California Child Support Calculator

You're sitting down to build a post-divorce budget, and one of the biggest unknowns on the page is child support. How much will you pay or receive each month? California has a mandatory formula for answering that question, and a free online calculator to help you estimate the number before anything goes to a judge. This guide explains how the calculator works, what changed under the 2024 SB 343 guidelines, and what to do if your circumstances shift down the road.

Hello Divorce's free California child support estimator

We built our own free estimator specifically because the state's official calculator has a few friction points that make it hard to use on your own. Most notably, the state tool times out after 30 minutes of inactivity, which means losing all your data if you step away to track down a document. Our tool saves your information in real time, so there's no pressure to rush.

The Hello Divorce California Child Support Estimator walks you through income, tax bracket, and parenting timeshare inputs step by step. It produces a quick, reasonably accurate estimate so you can enter your budgeting and negotiation conversations with a real number in hand rather than guessing.

Keep in mind that any online estimator, ours included, produces an approximate figure. A certified calculator used by attorneys and courts, such as Xspouse or Family Law Software, will give a more precise result. But for early planning purposes, our free tool is a strong starting point.

How California calculates child support

California uses a mandatory guideline formula for all child support cases. Unlike some states, judges do not have wide discretion to set whatever amount seems fair to them. The guideline number is the starting point, and departures from it require documented justification.

At the heart of the formula is the relationship between three things: each parent's net disposable income after taxes and allowable deductions, the percentage of time each parent spends with the child, and a multiplier called the K-factor. The K-factor determines what share of combined net income should go toward child support, and it increases as combined income rises. Under the 2024 SB 343 updates, the K-factor brackets were adjusted for the first time in 32 years to better reflect today's economy.

Both parents are required to provide financial support. The non-custodial parent, meaning the one who spends fewer overnights with the child, typically makes a monthly payment to the custodial parent. The logic is straightforward: the custodial parent is already covering day-to-day living expenses for the child; the support payment helps equalize that financial responsibility. California child support is legally required until a child turns 18, or 19 if they are still enrolled in high school full-time. In some circumstances, parents can agree to extend support beyond those ages, and courts may order continued support for an adult child with a disability.

To run a calculation yourself, you will need financial and tax information for both parents. The state offers a free public calculator through California Child Support Services. Attorneys and courts use certified tools, and as of April 2025, the primary court-approved tools are Xspouse (the successor to the now-discontinued DissoMaster) and Family Law Software, both certified by the Judicial Council of California.

What changed under SB 343 in 2024

Senate Bill 343 took effect September 1, 2024, bringing the most significant overhaul to California's child support formula in decades. If you have a current support order or are entering negotiations now, understanding these changes is important. Here is a summary of what shifted:

• Updated K-factor brackets. The income bands used to calculate the K-factor multiplier had not been revised since 1992. SB 343 updated them to better reflect modern income levels and the actual cost of raising a child. For most middle-income families, the result is a modestly higher base support amount.
• Proportional add-on sharing is now the default. Before SB 343, the default method for splitting add-on expenses, like uninsured medical costs, childcare, and extracurricular activities, was 50/50 regardless of the income gap between parents. The new default splits those costs in proportion to each parent's net disposable income. The higher-earning parent now covers a larger share automatically unless the parents agree otherwise.
• Work-related childcare is presumed reasonable. Courts previously required parents to justify childcare costs. SB 343 created a rebuttable presumption that childcare expenses a parent actually incurs in order to work or pursue job training are reasonable. The other parent can challenge that presumption, but the burden shifted.
• Broader income definition. The law now explicitly includes severance pay, non-need-based veterans' benefits, and military housing and food allowances as gross income for support calculation purposes.
• Updated low-income adjustment threshold. The threshold for the low-income adjustment now ties to full-time earnings at the state minimum wage, currently $2,929 per month based on California's 2026 minimum wage of $16.90 per hour. Parents earning below that amount may qualify for a reduced support obligation.
• Earning capacity can substitute for unknown income. If a parent's actual income is unknown or they appear to be voluntarily underemployed, the court can now base its calculation on what that parent is reasonably capable of earning.

If you have an existing child support order that predates September 2024, the new rules apply to any modification request filed after that date. That means parents who were paying or receiving support under the old formula may see a different number if either side requests a modification now.

What factors does the calculator examine?

