When the §4055 guideline isn't the answer: §4057 deviation, in plain English

If you read our walk-through of the §4055 guideline formula or our explainer on the §4058 income definition, you might have come away thinking the number that pops out the end of CS = K × [HN − H%·TN] × multiChildMultiplier is the number. It usually is. But not always.

California Family Code §4057 is the statute that holds the door open. It says the §4055 guideline amount is presumed correct, and then it lists the specific circumstances under which a court can deviate from it. The presumption is rebuttable. It is not, however, easy to rebut. Family courts deviate from the guideline a lot less often than people assume they do, and the procedural requirements for doing so are strict in a way that catches both pro se litigants and the occasional attorney off guard.

This post is the §4057 walk-through. What the presumption actually means; what triggers a deviation; what §4056 requires the court to do on the record before it deviates; and a worked example showing what a deviation looks like in dollars.

§4057(a): the presumption

Verbatim from the statute:

The amount of child support established by the formula provided in subdivision (a) of Section 4055 is presumed to be the correct amount of child support to be ordered.

Two operative words. Presumed means the §4055 number is what the court starts with, every time, every case. Correct means it is the right number unless the moving party rebuts the presumption with the specific evidence §4057(b) describes.

A presumption is not a floor and not a ceiling. The presumption can be rebutted in either direction, upward (the court orders more than guideline) or downward (the court orders less). What §4057 controls is the evidentiary path to either of those outcomes.

The presumption is also more durable than people often expect. Appellate courts call the §4055 formula “rigid” and “algebraic” (In re Marriage of Hall (2000) 81 Cal.App.4th 313) and “presumptively correct” (In re Marriage of Cryer (2011) 198 Cal.App.4th 1039). Hall reversed an order that departed from guideline without the required §4056 statements. Cryer shows the other side: a deviation upheld because the trial court found special circumstances and explained them. SB 343 changed the K-table numbers; it did not change that doctrine.

§4057(b): the deviation triggers

Section (b) enumerates the situations in which the §4055 presumption is rebutted. The rebuttal has to be shown by admissible evidence, by a preponderance, and the court has to put the §4056(a) information on the record. Since SB 343 (operative September 1, 2024) there are six operative paragraphs:

§4057(b)(1): Stipulation. The parents agree to a different amount than guideline under §4065(a). This is the most common deviation path. Both parties have to agree, and under §4065(a) a below-guideline stipulation is approved only if the parties declare they are fully informed of their rights, aren’t agreeing under duress, the agreement is in the children’s best interests, the children’s needs will be adequately met, and support hasn’t been assigned to the county (no pending public-assistance application). With those guardrails, courts honor stipulated deviations routinely.

§4057(b)(2): Deferred sale of the family residence. When the sale of the family home is deferred (under §3800 et seq.) so the children can stay in it, the court can adjust support when the home’s rental value exceeds the mortgage, homeowner’s insurance, and property taxes, and the adjustment can’t exceed that excess. This paragraph mostly matters in higher-asset cases.

§4057(b)(3): Extraordinarily high income. The paying parent has an extraordinarily high income and the formula amount would exceed the children’s needs. More on this one below.

§4057(b)(4): Not contributing in line with custodial time. A party is not contributing to the children’s needs at a level that matches that party’s custodial time.

§4057(b)(5): Low-income obligor over 50%. If the obligor qualifies for the low-income adjustment under §4055(b)(7) and guideline support still exceeds 50% of their net disposable income after the adjustment, the court can reduce support, but only by the amount over 50%.

§4057(b)(6): Special circumstances. Application of the formula would be unjust or inappropriate due to special circumstances in the particular case. This is the catch-all. It exists to cover cases the legislature couldn’t itemize in advance, and its list of examples is expressly non-exhaustive (“include, but are not limited to”). Courts still read it narrowly: “special circumstances” has to be genuinely unusual, not just “this case is harder than I expected.” The statute names four:

• (A) Different time-sharing for different children. One child with one parent most of the time, another child with the other parent most of the time. The formula itself now averages the high earner’s timeshare across the children (§4055(b)(1)(D)), and (b)(6)(A) lets the court deviate if even that doesn’t fit.
• (B) Equal time-sharing with a housing-cost gap. Both parents have substantially equal time-sharing, and one parent spends a much lower or higher percentage of income on housing than the other.
• (C) Special medical or other needs. The children have special medical or other needs that could require child support greater than the formula amount. The classic example of an upward deviation.
• (D) More than two parents. A child is found to have more than two parents.

