*727OPINION
MATTHEWS, Justice.Under review in this case is an order that increased the child support that David H. Potter must pay and modified his visitation privileges. We conclude that the order is sustainable as to child support but not as to visitation because no notice was given that the latter issue was to be tried.
David Potter and Shelly Brewster divorced in 1990. The decree incorporated a custody and support agreement which nominally gave Brewster primary physical custody of the parties' daughter, Sunny, but included a detailed visitation order that essentially allowed the parties to have shared physical custody. Potter was to pay child support of $532 per month. Over the nine years that followed, the parties largely ignored the details of the visitation order but amicably shared custody and visitation. During much of this period, Sunny regularly stayed in Potter's home and may have spent as much time with him as with Brewster. But eventually Sunny began to spend less time with Potter and more with Brewster. By 1999, when she was fourteen years old, Sunny evidently lived full-time with Brewster and visited Potter only occasionally.
In May 1999 Brewster filed a pro se motion to increase child support payments, alleging that Sunny lived primarily with her. Potter, pro se, opposed the motion, essentially claiming that he had paid almost all of Sunny's expenses to date and had shared equally in her custody. The superior court scheduled an evidentiary hearing on the motion to increase child support for January 27, 2000.
By then both parties had hired attorneys. A week before the hearing Brewster's counsel filed two pleadings. The first was a motion to modify visitation and child support. The second was a motion to hold the first in abeyance. Brewster explained in a pleading filed January 27, 2000, that these motions were filed only as part of
a contingency plan. In the event Mr. Potter prevails and the court will not increase child support without modification of visitation ... Ms. Brewster will have in place, with an early filing date, an alternative method. Ms. Brewster does not really want to instigate a custody modification proceeding with the requisite best interests inquiry which would necessarily involve input from her 14-year-old daughter. Above all she wants to protect Sunny from involvement in litigation. Ms. Brewster believes that she is working on behalf of Sunny by seeking child support from her father which is both fair and necessary and if support can be modified without modifying the custody order, as is our position here, she will withdraw this secondary motion.
On January 27 the court decided to take testimony from Brewster but otherwise continue the scheduled hearing. The court described the issues and proceedings of that date in an order of February 18, 2000, as follows:
By the January 27 hearing, it was clear that there were a number of factual disputes regarding the incomes of the parties and the amount of time Sunny had been spending with each parent. It was also clear that counsel had not had sufficient time to investigate and prepare for an evidentiary hearing on all of these issues and that the issues concerning income were likely to be resolved by the parties if they had additional time to exchange doeu-ments. There were also a number of related issues in dispute. The most significant legal issues were (1) whether the court should decide child support on the basis of a sole custody calculation or a shared custody calculation and (2) whether the number of overnights allowed under the parties' settlement agreement or the actual number of overnights Sunny spent with Potter should control his child support obligation. The court agreed to hear testimony from Brewster since she and her counsel had traveled to Homer for the hearing, but to continue the hearing to allow the parties additional time to prepare. The court also agreed to address the legal issues described above before the next hearing. The court permitted counsel to supplement their briefing on the legal issues.
*728On February 23 the evidentiary hearing continued. At the outset, so that the issues to be tried would be "confined," Brewster's counsel sought a ruling that child support could be changed without modifying the visitation order. The superior court so ruled. The parties then proceeded to try the child support issue, understanding that the court had ruled that the parties' actual visitation practices would determine how child support would be calculated. After the February 28 evidentiary hearing the parties submitted final arguments in writing, both focusing entirely on issues of child support.
Several months after the parties submitted their final arguments, the superior court issued its written decision. The court changed child support from $532 to $997 per month. The court calculated child support under Civil Rule 90.8(a), relating to primary physical custody, rather than Civil Rule 90.3(b), relating to shared physical custody. The court also modified visitation, ruling that Potter would have "reasonable visitation" that was "to be determined by the parties with a focus on rebuilding the relationship between Sunny and Potter, and without concern for child support ramifications."
