Jeffrey Cody, Appellant, vs. Tollefson Development, Inc., Respondent.

 STATE OF MINNESOTA
 IN COURT OF APPEALS
 C4-99-936

In Re the Marriage of:
Susan Ann Spaeth, petitioner,
Appellant,

vs.

Bradley Andrew Spaeth,
Respondent.

 Filed November 23, 1999
Reversed and remanded
Harten, Judge

St. Louis County District Court
File No. F1-92-100185

Richard E. Prebich, Lara Whiteside, Law Offices of Richard E. Prebich, 1932 Second Avenue East, Suite 2, Hibbing, MN 55746 (for appellant)

Andrew J. Phillips, Phillips Law Office, 412 First Street South, Virginia, MN 55792 (for respondent)

Considered and decided by Kalitowski, Presiding Judge, Amundson, Judge, and Harten, Judge.

 U N P U B L I S H E D   O P I N I O N

 HARTEN, Judge

Appellant Susan Ann Spaeth challenges the district court's denial of her motion for a money judgment against respondent Bradley Andrew Spaeth for unpaid child support. Because the district court erroneously found that appellant waived her right to claim child support arrearages, we reverse and remand.

 FACTS

In 1989, the district court dissolved the marriage of appellant and respondent pursuant to a stipulated judgment that determined, among other things, child support and custody. The parties agreed to joint legal custody of their two children, with appellant to have sole physical custody. The parties also agreed that respondent would pay appellant 30% of his income for child support. Respondent provided appellant with his paycheck stubs and child support payments until March 1992, when appellant assigned her right of collection to the St. Louis County Child Support and Collection Division (County). Respondent was thereafter required to provide his paycheck stubs with his payments to the County for verification of correct payment, and he did so.

On January 26, 1998, an administrative law judge ordered modification of child support. The modification order increased respondent's child support obligation and changed the payments from a percentage of his income to a fixed monthly amount. Respondent continued to make his payments to County.

On January 4, 1999, appellant moved to compel respondent to provide her with copies of his federal and state tax returns for the years 1992 through 1997, exclusive of 1996, in order for her to determine if there were child support arrearages owing. On January 15, 1999, appellant's motion was granted.

On March 3, 1999, appellant moved for a money judgment seeking alleged child support arrearages from respondent. By order dated May 7, 1999, the district court denied appellant's motion, finding that (1) the parties had agreed that respondent would pay appellant 30% of his income for child support, and would provide paycheck stubs as confirmation; (2) in March 1992, appellant had assigned her right to collection to the County and respondent was to send the County his stubs and payments; (3) at all times respondent complied with these requirements; (4) at no time did appellant or the County notify respondent that he was not complying with the requirements of the 1989 judgment or that his payments were insufficient; and (5) because appellant and the County accepted each paycheck stub and child support payment, they waived any claim that respondent's payments were insufficient.

Appellant asserts that the district court erred in finding that she waived her right to arrearages. Appellant argues that (1) equitable defenses do not apply to child support arrearages; (2) waiver of child support violates public policy; and (3) she could not have waived arrearages that she did not know existed until she brought her motion.

 D E C I S I O N

Findings of fact shall not be set aside unless clearly erroneous. Minn. R. Civ. P. 52.01. "[T]his court will only reverse a trial court's findings of fact if, upon review of the entire evidence, we are `left with the definite and firm conviction that a mistake has been made.'" In re Guardianship of Dawson, 502 N.W.2d 65, 68 (Minn. App. 1993) (quoting Gjovik v. Strope, 401 N.W.2d 664, 667 (Minn. 1987)), review denied (Minn. Aug. 16, 1993).

The district court found that appellant and County waived any right to bring an action for child support arrearages by accepting respondent's paycheck stubs and child support payments.[1]

 1. Laches

Respondent asserts laches as a defense, arguing that appellant is now claiming child support arrearages for many years during which respondent always provided the required information to appellant and County, who made no complaint. Laches is an equitable defense. See Minneapolis Public Housing Authority v. Lor, 591 N.W.2d 700, 703 n.13 (Minn. 1999) (laches as an equitable defense). Equitable defenses are inapplicable to child support arrearage motions. Stich v. Stich, 435 N.W.2d 848, 852 (Minn. App. 1989). See also Benedict v. Benedict, 361 N.W.2d 429, 432 (Minn. App. 1985) ("Equitable defenses are not available in an action for support arrearages brought within the statutory limitation period.").