Travel expenses for visitation aren’t a §4057 deviation ground; they’re a discretionary add-on under §4062(b)(2).

If your case doesn’t fit (b)(1) through (b)(5) or a genuinely special circumstance under (b)(6), the court isn’t authorized to deviate. Even a court that thinks the guideline number is too high or too low cannot simply override it. The deviation has to ride on one of the §4057(b) grounds, supported by evidence.

§4056: what the court has to do on the record

§4057(b) is the substantive deviation rule. §4056 is the procedural one, and it is the part that most often catches litigants off guard.

When the court deviates from the guideline, §4056(a) requires it to state in writing or on the record:

1. The amount the §4055 guideline would have produced;
2. The reasons the §4055 amount would be unjust or inappropriate in this case;
3. The reasons the deviated amount is consistent with the best interests of the children.

When the court adopts the guideline (no deviation), §4056(b) still requires it to state, on request:

1. The net monthly disposable income of each parent;
2. The actual federal income-tax filing status of each parent;
3. The deductions from gross income for each parent;
4. The approximate percentage of time each parent has primary physical responsibility for the children compared to the other parent.

The §4056(b) findings are what your worksheet PDF supports: it is exactly the input set §4056(b) requires the court to recite. The §4056(a) findings, which the court must make to deviate, are what your attorney drafts and the judge signs.

Failing to make §4056 findings is generally reversible error. Courts of appeal have sent deviations back even where the number might have been defensible, because the §4055 figure and the reasons weren’t on the record (In re Marriage of Hall). This is the procedural trap.

A worked example: when special needs justifies an upward deviation

Two parents, two children, one with a documented special-needs profile. Real fact pattern, sanitized:

• Parent A: net disposable income $8,000/month, 25% custody timeshare.
• Parent B: net disposable income $4,000/month, 75% custody (primary).
• Combined TN = $12,000.
• §4062(a)(2) uninsured medical costs documented at $250/month average across both kids.
• The special-needs child has an additional $1,200/month of documented therapy, equipment, and specialist costs the family pays out of pocket, costs that exceed “reasonable uninsured health care costs” the §4062(a)(2) add-on captures.

The §4055 guideline math, run through our calculator on the current post-SB-343 K-table, lands at:

• Income fraction at TN = $12,000 → in the $10,001–$15,000 band → 0.10 + 1,499/12,000 ≈ 0.2249.
• Timeshare multiplier for H% = 0.25 → 1.25.
• Multi-child multiplier for 2 children → 1.6.
• K = 1.25 × 0.2249 ≈ 0.2811.
• CS = K × (HN − H%·TN) × multiChildMult = 0.2811 × ($8,000 − 0.25 × $12,000) × 1.6 = 0.2811 × $5,000 × 1.6 = about $2,249/month.

Parent A’s presumptive obligation under §4055 is $2,249/month in this fact pattern (the engine confirms it to the dollar). That is the number §4057(a) presumes correct.

Parent B moves under §4057(b)(6)(C) for an upward deviation of $400/month to fund the special-needs child’s documented out-of-pocket costs. The motion attaches receipts, therapist invoices, and an IEP. Parent A opposes on the ground that §4062(a)(2) already accounts for uninsured medical and that the deviation double-counts.

One aside before the ruling: before reaching for §4057, check whether the cost fits as a discretionary add-on under §4062(b)(1) (educational or other special needs of the children); that’s often the cleaner path. This example follows the deviation route because that’s what this post is about.

