Calculation is client-side, income figures are never transmitted or stored.
How California Child Support Is Calculated
- Determine each parent's net monthly disposable income (gross income minus taxes, mandatory union dues, mandatory retirement contributions, health premiums, and support paid for other relationships).
- Combine both parents' net disposable income (TN) and identify the higher earner's income (HN) and their approximate timeshare percentage (H%).
- Compute K: (1+H% if H% is 50% or less, otherwise 2-H%) multiplied by a fraction that depends on TN — 0.165+TN/82,857 up to $2,900, 0.131+TN/42,149 from $2,901-$5,000, a flat 0.250 from $5,001-$10,000, 0.10+1,499/TN from $10,001-$15,000, and 0.12+1,200/TN above $15,000.
- Compute the 1-child support amount: CS = K × (HN − H% × TN).
- Multiply by the statutory multiplier for the actual number of children (1.6 for 2 children, up to 2.86 for 10).
- A positive result means the higher earner pays; a negative result means the lower earner pays the absolute value.
California Child Support Worksheet Walkthrough
Example: Parent A (higher earner) net income $5,000/month, Parent B net income $3,000/month, 2 children, Parent A has 20% timeshare.
- TN = $8,000/month, HN = $5,000, H% = 20%.
- TN falls in the $5,001-$10,000 bracket → fraction = 0.250.
- K = (1 + 0.20) × 0.250 = 0.30.
- CS (1 child) = 0.30 × ($5,000 − 0.20 × $8,000) = 0.30 × $3,400 = $1,020.
- 2-child multiplier ×1.6 = $1,632/month guideline child support paid by Parent A.
How This Calculator Works — Formula & Constants
Source: California Family Code (via leginfo.legislature.ca.gov) · Calcul déterministe — no AI, no arbitrary estimate.
Constants used
| Constant | Value | Source |
|---|---|---|
| K fraction, TN ≤ $2,900 | 0.165 + TN/82,857 | Cal. Fam. Code § 4055 |
| K fraction, $2,901-$5,000 | 0.131 + TN/42,149 | Cal. Fam. Code § 4055 |
| K fraction, $5,001-$10,000 | 0.250 (flat) | Cal. Fam. Code § 4055 |
| K fraction, $10,001-$15,000 | 0.10 + 1,499/TN | Cal. Fam. Code § 4055 |
| K fraction, over $15,000 | 0.12 + 1,200/TN | Cal. Fam. Code § 4055 |
| Multiplier (1 children) | ×1 | Cal. Fam. Code § 4055 |
| Multiplier (2 children) | ×1.6 | Cal. Fam. Code § 4055 |
| Multiplier (3 children) | ×2 | Cal. Fam. Code § 4055 |
| Multiplier (4 children) | ×2.3 | Cal. Fam. Code § 4055 |
| Multiplier (5 children) | ×2.5 | Cal. Fam. Code § 4055 |
| Multiplier (6 children) | ×2.625 | Cal. Fam. Code § 4055 |
| Multiplier (7 children) | ×2.75 | Cal. Fam. Code § 4055 |
| Multiplier (8 children) | ×2.813 | Cal. Fam. Code § 4055 |
| Multiplier (9 children) | ×2.844 | Cal. Fam. Code § 4055 |
| Multiplier (10 children) | ×2.86 | Cal. Fam. Code § 4055 |
Formula
HN = higher_earner_net_income
K = (H% ≤ 50% ? 1+H% : 2-H%) × k_fraction(TN)
CS_1_child = K × (HN - H% × TN)
monthly_support = CS_1_child × child_multiplier[children]
Deterministic calculation based on Cal. Fam. Code § 4055, transcribed verbatim from the statute text. Verify against California's official Guideline Calculator for a court-ready figure.
FAQ
How is child support calculated in California?
Determine each parent's net monthly disposable income (gross income minus taxes, mandatory union dues, mandatory retirement contributions, health premiums, and support paid for other relationships). Combine both parents' net disposable income (TN) and identify the higher earner's income (HN) and their approximate timeshare percentage (H%). Compute K: (1+H% if H% is 50% or less, otherwise 2-H%) multiplied by a fraction that depends on TN — 0.165+TN/82,857 up to $2,900, 0.131+TN/42,149 from $2,901-$5,000, a flat 0.250 from $5,001-$10,000, 0.10+1,499/TN from $10,001-$15,000, and 0.12+1,200/TN above $15,000. Compute the 1-child support amount: CS = K × (HN − H% × TN). Multiply by the statutory multiplier for the actual number of children (1.6 for 2 children, up to 2.86 for 10). A positive result means the higher earner pays; a negative result means the lower earner pays the absolute value.
What is the California K-factor child support formula?
California's guideline uses the algebraic formula CS = K × (HN − H% × TN), where TN is both parents' combined net disposable income, HN is the higher earner's net income, H% is their approximate percentage of time with the children, and K is a fraction that itself depends on TN (ranging roughly from 0.13 to 0.25+ depending on income level). The result is then multiplied by a statutory multiplier based on the number of children (1.6 for two children, up to 2.86 for ten).
Is California child support based on gross or net income?
Net disposable income — a specific statutory figure, not gross pay or simple take-home pay. It's gross income minus state and federal taxes, mandatory union dues, mandatory retirement contributions, health insurance premiums, and support actually paid for other relationships.
How does timeshare percentage affect California child support?
Timeshare percentage (H%) enters the formula twice: first inside the K fraction itself — K uses (1 + H%) if the higher earner has 50% or less of the time, or (2 − H%) if they have more — and second directly in the base calculation (HN − H% × TN). More time with the higher earner generally reduces the support amount owed, since it changes both the K value and the income figure being multiplied.
Methodology & Source
Formula model: algebraic kfactor. Effective 2025-09-01, guideline version 2025-CA-SB343-v1, last reviewed 2026-07-11.
Official source: California Family Code (via leginfo.legislature.ca.gov) (Cal. Fam. Code § 4055).
Courts may deviate from the guideline amount for documented reasons — this calculator shows the presumptive guideline amount only, not a court order. A separate low-income adjustment applies when the obligor's net disposable income is below full-time minimum-wage earnings (Fam. Code § 4055(b)(7)) — not modeled in this calculator; consult California's official Guideline Calculator for low-income cases.
Guideline figures transcribed from the primary source above and cross-checked against California's official calculator/worksheet for multiple test scenarios — see our verification methodology.