concurring in part and dissenting in part:
I respectfully dissent. While I agree that this case presents an opportunity to establish helpful precedent, I disagree with the majority’s assessment of the record facts and the law that should apply to them.
This appeal grows out of a stipulated divorce decree. Two family court judges upheld the decree’s stipulation for joint physical custody. The only modification either judge made was to adjust the child’s residential timeshare arrangement slightly. After taking testimony from the parents, both of whom work, the second judge determined that the parents’ days off differed perfectly. Thus, each parent could have the child while the other was at work, minimizing the time the child had to spend in day care, if a one-day adjustment to the residential timeshare was made.
I do not find in the original stipulated decree the inflexible 5/2 timeshare the majority does. After providing for “joint legal custody and joint physical care, custody and control” of the parties’ daughter, the original decree provided for the father to have the child “each Sunday at 7 p.m. until Tuesday at 9:00 p.m. in addition to any time agreed on by the Parties.” (Emphasis added.) The residential timeshare, as adjusted, provided for the father to have the child from “Sunday at 1 p.m. until Wednesday at 2 p.m.” — thus adding a day to the father’s allotted two days and two hours per week but deleting the provision giving him such additional “time agreed on by the Parties” (who were having trouble agreeing to anything). The second family court judge made an express, on-the-record finding that, as adjusted, the residential timeshare arrangement was consistent with the stipulated decree’s provision for joint physical custody — and in the child’s best interest. The timeshare adjustment also obviated the mother’s argument that the court should not have approved the stipulated decree’s provision for a Wright-based offset, by which the parties had voluntarily agreed neither would pay child support to the other.
This strikes me as a sensible, maybe even Solomon-like solution. Instead of upholding the family court’s exercise of sound discretion, however, the majority reverses and remands these parents to the family court for more litigation. On remand, the family court is directed to establish the exact percentage of time the child has spent with *443each parent over the course of the past year;1 to then apply a newly announced 40-percent formula on which joint physical custody and future child support will depend; and thereafter to enter formal findings, beyond those stated in the decree and in open court, respecting these and other matters.
I submit that this result and the underlying formula the majority adopts are contrary to statute and case precedent. The family court interpreted its decree in a way that was fair, supported by the record, and consistent with applicable law. A sounder result would be to recognize the distinction other courts have drawn between true custody modification and residential timeshare adjustments and support the family court’s sound exercise of discretion as to the latter in this case.
DISCUSSION
The formulaic approach is inconsistent with Nevada law
I have a threshold concern with court-mandated formulas, in general, and with the 40-percent joint physical custody formula the majority adopts in this case, in particular, to determine child support and relocation disputes. A legislature has the capacity to debate social policy and to enact, amend, and repeal laws as experience and society dictate. Courts do not. The law courts apply is precedent-driven, or has its origin in statute or constitutional mandate. It is not only that judges tend to be innumerate, or that court-adopted formulas are of suspect provenance — though both are so — it is that laws adopted by judges are difficult to change if they do not work out. Because courts decide individual questions in individual cases, a bad rule of law can take a long time to return to a court; meanwhile, reliance interests counseling against changing that law are built. As the controversy over the original opinion and its withdrawal and replacement in this case suggest, establishing formulas is ordinarily best left to the Legislature.
More specifically troubling, the formulaic approach the majority adopts in this case is inconsistent with the approach the Nevada Legislature in fact chose to take. Thus, in 1987 the Nevada Legislature considered and rejected a proposal that would have established a 40-percent “joint physical custody” timeshare test and tied it to a corollary child support formula. A.B. 424, 64th Leg. (Nev. 1987), discussed in Barbagallo v. Barbagallo, 105 Nev. 546, 548, 779 P.2d *444532, 534 (1989). Instead of a mathematical formula, the 1987 Legislature adopted the multifactored approach to determining support found in today’s NRS 125B.080. Id. Based on this history, in 1989 this court held that it is “inappropriate for the courts to adopt their own formulas when the mathematical approach to adjusting the formula in joint custody cases has been considered and rejected by the legislature.” Barbagallo, 105 Nev. at 550 n.2, 779 P.2d at 535 n.2 (as amended by 786 P.2d 673 (1990)).
