The new California child support law, Senate Bill 343, took effect on September 1, 2024 and rewrote the statewide guideline formula that courts use to set support. It updated the K factor that determines how much of parental income goes toward support, tied the low-income adjustment to the state minimum wage instead of a fixed dollar figure, and changed the default split for childcare and uninsured medical costs from 50/50 to a share proportional to each parent’s income.1California State Assembly. SB 343 – Child Support If you already have a support order, it was calculated under the old rules and will not update on its own. A modification has to be filed.
The Three Core Changes
SB 343 revised the uniform guideline in three places that matter for almost every case.
The K factor, which sets the percentage of combined parental income allocated to child support, was recalibrated across every income band, and a new band was added. The low-income adjustment, which protects lower-earning paying parents from an unsustainable order, is no longer anchored to a static number written into the code. And the mandatory add-on expenses that sit on top of the base support amount now default to a proportional split rather than an even one.1California State Assembly. SB 343 – Child Support
Even if neither parent’s income has changed since the last order, the new formula can produce a different number. Sometimes higher, sometimes lower, depending on where the incomes fall.
The Low-Income Adjustment Now Follows the Minimum Wage
Before SB 343, the low-income threshold sat at a fixed dollar amount that had not kept up with the cost of living. The new law scraps the static figure and ties the threshold to full-time earnings at California’s statewide minimum wage: the hourly rate multiplied by 40 hours per week, 52 weeks per year, divided by 12.1California State Assembly. SB 343 – Child Support California’s minimum wage is $16.90 per hour as of January 1, 2026, which puts the monthly threshold at roughly $2,929.2California Department of Industrial Relations. Minimum Wage The threshold will move automatically every time the minimum wage rises, without any further legislative action.
When the paying parent’s net disposable income falls below that threshold, a rebuttable presumption applies: the court presumes the parent qualifies for a reduced amount. The other parent can rebut that presumption with evidence showing the reduction would be unjust in the specific case.1California State Assembly. SB 343 – Child Support If the lowest amount under the low-income adjustment still exceeds 50 percent of the paying parent’s net disposable income, the court can reduce it further.3California Legislative Information. California Code, Family Code FAM 4057
The Revised K Factor and the Base Formula
California calculates base child support using the formula CS = K[HN − (H%)(TN)], where HN is the higher-earning parent’s net monthly disposable income, TN is the parents’ combined net monthly disposable income, and H% is the higher earner’s share of parenting time.4California Legislative Information. California Family Code 4055 The K factor is the piece SB 343 changed.
The current K factor table by combined monthly net income:
- $0–$2,900: K = 0.165 + TN/82,857
- $2,901–$5,000: K = 0.131 + TN/42,149
- $5,001–$10,000: K = 0.250
- $10,001–$15,000: K = 0.10 + 1,499/TN
- Over $15,000: K = 0.12 + 1,200/TN
At lower combined incomes the K factor is smaller, so a smaller share of income goes to support. As income rises, the share increases and then plateaus at 25 percent before scaling back down at the top. Two parents with the same numbers they had before SB 343 can now land at a materially different result.4California Legislative Information. California Family Code 4055
Add-on Expenses Now Split by Income Share
The base amount from the formula does not cover everything. California requires two add-ons on top of it: childcare related to a parent’s work or job training, and uninsured healthcare costs including co-pays, deductibles, prescriptions, and any medical, dental, or vision expenses insurance does not pay. Courts can also order additional support for educational or special needs expenses and for visitation-related travel, though those are discretionary.5California Legislative Information. California Code Family Code 4062
Under the old rule, the mandatory add-ons were split 50/50 unless someone asked the court for a different arrangement and backed it up with documentation. SB 343 flips the default. The presumptive split is now proportional to each parent’s net income: if one parent earns 70 percent of the combined net income, that parent covers 70 percent of childcare and uninsured medical bills.6California Department of Child Support Services. SB 343 Amendments – Handout Either parent can still argue for a different apportionment, but the starting point has moved.
Income Imputation and a 2026 Update
A parent who quits or takes a deliberately low-paying job to shrink a support obligation cannot escape the formula that way. When a court finds a parent voluntarily unemployed or underemployed, it can impute income based on earning capacity rather than actual earnings, considering work history, skills, education, health, age, and the local job market. Legitimate reasons still count: documented medical conditions, an industry downturn, or caretaking responsibilities for a special-needs child. Incarceration or involuntary institutionalization cannot be treated as voluntary unemployment.7California Legislative Information. California Code, Family Code FAM 4058
Beginning January 1, 2026, the Department of Child Support Services is implementing new methods for determining earning capacity and removing the option to use presumed income when establishing support orders.6California Department of Child Support Services. SB 343 Amendments – Handout
Getting an Existing Order Recalculated Under the New Law
An existing order stays in force until a court changes it. Informal agreements between parents do not count as modifications. The court can make a new order retroactive only to the date the modification request is filed, not earlier, so every month of delay is a month the old amount keeps running.
The formal petition is a Request for Order (FL-300), filed in the county that issued the original order, together with an Income and Expense Declaration disclosing income, taxes, insurance premiums, and monthly expenses.8California Courts. Request for Order FL-300 Recent pay stubs, W-2s, and tax returns go in with the paperwork. Financial disclosures are signed under penalty of perjury, so the numbers need to be accurate. In the reason for the request, cite SB 343 as the change in circumstances so the court understands the prior order was calculated under an outdated formula.
The filing fee is $60 if the modification is a motion in an existing case, or $435 to $450 if these are the first papers filed. A fee waiver is available for parents who cannot afford it.9California Courts. Ask for or Change Child Support – Section: File Your Forms After filing, the other parent has to be served by someone at least 18 years old who is not a party to the case, and the court sets a hearing where a judge or commissioner runs the new numbers through the revised formula and issues a new order.
When Child Support Ends
SB 343 did not change when support terminates. The obligation ends when the child turns 18, with one extension: if the child is still an unmarried, full-time high school student who is not self-supporting, support continues until they finish 12th grade or turn 19, whichever comes first.10California Legislative Information. California Family Code 3901 A documented medical condition that prevents full-time attendance can excuse the enrollment requirement without cutting off support.
Support can extend indefinitely for an adult child of any age who is incapacitated from earning a living and lacks sufficient means to support themselves. Both parents share that duty equally, to the extent of their ability, and any government benefits the adult child receives are considered when the amount is set.11California Legislative Information. California Family Code 3910
Why Stopping Payments Is Not an Alternative to Modifying
If a support amount set under the old formula is unaffordable now, filing for a modification is the safe move. Simply falling behind triggers enforcement that compounds fast.
When payments are overdue by more than 30 days, a notice goes automatically to California licensing agencies. After the first notice, a parent has 150 days to respond before license suspension; if it happens again, only 30 days. Suspension can hit driver’s licenses, professional licenses in fields such as medicine, law, and cosmetology, and recreational licenses for hunting, fishing, and boating. A low-income exemption protects the driver’s license only, when annual income falls below 70 percent of the county’s median, and it does not shield professional or recreational licenses.12California Child Support Services. License Suspension
Arrears over $2,500 trigger passport denial at the federal level, with the state certifying the debt to the U.S. Department of Health and Human Services for referral to the State Department.13Office of the Law Revision Counsel. 42 USC 652 Past-due support of $500 or more can be intercepted from a federal tax refund.14Office of the Law Revision Counsel. 42 USC 664 These tools operate independently and can hit at the same time. Filing for a modification when circumstances change is the way to keep the number tied to what the current law and current income actually support.