How Child Support Is Calculated in California
Every California court starts from the same statewide formula. Once you know its four inputs, the number stops being a mystery.
California child support uses one statewide formula in Family Code 4055: CS = K[HN − (H%)(TN)]. It compares the higher earner's net income (HN) to both parents' combined net income (TN), weighted by how much time the higher earner has the children (H%). The more you earn relative to the other parent, and the less time you have the kids, the more you pay.
The formula in plain English
The guideline has four inputs:
- HN: the higher earner's net monthly disposable income.
- TN: both parents' net monthly disposable income added together.
- H%: the share of time the higher earner has primary physical responsibility for the children.
- K: how much of the combined income goes to the children. It depends on TN and on the time share.
The result is positive when the higher earner pays and negative when the lower earner pays. That happens when the higher earner has most of the custodial time.
What counts as net disposable income
Start with income from almost any source: wages, overtime, bonuses, self-employment, rental income, investment income, even unemployment and disability benefits. Then subtract what Family Code 4059 allows: federal and state income taxes, Social Security and Medicare, SDI, mandatory retirement contributions, health insurance for you and the children, child or spousal support you actually pay for other relationships, and certain job-related expenses. Courts use each parent's real tax situation, which is why two families with the same gross pay can get different results.
How custody time changes the amount
Time share enters twice: in H% directly and inside K. When the higher earner has the children less than half the time, K is (1 + H%) times the income fraction. When they have them more than half the time, it becomes (2 − H%). At a true 50/50 split with equal incomes the result is zero. But equal time alone doesn't cancel support: the parent who earns more still usually pays.
The K factor and income bands (since September 1, 2024)
The fraction inside K depends on combined net income. The bands were changed by SB 343:
| Combined net income (TN) per month | Fraction |
|---|---|
| $0–$2,900 | 0.165 + TN ÷ 82,857 |
| $2,901–$5,000 | 0.131 + TN ÷ 42,149 |
| $5,001–$10,000 | 0.25 |
| $10,001–$15,000 | 0.1 + 1,499 ÷ TN |
| Over $15,000 | 0.12 + 1,200 ÷ TN |
A worked example
Parent A nets $8,000 a month and has the children 20% of the time. Parent B nets $2,000. Combined net income is $10,000, so the fraction is 0.25 and K = (1 + 0.2) × 0.25 = 0.3.
CS = 0.3 × ($8,000 − 0.2 × $10,000) = $1,800 a month for one child, paid by Parent A. For two children, the law multiplies it by 1.6: $2,880.
More than one child
The one-child amount is multiplied by a factor set in the statute: 1.6 for two children, 2 for three, 2.3 for four, up to 2.86 for ten. The order assigns the one-child amount to the youngest child and the difference to each older child, so support steps down as children age out.
Low-income adjustment
If the paying parent's net income is below what full-time minimum wage earns (about $2,929 a month at the current state minimum wage), the law presumes the court should reduce the amount, by up to the support amount × (that monthly figure − the payer's net) ÷ that monthly figure.
Add-ons and when courts deviate
On top of the guideline, courts must add child care costs related to work or job training and uninsured medical costs, usually split 50/50 unless ordered otherwise (Family Code 4062). A court can deviate from the guideline only in limited situations listed in Family Code 4057, such as a parent with extraordinarily high income or a parties' stipulation.
Changing an order
Support can be modified when circumstances change: job loss, a raise, a new custody schedule. The new amount is recalculated with the same formula and usually starts from the date the request was filed, so file promptly.
Run your numbers
Our California Child Support Calculator applies this exact formula, including the income bands, the multiple-children multiplier and the low-income adjustment. You can enter net income directly or estimate it from gross pay.
Frequently Asked Questions
What percentage of income is child support in California?
There is no flat percentage. The guideline formula uses both parents' net incomes and the custody time share. The share of combined net income set aside for the children (the fraction inside the K factor) ranges from about 0.165 to 0.25 depending on income, and is then adjusted for the time share.
Does 50/50 custody mean no child support in California?
Only if both parents earn about the same. With equal time, the parent with higher net income usually still pays support under the guideline formula.
Is child support based on gross or net income in California?
Net disposable income: gross income from almost all sources minus taxes, FICA, SDI, mandatory retirement, health insurance and certain other deductions allowed by Family Code 4059.
Can child support be more than the guideline amount?
Yes. Courts add mandatory child care and uninsured medical costs, and may order discretionary add-ons for education or travel. They can also deviate from the guideline in limited situations under Family Code 4057.
How long does child support last in California?
Generally until the child turns 18, or 19 if the child is still a full-time high school student and not self-supporting. Parents can agree to longer support, and support for an incapacitated adult child can continue.
This article is for general information only and is not legal advice. Courts calculate support with certified software using each parent's full financial information. Talk to a family law attorney or your local child support agency about your case.