodial parent is the higher earner or at 100 if the custodial parent is the higher earner, where there is no evidence presented demonstrating the percentage of time that the noncustodial parent has primary physical responsibility for the children.

H% shall not be set as described in paragraph (3) if the moving party in a default proceeding is the noncustodial parent or if the party who fails to appear after being duly noticed is the custodial parent. A statement by the party who is not in default as to the percentage of time that the noncustodial parent has primary physical responsibility for the children shall be deemed sufficient evidence.

(7) In all cases in which the net disposable income per month of the obligor is less than the amount of monthly gross income earned from full-time minimum wage, established by Section 1182.12 of the Labor Code, at 40 hours per week, 52 weeks per year, there is a rebuttable presumption that the obligor is entitled to a low-income adjustment.

The presumption may be rebutted by evidence showing that the application of the lowest amount of child support permitted pursuant to this paragraph would be unjust and inappropriate in the particular case. In determining whether the presumption is rebutted, the court shall consider the principles provided in Section 4053, and the impact of the contemplated adjustment on the respective net incomes of the obligor and the obligee.

The low-income adjustment shall reduce the child support amount otherwise determined under this section by an amount that is no greater than the amount calculated by multiplying the child support amount otherwise determined under this section by a fraction, the numerator of which is the amount of monthly gross income earned from full-time minimum wage, established by Section 1182.12 of the Labor Code, at 40 hours per week, 52 weeks per year, minus the obligor’s net disposable income per month, and the denominator of which is the amount of monthly gross income earned from full-time minimum wage, established by Section 1182.12 of the Labor Code, at 40 hours per week, 52 weeks per year.

(8) Unless the court orders otherwise, the order for child support shall allocate the support amount so that the amount of support for the youngest child is the amount of support for one child, and the amount for the next youngest child is the difference between that amount and the amount for two children, with similar allocations for additional children.

However, this paragraph does not apply to cases in which there are different time-sharing arrangements for different children or where the court determines that the allocation would be inappropriate in the particular case.

(c) If a court uses a computer to calculate the child support order and the obligor’s income qualifies for a low-income adjustment, the computer program shall provide the range of the adjustment permitted by paragraph (7) of subdivision (b).

(d) This section shall be operative September 1, 2024.

(Repealed (in Sec. 2) and added by Stats. 2023, Ch. 213, Sec. 3. (SB 343) Effective January 1, 2024. Operative September 1, 2024, by its own provisions.)

*Nothing on this page should be considered legal advice. This is simply a summary of information found on the Internet. Use at your own risk. This information has not been evaluated by an attorney, and it may be incorrect or obsolete due to changes in the law.