 2. Waiver

Appellant next argues that she could not waive something unknown to her. Waiver is the voluntary, intentional relinquishment of a known right. Black's Law Dictionary 1580 (6th ed. 1990); Hedged Inv. Partners v. Norwest Bank, 578 N.W.2d 765, 771 (Minn. App. 1998). Voluntary choice is the essence of waiver. Cohler v. Smith, 280 Minn. 181, 189, 158 N.W.2d 574, 579 (1968). Waiver is largely a matter of intention and there can be no waiver without actual or implied intent to waive. Id. Accordingly, the waiver must be based on full knowledge of the facts. Id. Appellant claims she did not know that her assent to respondent's paycheck stubs and acceptance of his child support payments could constitute a waiver of arrearages. Appellant also claims she did not suspect arrearages existed until recently because she did not know that respondent's actual income differed from what was reflected in his paycheck stubs.[2] The district court made no findings of fact necessary to establish the elements of waiver.

Appellant also argues that waiver of child support violates public policy. Child support relates to the non-bargainable interests of children. Aumock v. Aumock, 410 N.W.2d 420, 421 (Minn. App. 1987). The child support guidelines reflect a legislative determination that children are entitled to benefit from the income of the noncustodial parent and to enjoy the standard of living that they would have had if the marriage had not been dissolved. Letourneau v. Letourneau, 350 N.W.2d 476, 478 (Minn. App. 1984). The parties recognize that respondent agreed to pay 30% of his income to appellant for child support. But appellant does not concede that by separate agreement between the parties the 30% excludes overtime and tax refunds. The district court made no findings of fact regarding a purported agreement on overtime and tax refunds.[3] Any agreement between parents waiving child support is not binding on the court, which must be guided primarily by a concern for the best interest of the child. Aumock, 410 N.W.2d at 421 (citing Tammen v. Tammen, 289 Minn. 28, 30, 182 N.W.2d 840, 842 (1970)).

We conclude that the district court erred in finding that appellant and the County waived the right to claim child support arrearages.[4] We therefore reverse the district court's order denying appellant's motion for civil money judgment. We remand for further findings on the issue of arrearages and direct the district court to determine what, if any, arrearages exist. On remand, the district court has discretion to reopen the record and take additional evidence on the issue of arrearages, including evidence concerning any agreement between the parties as to the inclusion of tax refunds and overtime in determining child support.

Reversed and remanded.

[1] As to the district court finding that the County waived any right to claim arrearages by accepting respondent's paycheck stubs and support payments, we note that an assignment of collection rights empowers a county to collect past and current support payments, but does not empower it to release unilaterally or discharge benefits decreed in a dissolution judgment. Stich v. Stich, 435 N.W.2d 848, 852 (Minn. App. 1989).

[2] The record indicates that respondent's paycheck stubs included his overtime hours and pay, but that the County did not include overtime when computing his child support obligation. There is no evidence that appellant knew the County was excluding overtime. Moreover, there is evidence that respondent's tax refunds were not included in computing his child support obligation.

[3] See Johnson v. Johnson, 533 N.W.2d 859, 863-64 (Minn. App. 1995) (holding that overtime is included in income for purposes of determining child support unless it began after entry of the existing support order); Koury v. Koury, 410 N.W.2d 31, 32-33 (Minn. App. 1987) (finding that income tax refund must be included in determining funds available for child support). But see McNattin v. McNattin, 450 N.W.2d 169, 171 (Minn. App. 1990) (finding that parties may modify child support in a stipulation and the court may consider the agreement in establishing child support since it represents the parties' acquiescence in a settlement); see generally Minn. Stat. § 518.551, subd. 5(b)(2) (1998) (addressing overtime income for child support purposes).

[4] The district court did not make a finding that no arrearages exist. If arrearages do exist, by finding a waiver the court functionally forgave the arrearages. Forgiveness of unpaid child support is a retroactive modification of child support governed by Minn. Stat. § 518.64, subd. 2. Darcy v. Darcy, 455 N.W.2d 518, 524-5 (Minn. App. 1990). A court may modify an order for support only on the motion of a party, and the court must make specific findings supporting the forgiveness of arrearages. Minn. Stat. 518.64, subds.1, 2 (1998).