Worked example · updated 2026-08-02

California, one child, and what forty per cent of the overnights is worth

A hypothetical California household run twice through Family Code section 4055: once with a substantially shared schedule and once with alternate weekends. Everything else is held constant, so the difference between the two figures is the timeshare term and nothing else.

Illustrative worked example. The household is hypothetical; every figure is computed by the same verified engines and rule packs the calculators use.

The situation

In this hypothetical California household there is one child before the court. The higher earner has net monthly disposable income of $7,500; the other parent has $4,000. The child spends a substantial but unequal share of the year's overnights with the higher earner. The same household is then computed again with an alternate-weekend schedule and no other change, so the two results can be compared directly. Every figure is produced by the section 4055 engine against the verified California pack.

What goes in

Children before the court: 1
Higher earner’s net monthly disposable income: $7,500
Other parent’s net monthly disposable income: $4,000
Annual overnights with the higher earner: 146

What comes out

Guideline monthly child support

$935

Family Code §4055 evaluated on the net disposable figures entered.

Timeshare the formula usesOvernights divided by the days in a year, as the statute frames it.: 40%
Combined net monthly disposable income: $11,500
Same household at alternate-weekend contactFifty-two overnights a year instead, everything else unchanged.: $1,543
What the extra overnights are worth each month: $608

Verified 2026-08-02 against California Family Code §4055 (statewide uniform guideline), added by Stats. 2023, Ch. 213, Sec. 3 (SB 343), operative September 1, 2024 (effective 2024-09-01)

The statute is algebra, and the timeshare sits inside it

California does not look support up in a table. Section 4055 states it as an equation: the support amount equals a factor the statute calls K, multiplied by the higher earner's net disposable income less the timeshare share of the parents' combined net disposable income. Because the timeshare term appears inside the equation rather than as an adjustment bolted on afterwards, every overnight moves the result. There is no threshold to cross and no step to fall on the wrong side of — which is the opposite of how most income-shares states handle parenting time.

K is not a constant, and that is where calculators go wrong

The statute derives K from a bracket table keyed to combined net disposable income, and every bracket expresses K in terms of the timeshare percentage. For most brackets the term is one plus the timeshare; for two of them the statute inverts it. So the timeshare enters the calculation twice, and a program that scales the main equation while holding K fixed will understate the order — badly, at shared-parenting levels. That is not a hypothetical failure. It is the defect our own verification pass against the state's calculator caught in this engine, and the reason the two brackets with an inverse term forced a change to the data shape as well as to the code.

The comparison is the point

Running the same household at alternate weekends and reading the difference is more informative than either figure alone. It answers a question people actually have — what is another night a fortnight worth — with arithmetic rather than assertion, and it does so in the one state where the answer is continuous rather than a cliff. It also shows the limit of the exercise: the difference is what the formula does with a schedule, not what a court will order, and a parenting schedule is decided on the child's interests rather than on a support figure.

What this engine deliberately does not do

California's own calculator carries a full tax engine and derives net disposable income from gross pay. Ours does not. It starts from the net figures entered and applies section 4055 to them, which makes every step legible and checkable but puts the responsibility for establishing the input somewhere else. That is why the state's calculator is linked prominently on the California page rather than buried: it is the right place to settle the input, and this is the right place to see what the statute does with it. There is also a discretionary low-income adjustment that the statute frames as a range; the engine reports that it may apply and applies nothing, because the choice belongs to the court.

What this example is good for

It gives a defensible starting figure and, more usefully, a measured answer to what a change in the parenting schedule does to it in the one state whose formula responds continuously. Both are inputs to a conversation, not a prediction of an order.

Run this with your own numbers — Child Support

Every state sets child support with a published guideline formula — income shares, percentage of income, or the Melson formula. Pick your state to run its own math step by step, see which figures the statute actually uses, and open the official worksheet it comes from.

Calculators behind this example

Child Support

Custody Planner

Build a parenting schedule from the standard rotations courts see most — 2-2-3, 2-2-5-5, 3-4-4-3, week-on-week-off, or every other weekend — then count the overnights exactly. The percentage carries straight into your state’s child support calculator, and the calendar exports and prints.

Estimate only — not legal advice. This is the published math for child support calculator by state, shown as a range. Your actual outcome depends on facts, evidence, and decisions this page cannot see.

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🗓️California, one child, and what forty per cent of the overnights is worth