California’s Child Support Formula Has Changed — And Your Existing Order May Need to Be Revisited

California’s Child Support Formula Has Changed — And Your Existing Order May Need to Be Revisited

By Kent Tierney | Tierney Law Group, PC | Pleasanton, California

For the first time since 1992, California has fundamentally overhauled the way child support is calculated. Senate Bill 343 (SB 343), signed into law in 2023 and effective September 1, 2024, represents the most significant restructuring of California’s child support guidelines in over three decades. If you have an existing child support order — or are about to go through a dissolution or custody proceeding — here is what you need to know.

Why the Formula Needed to Change

California’s child support guideline has long used a mathematical formula designed to produce consistent, predictable results across all cases. The core formula — CS = K[HN – (H%)(TN)] — has remained structurally unchanged since 1992. Under the old framework, “K” (the income allocation factor used to determine how much of combined parental income is devoted to the children) was calculated based on each parent’s gross income. The problem with that approach is straightforward: what a parent actually has available to support a child is their take-home pay, not their pre-tax earnings.

Over thirty years of inflation, rising housing costs, and an economy that looks nothing like it did in the early 1990s, the old formula increasingly produced results that bore little relationship to what families could actually afford.

What SB 343 Changes

1. Net Income Replaces Gross Income in the K-Factor

The most consequential change in SB 343 is the shift from gross to net income as the basis for the K-factor calculation. The court now looks at each parent’s net disposable income — income after taxes, mandatory deductions, and other allowable expenses — when determining the income allocation. This produces a more accurate picture of each parent’s actual financial capacity and, in most cases, results in a more equitable distribution of child support obligations between the parties.

2. Low-Income Protections Tied to Minimum Wage — Updated Annually

Under the old guidelines, the low-income adjustment threshold was a fixed figure that quickly became outdated. SB 343 ties the threshold directly to California’s minimum wage, which is reviewed and adjusted annually. As of January 1, 2026, the low-income adjustment applies to parents earning up to approximately $2,929 per month — calculated on full-time employment at the current California minimum wage of $16.90 per hour. This figure will update automatically each year as the minimum wage changes, keeping the low-income protections aligned with economic reality going forward.

This is meaningful protection for parents whose earning capacity is limited by disability, job instability, or long-term caregiving responsibilities — circumstances that the prior formula handled inadequately. Courts now have a clearer and more current baseline for determining whether a parent qualifies for a reduced support obligation under the low-income adjustment.

3. Add-On Expenses Are Now Split Proportionally

Under the prior guidelines, child support “add-ons” — expenses such as childcare costs, uncovered medical and dental expenses, extracurricular activities, and special needs — were typically split 50/50 between the parents regardless of the income disparity between them. SB 343 changes this default: add-on expenses are now allocated proportionally to each parent’s net income. The parent with significantly higher income will bear a correspondingly larger share of these recurring costs. For families where the income gap between parents is substantial, this change can materially affect total support obligations.

4. The Calculator Has Changed Too

Every California family law practitioner is familiar with DissoMaster, the Judicial Council-certified software that has calculated guideline support for decades. Effective March 31, 2025, DissoMaster was discontinued and is no longer updated. As of April 1, 2025, XSpouse is the Judicial Council-certified standard for guideline calculations in California courts. XSpouse is built to incorporate the SB 343 changes and is now the required tool for court filings. Any practitioner or party still relying on DissoMaster outputs is using a tool that does not reflect current law.

What This Means If You Have an Existing Child Support Order

SB 343 is not retroactive. Your current order remains in effect and is not automatically modified by the change in the law. However, the enactment of SB 343 and the resulting change in the guideline formula is widely recognized as a potential basis for demonstrating a “significant change of circumstances” — the legal standard required to bring a modification request before the court.

In practical terms, this means that either parent in an existing support arrangement may now have grounds to seek a modification. The recalculation under SB 343 — particularly the shift to net income and the revised low-income threshold — may produce a meaningfully different result than the prior guideline calculation. Whether that difference favors an upward or downward modification depends on the specific facts, but the point is this: if your existing order was calculated under the old gross-income formula, it may no longer reflect what the current guideline would produce.

Parents who are paying support should consider having their obligation recalculated under SB 343. Parents receiving support should do the same — the change does not necessarily favor one side. The proportional add-on allocation change, in particular, can cut either way depending on which parent bears the greater share of recurring child-related expenses.

Practical Considerations for Families

There are several immediate steps worth considering in light of these changes:

• Review your existing order. If your child support order was entered before September 1, 2024, obtain a recalculation under SB 343 to determine whether the new guideline would produce a materially different result. A difference that is not merely de minimis may support a modification request.
• Document income accurately. The shift to net income makes accurate income documentation more important than ever. Tax returns, pay stubs, benefit statements, and evidence of allowable deductions all bear directly on the net income calculation. If your income includes disability benefits, irregular employment income, or reductions attributable to caregiving obligations, those factors need to be properly presented to the court.
• Track your add-on expenses. If you are incurring recurring childcare, medical, or other qualifying add-on expenses, document them carefully. Under the new proportional allocation, the division of these costs is no longer a fixed 50/50 split — how they are characterized and supported in court can make a real financial difference.
• Do not use outdated calculations. If you are in active litigation or considering a modification, ensure your attorney is using XSpouse, not DissoMaster. Courts are applying the SB 343 guidelines, and submissions based on outdated calculations will not reflect current law.

The Bottom Line

California’s child support overhaul is long overdue. The shift to net income, the minimum-wage-indexed low-income threshold, and the proportional add-on allocation all move the formula closer to what families actually experience financially. For parents navigating new proceedings, these changes provide a more equitable starting point. For parents with existing orders, they are a prompt to take a fresh look at whether current obligations still reflect the guideline.

At Tierney Law Group, we regularly advise clients on child support calculations, modification proceedings, and the full range of family law matters. If you have questions about how SB 343 affects your situation, we welcome the opportunity to discuss it with you.

Kent Tierney is the managing partner of Tierney Law Group, PC, located in Pleasanton, California. The firm serves clients throughout the Bay Area and Northern California in family law, civil litigation, and business matters.

This article is intended for general informational purposes only and does not constitute legal advice. Reading this article does not create an attorney-client relationship. For advice specific to your circumstances, please consult a qualified California family law attorney.

Tierney Law Group, PC

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