From this decision Potter appeals, making the following contentions:
1. That modifying visitation violated due process because he had no notice that visitation was at issue.
2. That modifying visitation was erroneous because there was no substantial change in circumstances.
8. That child support must be based on decreed visitation rather than the visitation practices of the parties.
4. That certain factual findings concerning visitation are clearly erroneous.
Brewster responds to these arguments as follows:
1. That due process was not violated because her contingent motion to modify the child custody agreement put visitation at issue and the court did not rule on her companion motion to hold the motion in abeyance.
2. That the parties' practices regarding visitation justified the change in visitation.
3. That the child support modification can be upheld based on the parties' actual visitation practices, even if it was error to modify visitation.
We agree with Potter that he was not given notice that modification of visitation would be at issue in the evidentiary proceedings and therefore the court's order regarding visitation does not satisfy due process. This conclusion moots his second argument. But we agree with Brewster that child support was properly modified prospectively based on the parties' visitation practices. Finally, we do not believe that the court's challenged findings of fact regarding visitation are clearly erroneous.
Our conclusion that the court erred in modifying the visitation decree without giving the parties notice that this was an issue for trial follows from the pretrial proceedings. Brewster argued that child support could be changed based on the parties' past practices with respect to visitation without changing the visitation decree. She wanted to avoid a trial regarding visitation modification because she believed that such a trial would involve the testimony of Sunny and she did not want Sunny to be involved. Potter, on the other hand, contended that child support must be based on decreed visitation and argued that if Brewster wanted increased support she would have to prosecute her motion to modify visitation. The superi- or court, wishing to avoid the "potential problem of Sunny getting involved in this whole dispute, as a player," agreed with Brewster and confined the issues as Brewster requested.
Due process under the Alaska Constitution requires, at a minimum, that parties be notified of the subject of proceedings concerning them so that they will have a reasonable opportunity to be heard.1 Here this requirement was not met. Potter was given no notice that modification of decreed visitation was at issue-indeed, based on the court's rulings, both parties reasonably ex*729pected that decreed visitation would not be at issue. Potter's due process rights were therefore violated.
We turn next to the question whether prospective child support can be modified based on the parties' actual, as distinct from decreed, visitation practices without also modifying the underlying visitation decree.
As noted, Potter argues that child support awards must be based on the visitation decreed in a governing order rather than the actual visitation practices of the parties. He cites the following language from Turinsky v. Long:
Child support awards should be based on a custody and visitation order. If the parties do not follow the custody order, they should ask the court to enforee the custody order or should move to modify the child support order.... We hold that the trial court erred to the extent it based its caleu-lation of support arrearages on the visitation exercised, rather than the visitation ordered.[2]
Potter also quotes another case, Bennett v. Bennett,3 that explains the rationale underlying Turinsky as follows:
We established this principle to prevent parents from interfering with court-ordered custody and visitation in order to gain an increase in child support payments. We intended as well to encourage parents to either comply with court orders or to move to modify them in a timely manner.[4]
Brewster responds that Potter is overgeneralizing from the quoted language in the Turinsky and Bennett cases. She points out that those cases both involved claims for past child support rather than, as here, an order setting child support prospectively. Brewster contends that applicable precedent is found in Boone v. Boone5 and in the commentary to Civil Rule 90.3, section V, paragraph C.6 In Boone, Brewster argues, this court held that a change in a child's residence from one parent to the other, contrary to a custody order, could serve as the basis for modifying child support.7 She points out that the support was changed prospectively after a motion to modify child support was made.8 This was accomplished even though the custody order was not modified during the same period.9
Custody and visitation, on the one hand, and child support, on the other, are interrelated under Civil Rule 90.3. Ordinarily, when parties informally agree to make a change in decreed custody or visitation that is not merely temporary or experimental, the change should be reflected both in a changed custody or visitation order and in a changed child support order. As we stated in Morino v. Swayman:
[AJt some point, informal or de facto modifications of custodial or visitation arrangements should be formalized. Child support amounts and the number of visitation days allotted to the non-custodial parent are interdependent under Civil Rule 90.3(a) and (b). A premise of the rule is that it is in the best interests of the children that child support amounts bear a prescribed relationship to the time the children spend with each parent. But this *730can only be accomplished where the decree reflects actual practice. Thus, justice is best served if the child support amount reflects the actual responsibilities and burdens of the parties.[10]
We believe that it is generally desirable to base prospective child support awards on prospectively applicable custody or visitation awards. But we agree with the commentary, and with Brewster's interpretation of Boone, that child support can be modified in recognition of a de facto change in visitation or custody without the de facto visitation or custodial change being formalized.11 There may be reasons of expediency justifying litigating child support before taking up issues of visitation or custody.12 Further, setting child support is in large part a predictive function. How much income will a parent make in the next year or two? The court must sometimes make what is little more than an educated guess based on the available evidence.13 And what has happened in the past is usually a strong component of the available evidence.14 Similarly, another component of child support, the amount of visitation a parent will exercise in the future, is also a prediction that can be based on past practices. By contrast, decreed visitation is ideal based-what is best for the child, and the parents? The best visitation practices may be worth retaining in a decree in the hope that they will occur, even if they are not consistent with what is likely to occur. Recognition of the difference between what should occur and what will probably occur seems to underlie the commentary's statement that support may be modified even if custody is not.
