Calculate child support using California's algebraic K-formula with parenting time built directly into the equation
Free calculator based on California Family Code § 4055 as revised by SB 343 (operative September 1, 2024). California uses a unique algebraic formula — CS = K × [HN - (H% × TN)] — that operates on each parent's net disposable income after federal taxes, CA state taxes, FICA, SDI, and statutory deductions. Parenting time is built continuously into the formula with no overnight threshold, and the formula automatically determines which parent pays based on the sign of the result.
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> **Important:** This page provides general information about how California calculates child support. It is not legal advice. Every family's situation is different, and you should consult a licensed California family law attorney before making any decisions about your case. ---
California uses a math formula set by state law — the same formula applies in every California court. The formula takes into account how much each parent earns after taxes and how much time each parent spends with the children. The more you earn relative to the other parent, and the less time you spend with the children, the more you are likely to pay. Because the formula uses after-tax income, it automatically adjusts for differences in each parent's tax situation. The formula was significantly updated in 2024 (Senate Bill 343), and every California court is required to follow it unless there is a very specific legal reason to depart. ---
California casts a wide net. Income includes wages, salary, overtime, bonuses, commissions, tips, self-employment earnings, rental income, interest and dividends, Social Security benefits, disability payments, workers' compensation, unemployment benefits, pension payments, spousal support you receive, and military housing and food allowances. A few things are **not** counted: public assistance like CalWORKs or SSI, child support you already receive for a child from another relationship, and need-based VA benefits. If a court believes you are deliberately working less than you could be, a judge can calculate support based on what you are *capable* of earning — not just your current paycheck. However, if you are currently incarcerated, California law recognizes that as an involuntary situation, and your support obligation can be suspended during that time. ---
Parenting time is built directly into the California formula — there is no separate "shared custody" worksheet or overnight threshold to cross. The more time the higher-earning parent spends with the children, the lower the support amount generally is (and vice versa). The relationship is continuous, meaning even a few extra overnights per year can affect the result. Parenting time is measured as an approximate percentage of time, not just overnights. Courts consider all the time a parent has primary responsibility for the children, which can include time during the school day. Some counties use standardized percentages for common schedules (for example, every other weekend plus one weeknight). When parents have equal income and split time exactly 50/50, the formula produces $0 — because neither parent has a financial advantage over the other. ---
**No minimum:** The formula can produce $0, and there is no mandatory minimum monthly payment in California. **No maximum:** California does not cap child support based on income. For very high earners, however, a court *may* reduce support below the guideline if the calculated amount would be more than the child's reasonable needs — but this requires a specific written court finding and is not automatic. There is no set income ceiling, and no self-support reserve that protects a fixed amount of the payor's income — but the low-income adjustment (see below) provides meaningful protection for lower-income payors. ---
The base guideline amount covers the child's everyday living expenses. On top of that, California requires both parents to share certain additional costs, called "mandatory add-ons": - **Work-related childcare** (daycare, after-school care while you work) - **Children's health insurance premiums** (the portion covering the children) - **Uninsured medical costs** (co-pays, out-of-pocket health expenses not covered by insurance) Courts can also order optional ("discretionary") add-ons for educational expenses, special needs costs, and visitation travel. **Who pays what share?** Since 2024, California's default is that each parent pays a share of add-on costs proportional to their income. If you earn 60% of the combined income, you would generally pay 60% of add-on costs. Courts can order a different split, including 50/50. The parent who already paid the expense can request reimbursement from the other parent. You have **90 days** to make that request (this window was extended from 30 days by the 2024 law). ---
If the parent who is ordered to pay support has a net monthly income below California's minimum wage threshold (currently about $2,929/month for 2026, based on a 40-hour minimum-wage workweek), a **low-income adjustment** may apply. The adjustment does not reduce support to a fixed amount — instead, it creates a *range* of possible reductions. The judge decides how much of a reduction to grant within that range, based on the circumstances. The calculator is required by law to show both the minimum ($0 reduction) and the maximum possible reduction. Additionally, if the support order would take more than 50% of the lower-income parent's net income, the court may reduce it further on those grounds. ---
Yes. Either parent can ask the court to modify a child support order if there has been a **material change in circumstances** — such as a significant change in income, a job loss, a change in the child's needs, or a major change in parenting time. There is no specific dollar or percentage threshold that triggers a modification — it depends on the facts. The California Department of Child Support Services (DCSS) can also review existing orders every three years. A modification generally takes effect from the date the request was filed with the court, not from the date circumstances actually changed — so acting promptly matters. ---
Child support typically ends when the child turns **18**. However, it continues until age **19** if the child is: - Still in high school full-time, - Not self-supporting, and - Still living with a parent. For a child with a disability or other incapacitating condition who is unable to earn a living and is not self-sufficient, a parent's duty to support can continue **indefinitely** past age 18. Parents can also agree to extend support beyond these limits, and if that agreement is made part of a court order, it is legally enforceable. California does not have a general rule requiring support for college expenses. ---
A new spouse's income is **not** counted as income for child support purposes — it belongs to the new spouse, not the parent. However, if a parent files their taxes as "married filing jointly" with a new spouse, that does affect their tax bracket and therefore their after-tax income, which the formula does use. So remarriage can indirectly affect the support calculation through its effect on taxes, but the new spouse's paycheck cannot be directly added to the parent's income. ---
Self-employment income is handled differently in California. Instead of using a W-2 salary, courts look at gross business receipts minus legitimate ordinary and necessary business expenses. Self-employed parents also pay a higher Social Security/Medicare tax rate (15.3% versus the 7.65% that employees pay), which is deducted before arriving at net income. California courts closely scrutinize self-employment income and business expense deductions. A forensic accountant is sometimes brought in to determine a self-employed parent's true income. If you or the other parent is self-employed, the support calculation is more complex and the outcome is harder to predict without a review of the business financials. ---
California law (Family Code § 4057.5) requires courts to take domestic violence history into account when making child support orders. This is not optional — the court must consider it. If domestic violence is a factor in your case, this is an important area where having an attorney is especially valuable. --- *This information reflects California law as of September 2024 (SB 343) and general tax guidance applicable in 2025–2026. Laws and tax rates change. Always consult a licensed California family law attorney for advice specific to your situation.*
Free child support calculators for all 50 states coming soon
This calculator provides estimates based on California state guidelines. Actual court orders may differ based on individual circumstances. Consult with a qualified family law attorney for advice specific to your situation.