California does not set child support as a flat percentage of income. The state uses a statewide guideline formula that pulls in both parents’ incomes, allowable deductions, the number of children, and how much time each parent spends with the child. The closest thing to a child support percentage in California is a variable in that formula called the “K factor,” which represents the share of combined parental income allocated to support and shifts based on income level and number of children.1California Legislative Information. California Family Code 4055 Two families with identical salaries can end up with very different orders once custody schedules, deductions, and add-on costs are factored in.
Why There Is No Single Percentage
Every child support order in California begins with the same algebraic formula: CS = K[HN − (H%)(TN)].1California Legislative Information. California Family Code 4055 Courts and attorneys run the numbers through certified software rather than solving it by hand, but the pieces are worth knowing:
- CS is the monthly child support amount the formula produces.
- K is the percentage of combined parental income earmarked for child support, set by income brackets and the number of children.
- HN is the higher-earning parent’s monthly net disposable income.
- H% is the percentage of time the higher-earning parent has primary physical responsibility for the child.
- TN is the total combined monthly net disposable income of both parents.
The legislature built the formula around a few principles: both parents share a mutual duty to support their children according to ability, children should share in the standard of living of both households, and children’s needs should be met through private resources whenever possible.2California Legislative Information. California Family Code 4053 The goal is consistent, predictable results, so similar families get similar numbers regardless of which courtroom they walk into. But because so many inputs feed the formula, no one number captures what any given parent will pay.
The K Factor: California’s Version of a Percentage
When people ask about “the child support percentage” in California, the K factor is what they’re reaching for. K is the fraction of the parents’ combined net income that the law says should go toward supporting the child. It is not a single fixed number. It rises with the number of children and shifts based on the parents’ income level, so lower-income families and higher-income families don’t use the same rate.1California Legislative Information. California Family Code 4055
Until September 2024, the formula sorted parents into three broad income tiers: low, middle, and high earners. New guidelines that took effect on September 1, 2024 added a “low-middle” income bracket and tied the low-income adjustment thresholds to California’s minimum wage, with annual updates going forward.3California Department of Child Support Services. Changes to the Way Support is Calculated Working parents who earn more than poverty-level wages but still struggle financially now qualify for adjustments that previously applied only to the lowest earners. Depending on the specific incomes involved, the restructured brackets can push a support order either direction compared to what the old tiers produced.
Because K depends on income brackets that adjust each year and interacts with the other formula variables, there is no single percentage anyone can quote as “the California child support percentage.” A reliable estimate requires running your actual numbers through certified software or the state’s online calculator.
What Counts as Income
The formula starts with each parent’s gross annual income, which California defines broadly as “income from whatever source derived.” That includes salary, wages, bonuses, and commissions, plus rental income, dividends, interest, pensions, Social Security benefits, workers’ compensation, unemployment and disability benefits, severance pay, and spousal support received from someone outside the current case.4California Legislative Information. California Family Code 4058 For self-employed parents, the court looks at gross business receipts minus legitimate operating expenses.
One provision catches parents off guard. The court doesn’t have to accept a low reported income at face value. If a parent’s actual income is unknown, the court is required to consider earning capacity instead. Even when income is known, a judge has discretion to use earning capacity if a parent appears to be deliberately earning less than they could, looking at work history, job skills, education, and assets.4California Legislative Information. California Family Code 4058 This is often called imputed income, and it’s one of the most contested issues in California child support cases. A parent who quits a well-paying job or switches to part-time work without a legitimate reason may still have support calculated as though they were earning their prior salary. One exception: incarceration or involuntary institutionalization cannot be treated as voluntary unemployment.