The commentary also stresses that its rule must not be used in a way that allows a custodial parent to profit by denying visitation.15 We agree and because of this risk and the various direct and indirect ways that visitation can be denied and discouraged we caution that only rarely should child support be set in an amount that reflects visitation practices different from decreed levels.
We conclude that the court did not err when it modified child support based on the parties' actual visitation practices and the child support modification can stand even though the modification of visitation must be reversed. |
Potter's final point is that the superior court erred in finding that the amount of time that Sunny has spent with Potter has decreased over the past few years and that Sunny has lived primarily with Brewster and has spent less than thirty percent of her time with Potter during that period. Findings of fact such as these must be upheld unless they are clearly erroneous.16 The findings in question are not clearly erroncous because they are supported by Brewster's testimony. Although her testimony on these points is contested by Potter, it is not inherently incredible.
Potter also argues that the court erred by "apparently" relying on visitation practices subsequent to Brewster's motion to modify child support. Potter is correct that post-litigation events should either be discounted entirely or viewed with suspicion as evidence of the parties' practices.17 But here there is little to indicate that the court relied on post-litigation events and virtually nothing shows that they played an important role in the court's findings. We therefore find no error on this point.
We conclude for the reasons stated that the court's decision must be vacated insofar as it modified the 1990 decree as to visitation, but that it should be affirmed as to child support.
*731AFFIRMED in part and VACATED in part.
FABE, Chief Justice, with whom CARPENETI, Justice, joins, dissenting.. See, e.g., D.M. v. State, Div. of Family & Youth Servs., 995 P.2d 205, 212-14 (Alaska 2000).
2. 910 P.2d 590, 595 (Alaska 1996).
. 6 P.3d 724 (Alaska 2000).
4. Id. at 727.
. 960 P.2d 579 (Alaska 1998).
. Section V, paragraph C of the commentary states:
Failure to Exercise Shared Custody. An inequity may arise under the shared custody calculation of support if the obligor does not actually exercise the custody necessary to make shared custody applicable (Le., at least 30% of the time). If the obligor parent does not actually exercise sufficient physical custody to qualify for the shared custody calculation in the rule (at least 110 overnights per year-See Commentary, Section V.A), then (a)(2) of this rule will apply to the child support calculation. Failure to exercise custody in this regard is grounds for modification of support, even if the custody order is not modified. However, this provision may not be interpreted to allow the custodial parent to profit by denying visitation.
. 960 P.2d at 582.
. Id.
. Id.
10. 970 P.2d 426, 429 (Alaska 1999).
. See Alaska R. Civ. P. 90.3 cmt. V.C.
. Id.
. See Yerrington v. Yerrington, 933 P.2d 555, 557-58 (Alaska 1997).
. See Alaska R. Civ. P. 90.3 cmt. III.E.
. See Alaska R. Civ. P. 90.3 cmt. V.C.
. Alaska R. Civ. P. 52(a).
. See, e.g., Karpuleon v. Karpuleon, 881 P.2d 318, 321-322 (Alaska 1994).