The point is not whether a formulaic approach is good policy, providing helpful bright-line rules; or bad policy, creating a hostile “on the clock” mentality inconsistent with truly cooperative joint parenting. On this, reasonable policymakers differ, as the foreign state statutes catalogued, ante at 424 n.5, 425 n.6, reflect. The point is that percentage time/support formulas are for the Legislature to evaluate, not for the court to establish by fiat.
The 40-percent joint physical custody test the majority adopts today, when tied, as intended, to eligibility for a child support offset under Wright v. Osburn, 114 Nev. 1367, 970 P.2d 1071 (1998), creates law indistinguishable from that Barbagallo says courts should abjure.2 As a near-contemporaneous judicial interpretation of a controlling statutory scheme, Barbagallo should control. See Neal v. United States, 516 U.S. 284, 294-95 (1996) (giving “great weight to stare decisis in the area of statutory construction” because the legislature “is free to change this Court’s interpretation of its legislation”; the Legislature, not the courts, “has the responsibility for revising its statutes”; and “[wjere we to alter our statutory interpretations from case to case, [the Legislature] would have less reason to exercise its responsibility to correct statutes that are thought to be unwise or unfair” (internal quotation omitted)).
The family court’s interpretation of its decree was sound
The stipulated decree was not irreconcilably inconsistent with joint physical custody
At its heart, this case asks how we should interpret the parties’ stipulated divorce decree. Historically, this court defers to a trial court’s interpretation of its own decrees. ‘ ‘It is the province of the *445trial court to construe its judgments and decrees.” Grenz v. Grenz, 78 Nev. 394, 401, 374 P.2d 891, 895 (1962). Further, “[w]here a judgment is susceptible of two interpretations, that one will be adopted which renders it the more reasonable, effective and conclusive, and which makes the judgment harmonize with the facts and law of the case and be such as ought to have been rendered.” Aseltine v. District Court, 57 Nev. 269, 273, 62 P.2d 701, 702 (1936) (internal quotation omitted).
Both family court judges acknowledged the tension between the stipulated decree’s joint physical custody provision and its original residential timeshare provision. They resolved the tension by giving priority to the parties’ overarching agreement to share joint legal and physical custody. The elasticity in the original timeshare provision, which gave the father such additional time “as agreed to by the Parties” beyond his specifically allotted time, makes this reading fair. It gives effect to all of the stipulated decree’s provisions, and it is consistent with the parties’ apparent intent and their frank, on-the-record admissions that neither believed the other was a bad parent, their dispute being mainly over money and scheduling.
The family court judges’ reading of the stipulated decree also comports with NRS 125.490, which states: “There is a presumption, affecting the burden of proof, that joint custody would be in the best interest of a minor child if the parents have agreed to an award of joint custody.” See NRS 125.480(1) and (3)(a) (stating preference for orders awarding joint custody and providing that “[i]f it appears to the court that joint custody would be in the best interest of the child, the court may grant custody to the parties jointly”; statement of reasons required only if joint custody denied). The parents here “agreed to an award of joint custody” and the family court judge specifically stated on the record that she found that the timeshare, as adjusted, was in the child’s best interest because it maximized the child’s time with each parent instead of at day care. Remanding for further findings regarding custody thus seems unnecessary.
The mother did not establish a basis to modify child support
Nor do I find a basis in the record to remand for further findings as to support. While not elaborate, the decree specified the applicable statutory percentage and stipulated that the parties were agreeing to a downward deviation and the basis therefor. It read:
The parties’ respective obligation of child support for the parties’ said minor child should are [sic] hereby offset and neither party is ordered to pay to the other child support; that this represents a deviation from the statutory child support formula as set forth in NRS 125B.070 (which states that child support for one child shall be eighteen percent (18%) of the non-custodial *446parent’s income), based on the parties’ joint legal and physical custody arrangement, pursuant to NRS 125B.080, subsection (9)(j). Each party shall jointly pay for the support and care of the parties’ minor child.
In addition, the stipulated decree obligated the father to pay for the child’s health insurance at a cost of $80 per month and to contribute $50 per month to an education fund for her, controlled by the child’s mother.