Deductions That Shrink the Income Number
Gross income doesn’t enter the formula as-is. The law requires specific deductions to reach each parent’s net disposable income, which is the number that actually drives the calculation. Allowed deductions include state and federal income taxes based on actual filing status, FICA contributions, health insurance premiums, mandatory retirement contributions (and voluntary ones to the extent historically made), union dues and necessary job-related expenses, child or spousal support paid in another case, and hardship deductions for qualifying circumstances such as supporting other children from a different relationship.5California Legislative Information. California Family Code 4059
Net disposable income is not the same as take-home pay. Some paycheck deductions, like voluntary 401(k) contributions above historical levels or wage garnishments, may not reduce your income for child support purposes. The court’s version of your income often looks different from what hits your bank account.
How Custody Time Changes the Number
The second major driver of the formula is the time-share percentage, labeled H% when referring to the higher-earning parent. The logic is straightforward: the more time you spend with your child, the more you’re directly paying for food, housing, activities, and daily needs. A parent with a larger time-share is already covering more of those costs in real time, so the formula reduces that parent’s cash support obligation accordingly.1California Legislative Information. California Family Code 4055
Small shifts in time-share can produce noticeable swings in the support amount, which is why custody schedules matter so much in California cases. A parent moving from 20 percent to 30 percent time-share might see the obligation drop by hundreds of dollars per month, depending on incomes. There’s no single standard method for converting a custody schedule into a percentage. Some attorneys count hours over a full year, dividing the child’s total hours with each parent by the 8,760 hours in a year, while others count only overnights, dividing annual overnights by 365. The method used can shift the percentage by several points, and different software programs may handle it differently. If your schedule is unusual or disputed, pinning down the exact time-share figure before running the calculator is worth the effort.
Costs Added on Top of the Base Amount
The guideline formula covers baseline needs like food, shelter, and clothing. Certain extra expenses get stacked on top of that base.
Mandatory Add-Ons
Judges are required to order both parents to share two categories of extra costs: childcare expenses tied to a parent’s employment or job training, and the child’s uninsured healthcare costs, including co-pays, deductibles, and any medical or dental expenses not covered by insurance.6California Legislative Information. California Family Code 4062 These are non-negotiable. If either cost exists, the court must address it in the order.
The law directs that add-on expenses be divided in proportion to each parent’s net disposable income.7California Legislative Information. California Family Code 4061 If one parent earns 70 percent of the combined net income and the other earns 30 percent, that same ratio generally applies to splitting childcare and uninsured medical bills.
Discretionary Add-Ons
A judge may also order parents to share costs for a child’s special educational needs or travel expenses related to visitation, but these are not automatic.6California Legislative Information. California Family Code 4062 A parent who wants these costs in the order has to request them and show why they’re appropriate.
When a Judge Can Depart From the Guideline
The guideline amount carries a legal presumption that it’s the correct amount of support.8California Legislative Information. California Family Code 4057 A judge who departs from the formula must state on the record why the guideline amount would be unjust or inappropriate and why the different amount serves the child’s best interests. Situations that commonly justify a deviation include extremely high income cases where the guideline would far exceed the child’s reasonable needs, lopsided housing costs where parents share roughly equal parenting time but one spends a much larger or smaller share of income on housing for the child, special medical or developmental needs the formula doesn’t adequately cover, and situations where one parent’s actual spending on the child during their parenting time falls well below what the formula assumes. Deviations are the exception. Most orders follow the formula.
Getting an Actual Estimate
The California Department of Child Support Services offers a free online Guideline Calculator that uses the same legal formula applied in court.9California Child Support Services. Guideline Calculator You enter each parent’s income, tax filing information, deductions, and the parenting time split, and the tool produces an estimate. As of mid-2025, the calculator carries a notice that it has not yet been updated to reflect tax changes from the July 2025 federal budget bill, so certain tax calculations may be off. It still gives a useful ballpark figure, and the department advises that a certified calculator is also available through your local courthouse’s family law facilitator’s office.
Any calculator produces only an estimate. The county child support commissioner or family law judge makes the final determination, and the actual order may differ based on add-on costs, deviations, or disputed income figures the calculator can’t fully capture. That is the real reason California doesn’t publish a simple percentage: the number depends on inputs that only a full calculation, run on your actual facts, can produce.