California Child Support Calculator: How the Formula Works

Last reviewed: October 22, 2026. This article is general information about California law, not legal advice. Laws change and every situation is different, so talk to a licensed attorney in your state about your own case.

A child support calculator can take a lot of the fear out of the unknown. But the number it gives you is only as good as the information you put in, and it helps to understand what the calculator is actually doing. Below, you will find the California formula in plain English, a worked example, and what to do when you are ready to turn an estimate into a court order.

Contents

• The California guideline formula
• Worked example
• What counts as net disposable income
• How parenting time changes the result
• Add-ons: child care, health costs and more
• From calculator to court order
• FAQ

The California guideline formula

Every California court uses the same guideline in Family Code section 4055. For one child, the formula is:

CS = K[HN – (H%)(TN)]

• CS is the child support amount for one child.
• HN is the higher earner’s net monthly disposable income.
• TN is both parents’ total net monthly disposable income.
• H% is the approximate percentage of time the higher earner has primary physical responsibility for the children.
• K is the share of combined income allocated to child support. It equals (1 + H%) if H% is 50% or less, or (2 – H%) if H% is over 50%, multiplied by a fraction from the table below.

For more than one child, the one-child amount is multiplied: 1.6 for two children, 2 for three, 2.3 for four, 2.5 for five, and up to 2.86 for ten. If the result is positive, the higher earner pays the lower earner. If it is negative, the lower earner pays the higher earner.

The amount from the formula is presumed correct (Family Code 4057). The guideline reflects the principle that children should share in the standard of living of both parents (Family Code 4053).

Worked example

Suppose Parent A has net disposable income of $6,000 a month and Parent B has $3,000. Parent A, the higher earner, has the children 20% of the time.

1. TN = $6,000 + $3,000 = $9,000. That falls in the $5,001 to $10,000 band, so the K fraction is 0.25.
2. K = (1 + 0.20) x 0.25 = 0.30.
3. H% x TN = 0.20 x $9,000 = $1,800.
4. CS = 0.30 x ($6,000 – $1,800) = 0.30 x $4,200 = $1,260 per month for one child.
5. For two children: $1,260 x 1.6 = $2,016 per month.

Because the result is positive, Parent A pays Parent B. If the same parents shared time 50/50, K would be (1 + 0.50) x 0.25 = 0.375, and support for one child would be 0.375 x ($6,000 – $4,500) = $562.50 a month.

What counts as net disposable income

The formula uses net disposable income, not gross pay or the take-home figure on your pay stub. Under Family Code section 4059, the court starts with gross income from all sources and subtracts:

• State and federal income taxes actually payable, based on your real filing status and dependents (not just withholding)
• FICA (Social Security and Medicare) contributions
• Mandatory union dues and mandatory retirement contributions required as a condition of employment
• Health insurance premiums for you and the children you must support, and state disability insurance
• Court-ordered child or spousal support you actually pay for someone else
• Job-related expenses, if the court allows them
• Hardship deductions, if the court allows them

Hardships under Family Code section 4071 include extraordinary health expenses and uninsured catastrophic losses, and the minimum basic living expenses of other children you must support who live with you. You must prove them, and the deduction comes off your income, not off the support amount.

For bonuses, commissions and self-employment income, courts look at what is actually available for support, and parents often present income over a period of time to get a realistic picture. If a parent is not working or is earning less than they could, the court can consider earning capacity instead of actual income.

New partners and low incomes

The income of a parent’s new spouse or partner generally is not considered (Family Code 4057.5). Only in an extraordinary case, where excluding it would cause extreme and severe hardship to a child, can it come in.

If the paying parent’s net disposable income is less than full-time minimum wage earnings, there is a presumption that the parent is entitled to a low-income adjustment. With California’s 2026 statewide minimum wage of $16.90 an hour, that threshold is about $2,929 a month ($16.90 x 40 hours x 52 weeks / 12).

How parenting time changes the result

Time-share has a large effect because it appears twice in the formula. A higher H% raises K up to 50%, and it also increases the amount subtracted from HN. In the example above, moving from 20% to 50% parenting time cut support for one child from $1,260 to $562.50.

Equal time does not mean zero support. When incomes differ, the higher earner usually still pays. When parents have different time-share arrangements for different children, the court uses the average of those percentages.

Add-ons: child care, health costs and more

Under Family Code section 4062, the court must add:

• Child care costs actually incurred for employment, or for reasonably necessary education or training for employment skills
• Reasonable uninsured health care costs for the children

The court may also add costs for a child’s educational or other special needs, and travel expenses for visitation.

These add-ons are divided in proportion to the parents’ net incomes, adjusted for support being paid, unless a parent asks for, or the court orders, a different split (Family Code 4061).

From calculator to court order

Deviating from the guideline

The court can order a different amount only for reasons listed in Family Code section 4057, such as an agreement between the parents, an extraordinarily high income where the formula would exceed the children’s needs, a parent not contributing in line with their custodial time, or special circumstances like a child’s special medical needs. The court must explain its reasons.

Your Income and Expense Declaration

In court, your income is shown on the Income and Expense Declaration (FL-150). Be accurate and attach the documents it asks for. Your local child support agency can also open a case to help establish, modify or enforce support.

Changing an order later

An order stays in effect until a court changes it, even if you lose your job. A modification can generally be made retroactive only to the date you filed your request (Family Code 3653), so file as soon as your circumstances change. Unpaid support generally accrues interest at 10% a year under California’s judgment interest statute.

FAQ

How does California calculate child support?

Courts use the statewide formula in Family Code section 4055, CS = K[HN – (H%)(TN)], based on each parent’s net disposable income and the higher earner’s share of parenting time. Child care and uninsured health costs are added on top.

Is the California child support calculator accurate?

The DCSS calculator applies the same guideline courts use, so it gives a good estimate if your income and time-share inputs are accurate. Only a judge’s order sets the final amount.

Does 50/50 custody mean no child support in California?

No. With equal time, the formula still produces support when one parent earns more. In the example above, a parent earning $6,000 net would still pay $562.50 a month for one child.

Does my new spouse’s income count?

Generally no. California excludes a new spouse’s or partner’s income except in extraordinary cases where excluding it would cause extreme and severe hardship to a child.

What is the interest rate on unpaid child support in California?

Past-due support generally accrues interest at 10% a year. Your local child support agency can tell you the balance and interest on your case.

Sources: California Family Code sections 4053, 4055, 4057, 4057.5, 4059, 4061, 4062, 4071 and 3653; Code of Civil Procedure 685.010; California DCSS guideline calculator; California DIR: Minimum Wage.