The court grants the deviation in part. It finds:

1. The guideline amount under §4055 is $2,249/month.
2. The §4055 amount is unjust in this case because $250/month of routine §4062(a)(2) medical does not capture an additional $1,200/month of special-needs costs the children’s best interest requires be funded. The §4055 formula, as written, does not account for special-needs care above and beyond uninsured medical.
3. A deviated amount of $2,649/month ($400 over guideline) is consistent with §4053(e) (children’s interests are the state’s top priority) and §4053(b) (both parents are mutually responsible for supporting their children).

That is a §4056(a)-compliant deviation order. $400/month above guideline is checked as a non-guideline order on the FL-342, with the findings on FL-342(A). The fact pattern would not support a $1,200/month full-cost-shift deviation (courts construe §4057(b)(6)(C) narrowly), but it does support funding a meaningful share of the documented additional costs.

If Parent B had moved without the §4062 framing, without acknowledging that some of the medical costs are already accounted for in the guideline, the court could have denied the motion as duplicative. The §4057 motion has to thread the needle between “the guideline is the right starting point” (it always is) and “but this fact pattern needs more than the guideline gives” (the burden of proof is on the moving party).

What §4057 is not

§4057 is not a hardship clause for the obligor. Hardship is governed by §§4070–4073, and it has its own framework: enumerated hardships under §4071 (extraordinary health expenses, uninsured catastrophic losses, support for other children living in the home), a cap on the other-children deduction under §4071(b), and a separate findings requirement under §4072. §4057 deviation and §4070 hardship can coexist in the same order, but they are distinct procedural tracks.

§4057 is not how you contest income or custody. If the dispute is about what the obligor’s income actually is, or what the timeshare percentage actually is, those are §4055-input disputes: the court reruns the formula with corrected inputs and arrives at a corrected presumptive figure. §4057 doesn’t come into play until the inputs are settled.

§4057 is not an easy exit from the guideline in expensive cases. Courts sometimes deviate under §4057(b)(3), which covers an extraordinarily high-income payer whose guideline amount would exceed the children’s needs. But the threshold is high: the formula has to overshoot the children’s actual needs, not just produce a big number. (Related: In re Marriage of Williams (2007) 150 Cal.App.4th 1221 held a court can’t impute income to a wealthy parent’s home equity without a §4057(b) special-circumstances showing.)

How to model deviation in our calculator

Our calculator computes the §4055 presumed-correct number: the figure §4057(a) presumes correct. It does not compute the deviation itself (deviation is a discretionary judicial finding, not arithmetic). What the calculator does do is:

• Show the §4055 figure clearly, so you can see what §4057(a) presumes correct in your case.
• Show the breakdown of K-factor, timeshare multiplier, multi-child multiplier, and the [HN − H%·TN] term, so any §4057(b)(6) special-circumstances argument can point at which piece of the formula it’s reacting to.
• Allow per-parent §4058(b) imputation modeling, so you can compare the guideline at “actual” inputs versus “imputed” inputs side-by-side, useful when the §4057 motion is really a §4058(b) earning-capacity argument in disguise.
• Print a worksheet PDF formatted as the FL-342 Item 1 computer-calculation attachment, with the §4055 + §4059 + §4062 + LIA + §4057 framing clearly broken out, so a court considering deviation has the inputs and the formula in front of it.

If the case ends up at a §4057 deviation motion, the workflow we suggest is: run the calculator to lock the guideline figure; print the worksheet; have a licensed California family-law attorney draft the §4057(b) motion citing the worksheet’s guideline number and arguing the specific §4057(b) ground.

What this post is not

This is a walk-through of §4057 and the §4056 procedural framework. It is not legal advice. The choice of whether to seek a deviation from the §4055 guideline in your case, and which §4057(b) ground to argue, is a strategic decision that benefits from a licensed California family-law attorney’s input. §4057 motions get denied as often as they get granted, and a poorly-framed motion can damage credibility on subsequent issues in the same case.

The two related pieces worth reading alongside this one: the §4055 K-table changes under SB 343 (because the deviation argument depends on what the guideline figure actually is), and the §4058 income definition (because most §4057 disputes are actually §4058-input disputes in disguise).

The statute text quoted above was current as of the statute_as_of date in this post’s frontmatter; we re-verify all citations quarterly. The page footer’s disclaimer applies to every section above.