Once custody and a parenting schedule are in place, the next question is almost always: how much child support will actually be owed? California doesn’t leave this to negotiation or guesswork — it uses a fixed statewide formula that courts are required to follow in nearly every case.

Here’s how that formula actually works, what a significant 2024 legal change means for your numbers, and where to run the real calculation yourself.

Quick Answer: How California Calculates Child Support

  • California uses a mandatory statewide formula (Family Code § 4055): CS = K[HN – (H%)(TN)] — it looks intimidating, but it boils down to income and custody timeshare
  • As of September 1, 2024, Senate Bill 343 updated the guideline formula for the first time in decades — but not in the way some sites describe it (more below)
  • The custody timeshare percentage from your parenting plan directly affects the support amount, which is why this follows naturally from your custody arrangement
  • Form FL-150 (Income and Expense Declaration) is the foundation every calculation is built on
  • The result is presumptively correct — courts must use it unless a specific legal reason justifies deviating
  • Use the official state calculator rather than a third-party estimator for anything you plan to rely on

The Formula, in Plain English

The statutory formula is CS = K[HN – (H%)(TN)]. Broken down:

  • CS — the child support amount
  • K — a factor based on combined parental income and the number of children
  • HN — the higher-earning parent’s net monthly disposable income
  • H% — the percentage of time the higher-earning parent has primary physical responsibility for the children (this comes directly from your custody arrangement and parenting plan schedule)
  • TN — the combined net monthly disposable income of both parents

In plain terms: support is driven by the income gap between parents and how the actual parenting time is split. All else being equal, more time with the higher earner generally reduces the support amount, and a bigger income gap generally increases it.

What SB 343 Actually Changed in 2024 — And What It Didn’t

You may see other sites claim Senate Bill 343 “switched the calculation from gross to net income.” Having checked the actual chaptered bill text directly against the legislature’s own record: that claim is inaccurate. Net monthly disposable income (HN and TN in the formula) was already the basis of the calculation before SB 343 — that part didn’t change.

What SB 343, effective September 1, 2024, actually did:

  • Updated the K-factor income bands — the table that determines what share of income goes to support — for the first time in decades, extending the top band up to incomes over $15,000/month instead of topping out around $10,000
  • Changed the low-income adjustment threshold from a fixed dollar amount to one tied directly to full-time minimum wage earnings, so it automatically keeps pace with wage increases going forward
  • Flipped the default for splitting add-on costs like childcare and uninsured healthcare — previously split 50/50 by default, now split proportionally based on each parent’s share of income by default
  • Expanded what counts as income to explicitly include severance pay, VA benefits not based on need, and military housing/food allowances

If you’ve seen an older explainer describing this as a “gross to net” change, that’s a common but inaccurate simplification circulating online — worth knowing if you’re trying to understand what genuinely changed versus what didn’t.

What Counts as Income

Net disposable income isn’t just your paycheck. Courts generally look at:

  • Wages, salary, and self-employment income
  • Bonuses, commissions, and overtime
  • Rental income and investment income
  • Unemployment and disability benefits (with some exceptions)

Personal expenses paid through a business (a company car, certain travel, certain meals) can sometimes be added back into income for calculation purposes, even if they’re tax-deductible for other purposes — this is a common area where a parent’s claimed income and their actual financial picture diverge, and it’s often where disputes happen.

Using the Official Calculator

The California Department of Child Support Services maintains the official Guideline Calculator, built on the exact legal formula courts use. It provides only an estimate — the county child support commissioner or family law judge has final authority — but it’s the right starting point, not a third-party site’s simplified version. A downloadable user guide walks through each field if the tool itself is confusing.

More Than One Child

California doesn’t simply double the support amount for a second child. Per the multiplier table written directly into Family Code § 4055(b)(4), the one-child amount is multiplied by exactly 1.6 for two children, 2.0 for three, 2.3 for four, and so on — a scale that flattens out rather than climbing linearly with each additional child.

Add-Ons and Adjustments

Beyond the base guideline amount, courts can add specific costs on top, most commonly:

  • Childcare costs necessary for a parent to work or get job training
  • Uninsured healthcare costs for the children
  • Certain educational or special needs

There’s also a low-income adjustment. As of SB 343, this is tied directly to full-time minimum wage earnings (40 hours/week, 52 weeks/year) rather than a fixed dollar figure — currently $16.90/hour statewide, effective January 1, 2026 (confirmed against the California Department of Industrial Relations). This is designed to make sure a lower-earning parent isn’t left without enough to cover their own basic living expenses after paying support, and it adjusts automatically as the minimum wage rises.

Can the Guideline Amount Be Changed?

The guideline amount is presumed correct, and judges generally must use it — but Family Code § 4057 allows deviation in specific circumstances, such as when applying the formula would be clearly unjust given a parent’s extraordinarily high income, a child’s special needs, or certain stipulated agreements both parents and the court agree to. This isn’t automatic; a parent generally has to specifically request and justify a deviation.

How Support Actually Gets Paid

Once ordered, support is often collected through Form FL-196 (Income Withholding for Support) — commonly called a wage assignment — which directs an employer to withhold the support amount directly from a paycheck. This is standard practice, not a sign of distrust; most guideline support orders are enforced this way by default.

Prefer to run the numbers yourself right now? Use the official state calculator — it’s the same formula courts use, not a simplified third-party approximation.

Frequently Asked Questions

Does the parent with less custody time always pay support? Generally yes, but not automatically — it depends on the income gap between both parents as well as the timeshare split. In some shared-custody arrangements with similar incomes, guideline support can come out close to $0.

Is the calculator result the exact amount I’ll be ordered to pay? No — it’s a reliable estimate based on the same formula courts use, but the final number depends on verified income figures, any applicable add-ons, and the judge’s or commissioner’s review.

What if I think the other parent is hiding income? This is a common and serious issue — gathering evidence like bank statements, lifestyle evidence, or business records through the discovery process is the standard path, and this is a good area to get professional legal help with even in an otherwise DIY case.

Can child support be changed later? Yes — a significant change in either parent’s income or the custody timeshare is generally grounds to request a modification.

This article is for general information only and is not legal advice. Child support calculations depend heavily on your specific financial documentation and circumstances — for guidance specific to your situation, consult a licensed California attorney or contact your county court’s Self-Help Center, which offers free assistance.

Sources (verified September 10, 2026):

  • SB 343 — Full Bill Text, Chapter 213, Statutes of 2023 — official California Legislative Information site (leginfo.legislature.ca.gov); read in full directly: approved by Governor September 22, 2023; new § 4055 “shall be operative September 1, 2024”; confirms net income was already the formula’s basis both before and after SB 343; K-factor bands, low-income threshold mechanism (tied to minimum wage under Labor Code § 1182.12), add-on default flip to proportional-by-income, and expanded income sources all read directly from this text
  • California Child Support Guideline Calculator — California Department of Child Support Services (official tool)
  • California Family Code § 4055 (statewide guideline formula, K-factor table, and full multiplier table through 10 children) — statutory citation; confirm current text with an attorney or official legislative source before relying on specifics
  • California Family Code § 4057 (grounds for deviation from guideline) — statutory citation
  • California Minimum Wage — California Department of Industrial Relations; re-confirmed directly this session: “$16.90/hour for all employers,” effective January 1, 2026
  • FL-150 — Income and Expense Declaration — California Courts Self-Help Guide
  • FL-196 — Income Withholding for Support — California Courts Self-Help Guide

No dedicated site article exists yet for FL-150 or FL-196 individually — FL-150 in particular is referenced by this article, the forms guide, and effectively every financial-disclosure article on this site, making it a high-priority queue item.