There is no set dollar figure for child support for one child in California. Every order comes out of a statewide formula that weighs both parents’ incomes against how much time each parent has the child, so two families with the same paycheck can end up with very different numbers. A higher earner with little custody time might owe around $1,000 a month; the same salary paired with shared custody could produce a fraction of that, or nothing at all.
The rest of this article walks through how the formula reaches its number, what income and deductions go into it, and the situations where a judge can order something different.
Why There Is No Flat Amount
California law requires every court to use the same formula, written into Family Code Section 4055.1{FN1} The formula is designed to reflect two principles from Family Code Section 4053: both parents share equal responsibility for supporting their child, and the child should benefit from the standard of living of both households.2{FN3}
Because the formula runs on both parents’ actual net incomes and the actual custody split, the answer to “how much” is always specific to your case. General ranges are only useful as a rough sanity check.
The Formula and What Drives the Number
The statutory formula is CS = K[HN − (H%)(TN)].1{FN1} Each letter stands for a piece of your financial picture:
- CS is the monthly child support amount.
- K is the share of the parents’ combined income allocated to child support. For one child it lands somewhere between roughly 16% and 25% of combined net income, with lower earners on the lower end.
- HN is the higher-earning parent’s monthly net disposable income.
- H% is the percentage of time the higher-earning parent has physical custody.
- TN is both parents’ combined monthly net disposable income.
Two variables move the number more than anything else: the gap between the parents’ incomes, and the custody timeshare. As the higher earner’s custody percentage goes up, the support they owe goes down, because they are already covering more of the child’s daily costs directly.
A Worked Example
Say Parent A earns $5,000 per month in net disposable income and has the child 20% of the time. Parent B earns $3,000 per month and has the child the other 80%. Combined income is $8,000. At that level, the K factor for one child is about 0.25, adjusted upward by Parent A’s timeshare to roughly 0.30. Plugging in: CS = 0.30 × [$5,000 − (0.20 × $8,000)] = 0.30 × $3,400, or about $1,020 per month. Parent A pays that to Parent B.
Change nothing except the custody split. If Parent A had the child 50% of the time, the support amount would drop sharply, because Parent A is already spending more directly on the child’s needs.
What Counts as Income
The formula does not run on your take-home pay. It runs on “net disposable income,” which starts with a broad definition of gross income and then subtracts specific deductions the law allows.
Under Family Code Section 4058, gross income includes:3{FN5}
- Wages, salaries, bonuses, and commissions
- Self-employment earnings (gross receipts minus business operating costs)
- Unemployment and disability benefits
- Workers’ compensation
- Investment income like dividends, interest, and rent
- Pensions, Social Security benefits, and trust income
- Spousal support received from someone outside the case
The court does not count child support received for children from a different relationship, and it does not count income from need-based public assistance.3{FN5}
Deductions That Bring the Number Down
Family Code Section 4059 allows these deductions from gross income to reach net disposable income:4{FN7}
- Federal and state income taxes actually owed, not just what is withheld
- Social Security and Medicare contributions
- Health insurance premiums for yourself and your children
- Mandatory union dues and required retirement contributions
- Child or spousal support already paid under a court order for a different family
- Necessary job-related expenses, if the court approves them
- A hardship deduction for qualifying circumstances such as extraordinary medical expenses or supporting other children
Small changes here matter. A large health insurance premium or an existing support order for another child can meaningfully shift the guideline number.
When a Parent Is Not Working
Quitting a job or taking a lower-paying one will not automatically produce a lower support number. Under Family Code Section 4058(b), a court can base the calculation on what a parent is capable of earning rather than what they actually earn.5{FN_4058b} This is called imputing income.
To decide earning capacity, the court looks at work history, job skills, education, age, health, the local job market, and barriers to employment such as a criminal record.5{FN_4058b} A parent does not have to be acting in bad faith for income to be imputed. If a parent’s income is unknown, the court is required to consider earning capacity.6{FN_courts_pdf}
Two limits apply. A court cannot treat incarceration as voluntary unemployment.5{FN_4058b} And a parent receiving need-based public assistance generally will not have income imputed to them.6{FN_courts_pdf}
Low-Income Adjustment
Parents earning below full-time minimum wage get a built-in cushion. Family Code Section 4055 creates a rebuttable presumption that a low-income parent qualifies for a reduced support amount.1{FN1} The reduction scales with how far below minimum wage the parent’s net income falls. California’s minimum wage is $16.50 per hour in 2025, which is roughly $2,860 per month in full-time gross earnings. A parent whose net income falls below that has a strong argument for a reduction.
The adjustment is not automatic. The other parent can push back and argue the reduced amount is unfair in context. In practice, courts recognize that a support order should not push a parent below a basic survival level.
Estimating Your Own Number
The California Department of Child Support Services publishes a free Guideline Child Support Calculator.7{FN9} You enter each parent’s gross income, allowable deductions, filing status, and custody percentage, and the calculator applies the formula.
One caveat for now: the online calculator was temporarily decertified because it does not yet reflect tax changes from the July 2025 federal budget bill.7{FN9} You can still use it for a rough estimate, but the tax piece may be slightly off. For a certified figure, visit the family law facilitator’s office at your local courthouse, or check the Judicial Council’s website for other certified calculator options.8{FN10}
Any calculator result is only an estimate. The judge or child support commissioner has the final say on the actual order.7{FN9}
Costs Added on Top of the Base Amount
The guideline formula sets the base payment. Certain expenses get added separately under Family Code Section 4062.9{FN11}
Mandatory Add-Ons
Courts must split two categories of expenses between the parents. The first is childcare costs tied to a parent’s employment, job training, or education. The second is uninsured healthcare for the child, including co-pays, deductibles, and any medical, dental, or vision costs insurance does not cover.9{FN11}
Discretionary Add-Ons
A court may also order the parents to share costs like private school tuition, extracurricular activities, or travel for visitation.9{FN11} These are not guaranteed. The parent requesting the add-on has to convince the court it serves the child’s interests.
Add-ons are usually divided in proportion to each parent’s net income. A parent earning 65% of the combined income would typically pay 65% of the add-on. A judge can adjust that split when the circumstances call for it.
When a Judge Orders a Different Amount
The guideline number carries a legal presumption that it is correct, but it is not fixed. Family Code Section 4057 lets a court order a different amount when the formula result would be unjust or inappropriate.10{FN14} Common reasons include:
- An extraordinarily high-earning parent, where the formula amount far exceeds the child’s reasonable needs
- A child with special medical or educational needs requiring more than the formula produces
- Roughly equal custody but very different housing costs between the parents
- A parent supporting children from multiple relationships
Parents can also agree on a different amount by stipulation. Under Family Code Section 4065, a below-guideline agreement requires both parents to confirm in writing that they understand their rights, are not being pressured, and believe the agreed amount will meet the child’s needs. If a local child support agency is involved in the case, it also has to sign off.11{FN4065} A court will reject any agreement that appears to leave the child’s basic needs uncovered.
Any deviation from the guideline has to be explained in writing or stated on the record.10{FN14} That written explanation is the paper trail that lets either parent seek review later if circumstances change.