To use either the state tool or Hello Divorce's estimator, you will need information from both parents. Gathering everything in advance makes the process much faster. Here is what the calculator asks for:

• Children in common. The number of children the parents share and their ages. You will also indicate how many overnights each parent has annually, which is the timeshare percentage. This single factor has an outsized effect on the final number.
• Wages and salary. Gross income from employment, self-employment, rental income, bonuses, commissions, and as of September 2024, severance pay and certain military allowances. If a parent is unemployed, disability or unemployment income goes here too.
• Tax filing information. Each parent's filing status, federal and state withholding, and any deductions they claim for the children affect net disposable income, which is what the formula actually uses.
• Monthly deductions. Items such as mandatory retirement contributions, union dues, health insurance premiums, mortgage interest, property taxes, and job-related expenses not covered by the employer all reduce net income before the formula is applied.
• Other children. If either parent lives with or supports children from another relationship, that information factors in through a separate embedded calculation within the tool.
• Child-related add-ons. Health insurance premiums for the children, uninsured medical costs, work-related childcare, educational expenses, extracurricular activities, and travel costs for parenting time. Under SB 343, these are now divided proportionally by default rather than 50/50.
• Spousal support. If either parent is paying or receiving spousal support, that affects taxable income and feeds into the net disposable income calculation.

A practical note on the state's online tool: it has a 30-minute timeout. If you step away mid-session, you may lose your work. Come prepared with all documents listed above, or use Hello Divorce's estimator, which saves your inputs as you go.

Whatever number you arrive at is an estimate, not a final order. Courts use certified software, currently Xspouse or Family Law Software, to produce the official guideline figure used in proceedings. The Judicial Council maintains the current list of certified calculators on its website.

Step-by-step: how to run your estimate

Walking into any child support calculation cold is stressful. Here is a straightforward sequence to follow, whether you use the state tool or Hello Divorce's estimator.

1. 1 Gather income documents for both parents. Collect the most recent tax returns, two or three recent pay stubs, W-2s or 1099s, and documentation of any other income sources. If one parent is self-employed, a profit and loss statement is helpful.
2. 2 List all allowable pretax deductions. Mandatory retirement contributions, union dues, health insurance premiums you pay for yourself, and unreimbursed job expenses all reduce your net income before the formula is applied.
3. 3 Confirm tax filing status for both parents. Whether each parent files single, head of household, or married filing jointly affects net disposable income. Choose the status each parent expects to use in the coming year.
4. 4 Calculate parenting timeshare as a percentage. Count each parent's overnights with the children in a typical year, then divide by 365 to get a percentage. If you share time roughly equally, you may need to run scenarios with a few different percentages to see how sensitive the number is to small schedule changes.
5. 5 Add child-related add-on expenses. Enter monthly costs for the children's health insurance portion, uninsured medical costs, and work-related childcare. These are now shared proportionally by default under SB 343.
6. 6 Run the calculation and review the output. Use the Hello Divorce free estimator or the state tool to get your preliminary number. Note the breakdown between base support and add-ons, since those are negotiated separately.
7. 7 Consider whether any hardship factors apply. Situations involving unusually high necessary expenses, care for a disabled child from another relationship, or income at the low end of the scale may warrant a deviation from the guideline. This is something to discuss with an attorney.
8. 8 Save your inputs and plan to revisit. Life changes. If income, timeshare, or major expenses shift materially, the guideline amount should be recalculated. Keeping a record of what you entered makes future modifications easier to document.

If you and the other parent are trying to agree on child support without a court order, this process can be a neutral starting point. Many families find that running the numbers together, with the same inputs, resolves disagreements faster than arguing over a figure in the abstract. Working with a divorce mediator can help you reach a final agreement that both parents feel confident in.

Can you change a child support order?

Child support orders are not permanent. They reflect the circumstances at the time they were made, and life keeps moving. California courts can and do modify support when a parent demonstrates a material change in circumstances since the current order was entered.

Changes that typically qualify include:

• A significant increase or decrease in either parent's income
• Job loss or major reduction in work hours
• A change in the custody arrangement or parenting timeshare
• Incarceration (support may be set to $0 automatically after 90 days)
• A child aging out of specific expenses, such as childcare once they start school
• Significant changes in the child's needs

The modification process requires several forms and a court hearing. Here is what it looks like in practice:

1. Fill out the paperwork. Start with a Request for Order (FL-300) and an Income and Expense Declaration (FL-150). Make two copies of everything.

2. File at your county courthouse. Bring the originals and copies. A filing fee may apply depending on your case, though fee waivers are available. The clerk stamps your papers and adds a court date to the FL-300.

3. Serve the other parent. Someone who is 18 or older and not involved in the case must personally deliver a copy of the stamped papers to the other parent, along with blank FL-320 and FL-150 forms. Your server completes a Proof of Personal Service (FL-330), which you keep.

4. File your proof of service. Return to the courthouse to file the completed FL-330.

5. Attend the hearing. Show up with all your documents. The court reviews the circumstances and issues a modified order if the facts support it.

6. Get free help if you need it. Your county's Family Law Facilitator can review your documents at no charge. California Child Support Services may also be able to process a modification without going to court if your case is through the local agency.

One important timing note: modifications are generally not retroactive. They take effect from the date you file, not from when circumstances actually changed. If your income dropped or timeshare shifted months ago, filing sooner rather than later protects you from continuing to pay the wrong amount.

Have questions about child support?

Our team can walk you through your estimate, explain what the SB 343 changes mean for your case, and help you figure out what steps make sense next.