As the majority notes, the mother filed successive motions to modify support. In connection with the first motion to modify support, the court minutes reflect that the mother reaffirmed what was represented in the stipulated decree — that “the parties [stipulated to] share joint custody,” and that “the parties’ incomes are similar.” Both motions to modify relied on the alleged inconsistency between the agreement for joint physical custody and the timeshare provision. But read in conformity with the presumption in NRS 125.490, the stipulated decree was not irreconcilably inconsistent with joint physical custody. Further, any theoretical inconsistency was eliminated when the second judge modified the residential timeshare by substituting “Wednesday” for such additional time “as agreed on by the Parties,” establishing a 4/3 timeshare that falls within the majority’s 40-percent rule. Because neither of the underlying motions in this case identified a basis for modifying support besides the asserted lack of true joint physical custody timeshare agreement, further proceedings and findings, beyond those the original decree stated to justify its downward deviation, are unwarranted.3
Adjusting a residential timeshare in a joint physical custody arrangement is appropriate when in the child’s best interest
An agreement to share joint physical custody, interpreted in light of the child’s best interest, should determine the appropriate residential timeshare, not the reverse. Citing Wright, 114 Nev. at 1368, 970 P.2d at 1071-72, and Wesley v. Foster, 119 Nev. 110, 112-13, 65 P.3d 251, 252-53 (2003), the majority states that “[o]ur law presumes that joint physical custody approximates a 50/50 timeshare.” I do not read these cases as that definitive — much less as supporting the majority’s holding that a residential timeshare arrangement that works out to a child spending less than 40 percent of his or her time *447with one parent over the course of a year automatically invalidates a presumptively valid agreement for joint physical custody. As we recognized in Mosley, 113 Nev. at 54, 930 P.2d at 1112, a decree can validly establish joint physical custody even though the timeshare contemplated at the outset is not a 50/50 (or even a 60/40) arrangement, but one that will require fine-tuning over time.
Joint physical custody may ideally signify something approaching a 50/50 timeshare. However, I am concerned that our judicially mandated 40-percent formula will prove unsatisfactory, especially when used, as intended, to determine support and relocation disputes. Lives change and a child’s time is divided, not just between his or her parents, but among friends, school or day care, extended family, sports, and other pursuits. Practical questions seem certain to scuff the bright-line rule — questions like how to count hours the child spends with people besides either parent, or which parent to credit for time the child spends pursuing activities both parents support. Of greater concern, making child support, relocation, and custody determinations depend on parents keeping logs of the number of hours each year a child spends with one parent or the other (leaving aside the calculation and credit questions) detracts from the type of true co-parenting our statutes try to promote. See NRS 125.460; NRS 125.490; see also In re Marriage of Birnbaum, 260 Cal. Rptr. 210, 214-15 (Ct. App. 1989) (dismissing as a “popular misconception” the idea “that joint physical custody means the children spend exactly one-half their time with each parent”; noting that “[parents’ demands for equal amounts of a child’s time [can] constitute a disservice to the child”; and that, while “[i]n some cases the nature of the relationship between the parents may necessitate this kind of inflexibility[ u]sually it is temporary, and when the former spouses have adjusted to their new and limited relationship . . . mathematical exactitude of time is no longer necessary”); Rutter’s, California Practice Guide to Family Law § 7:358 (2009) (noting that “[a] joint custody order does not mean the child must equally split all of his or her time between the parents”); see also Mosley, 113 Nev. at 60, 930 P.2d at 1116 (noting that “NRS 125.460 dictates the public policy of this state in child custody matters [which is] that the best interests of children are served by frequent associations and a continuing relationship with both parents and by a sharing of parental rights and responsibilities of child rearing” (internal quotations omitted)).
*448This case invites us to distinguish between adjusting parents’ residential timeshare and formal proceedings to modify custody in the stipulated joint physical custody setting. California Family Code section 3011, like NRS 125.490(1), states a “presumption affecting the burden of proof” that agreements providing for joint custody are in a child’s best interest. Addressing joint physical custody agreements, several intermediate California courts have exhorted “parents [to] understand that successful joint physical custody depends upon the quality of the parenting relationship, not the allocation of time.” In re Marriage of Birnbaum, 260 Cal. Rptr. 210, 216 (Ct. App. 1989); see Enrique M. v. Angelina V., 18 Cal. Rptr. 3d 306, 313 (Ct. App. 2004).
