DissoMaster California: How the Child Support Calculator Works

Every custody case in California eventually lands on one question: how much child support will I pay — or receive? The answer comes from a software program, and for decades, DissoMaster has been the most widely used calculator in California family courts.

Understanding what DissoMaster does — and what it cannot do — keeps you from being blindsided at your hearing.

What DissoMaster Actually Is

DissoMaster is a commercial software program certified by the Judicial Council of California to calculate guideline child support under Family Code Section 4055. Judges, attorneys, mediators, and court commissioners use it to run the mandatory statewide formula that determines monthly support obligations.

The program takes both parents' financial data and the physical custody timeshare percentage, plugs them into the statutory algebraic formula, and produces a presumptively correct support amount. "Presumptively correct" means the court must order that amount unless a parent proves specific statutory reasons to deviate.

DissoMaster is not the only certified calculator. California also certifies CalSupport (and CalSupport Pro, by Nolotech), Family Law Software, and FamilySoft SupportCalc.

The Guideline Formula Behind the Number

Regardless of which software runs the calculation, every certified program applies the same Family Code Section 4055(a) formula:

CS = K × [HN − (H% × TN)]

• CS — the monthly child support order
• HN — the higher earner's net monthly disposable income
• TN — both parents' combined net monthly disposable income
• H% — the percentage of time the higher earner has physical custody
• K — a statutory fraction based on income bands and timeshare

Every single percentage point of physical custody time directly changes the output. A parent with 30% timeshare pays significantly more in support than a parent with 40% timeshare — which is why the parenting schedule and child support are never truly separate issues.

The Five Inputs That Drive Your Number

DissoMaster asks for dozens of data points, but five inputs have the largest impact on your support calculation:

1. Gross income from all sources — wages, bonuses, commissions, self-employment income, rental income, severance, military housing allowances, and non-need-based veterans' benefits all count. The court casts a wide net.

2. Mandatory deductions — federal and state income taxes, FICA, mandatory union dues, health insurance premiums you actually pay, and any child or spousal support paid in other cases. These reduce your net disposable income.

3. Physical custody timeshare percentage — calculated as the proportion of annual hours (out of 8,760) each parent has primary physical responsibility for the children. DissoMaster converts your parenting schedule into this percentage automatically.

4. Number of children — the guideline amount scales with a multi-child multiplier: 1.6x for two children, 2.0x for three, 2.3x for four.

5. Tax filing status — whether you file as single, head of household, or married filing separately changes your effective tax rate, which changes your net disposable income, which changes your support obligation.

SB 343: What Changed in 2024

Senate Bill 343, effective September 1, 2024, made the most significant overhaul to California's child support system in decades. The changes are baked into all currently certified software:

Re-banded K-factor tables — the lowest income band, frozen for years at $0–$800, was updated. The new bands start at $0–$2,900 and better reflect modern cost of living.

Minimum wage-based low-income adjustment — the LIA threshold is now tied to the California minimum wage ($16.90/hour in 2026), producing a threshold of approximately $2,929 per month. Any obligor earning below this threshold is presumptively entitled to a downward adjustment.

Proportional add-on split — before SB 343, mandatory add-ons (childcare costs and uninsured medical expenses) were split 50/50 regardless of income disparity. Now they must be divided proportionally based on each parent's adjusted net disposable income.

The DCSS Decertification

In March 2026, the public California Child Support Guideline Calculator (the free DCSS portal) was officially decertified by the Judicial Council. A customized version still operates inside the internal case management system used by Title IV-D child support commissioners, but the public-facing tool is no longer certified for private family law filings.

For self-represented parents, this means you cannot rely on the old free public calculator. Your options are:

• Ask your attorney or mediator to run the calculation using their licensed software
• Purchase a certified program — CalSupport and CalSupport Pro are the most affordable options
• Request the CCRC counselor or Family Court Services run the calculation during your mediation session

What DissoMaster Cannot Tell You

The calculator produces a number, but it cannot tell you whether your inputs are correct. The most common errors that skew results:

• Underreporting income (especially self-employment, stock options, or RSU vesting schedules)
• Using an incorrect timeshare percentage because the parenting schedule is vaguely written
• Forgetting to include mandatory add-ons (childcare and medical expenses) as separate line items
• Entering the wrong tax filing status

If your co-parent is self-employed, owns a business, or has complex compensation, a forensic accountant may be necessary to verify the income figures before they go into the calculator.

The California Child Custody & Parenting Plan Guide includes a child support input worksheet that walks you through every data point DissoMaster needs — so your calculation reflects your actual financial situation, not a rough estimate.

See more California guides →