Both Birnbaum and Enrique M. recognize that disputes over the details of residential timeshare arrangements in cases involving joint physical custody are best settled by the parents, not the courts. Enrique M., 18 Cal. Rptr. 3d at 314 (noting that such adjustments are ‘ ‘not on a par with a request to change physical custody from sole to joint custody, or vice versa”). Thus, they refuse to fuel these disputes by expanding them into full blown custody proceedings, or reviewing them on appeal as if that is what they involve. If the parents cannot agree on the child’s schedule, the family court should be held to “possess[ ] the broadest possible discretion in adjusting co-parenting residential arrangements involved in joint physical custody.” Birnbaum, 260 Cal. Rptr. at 216. This rule fosters the policy presuming joint custody to be in a child’s best interests and may even “obviate the need for costly and time-consuming litigation to change custody, which may itself be detrimental to the welfare of minor children because of the uncertainty, stress, and even ill will that such litigation tends to generate.” Enrique M., 18 Cal. Rptr. 3d at 313 (internal quotation omitted).
The dispute underlying this case is not identical to those presented in Birnbaum and Enrique M., since it concerned time spent in day care, and child support, not school choice and residence during the school year. But the underlying principle is similar: When parties have agreed to joint physical custody, absent a showing that some other arrangement is in the child’s best interest, courts should try to make that agreement succeed. In my estimation, we do the parties and their child a disservice by remanding this case for more litigation, instead of affirming the family court.
CONCLUSION
In sum, I would uphold the district court’s order as consistent with Nevada statutes that presumptively favor joint custody, especially agreed-upon joint custody, and require that before a joint custody decree is modified, it must be shown that the child’s best interest requires the modification. As district courts have broad discretion in deciding custody and support, so long as the policies *449set by statute are applied, the district court properly adjusted the parties’ timeshare agreement and declined to modify the child support obligation to which the parties agreed.
With the exception of the portion of the opinion affirming the order denying disqualification of the family court judge, therefore, I respectfully dissent.
The formulaic approach is especially problematic where, as here, the family court directs a highly specific timeshare. If the parties have abided by the timeshare directed, they will meet the court’s formula and joint physical custody will be established under the formula. If they haven’t, we will be incentivizing disregard of a court order and argument over whose fault the departure was. The family court’s approach seems preferable, in that it encourages self-determination by enforcing the parties’ agreed-upon decree and attempting to interpret it consistently with applicable law and the child’s best interest.
The majority justifies its adoption of a 40-percent test for joint physical custody as providing needed clarity in parental relocation as well as child support offset cases. Ante at 422, citing Potter v. Potter, 121 Nev. 613, 618, 119 P.3d 1246, 1249 (2005). Relocation is not an issue here because the stipulated decree provided that if either party moved away from Las Vegas, joint legal custody would continue but primary physical custody would shift to the mother, with liberal visitation, including foil summers, for the father. If anything, the decree’s relocation provision shows that the parties knew how to distinguish between joint and primary physical custody and meant what they said — an assumption that finds further support in the fact that each had experienced counsel in fashioning the stipulated decree.
In her reply in support of the motion to disqualify, the mother argued that the father had enjoyed an increase in income that independently justified modifying child support. While this would have been a proper basis to modify support, NRS 125B. 145(4), the family court could not consider it since this basis was not raised in either motion to modify, both of which predated the motion to disqualify and the reply in support thereof, where these arguments first emerged. Cf. Mosley v. Figliuzzi, 113 Nev. 51, 61, 930 P.2d 1110, 1116 (1997) (holding *447parties entitled to a written motion and advance notice of the alleged grounds before a custody modification order is entered). Now that the original decree is more than three years old, the mother is entitled to have its provisions respecting child support reviewed in any event, NRS 125B. 145(1), but that is not the basis for reversal and remand.