In Re the Marriage of: Donald Baumgartner, petitioner, Appellant, vs. Ardeth Baumgartner, Respondent.

may not be cited except as provided by

Minn. Stat. § 480 A. 08, subd. 3 (1998).

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 C1-98-1502

In Re the Marriage of:

Donald Baumgartner, petitioner,

Appellant,

vs.

Ardeth Baumgartner,

Respondent.

 Filed January 26, 1999

 Affirmed as Modified

Davies, Judge

Otter Tail County District Court

File No. F0971236

Todd W. Foss, Stefanson, Landberg, and Plambeck, P.O. Box 1287, Moorhead, MN 56560 (for appellant)

Charles A. Krekelberg, Jeffrey D. Skonseng, Krekelberg Law Firm, 213 South Mill Street, Fergus Falls, MN 56537 (for respondent)

Considered and decided by Davies, Presiding Judge, Klaphake, Judge, and Amundson, Judge.

 U N P U B L I S H E D O P I N I O N

 DAVIES, Judge

Appellant contends the trial court erred in its determination and distribution of marital property and by not awarding respondent permanent maintenance in lieu of a marital property award. We affirm as modified.

 FACTS

The parties had been married 40 years at the time of the dissolution. Appellant Donald Baumgartner was, and continues to be, a farmer, while respondent Ardeth Baumgartner was a homemaker and the primary caregiver for the parties' four children.

Approximately a year before the marriage, appellant signed a contract for deed to buy the land known as the "homestead quarter" for $14,000. At trial he testified that the down payment was $1,600--$700 of which he paid out of his own funds at the time and $900 of which he borrowed from his sister and repaid during the marriage. He stated that, before the marriage, he also made an additional payment of $1,500--$800 against principal and $700 for interest. He also testified that he made improvements on the land before the marriage by fencing and remodeling the hog barn. Those improvements had to be substantially replaced, however, over the following 41 years.

The trial court found that the homestead quarter was primarily marital property, but gave appellant a credit of $3,389.50, primarily for what it calculated to be a nonmarital interest traceable to the $700 portion of the down payment paid from his own funds. The court found appellant had not persuasively demonstrated that he made the claimed second payment before the marriage; and it did not credit him with the improvements made on the land because the fences and the hog barn became marital property when they were substantially repaired and replaced during the marriage. Another section of land, referred to as the "north quarter," was purchased and paid for during the marriage, and the court determined that this was entirely marital property.

The trial court found that respondent had made a substantial contribution to the acquisition and preservation of the marital assets through her work as a housewife and homemaker. The court determined that a fair and equitable division of the marital property required that she be given one half of the marital assets. The court awarded respondent the north quarter and awarded appellant the homestead quarter, including the buildings on the homestead quarter and all the machinery and livestock. Because this resulted in an unequal distribution of assets, the court awarded a lien on the homestead in favor of respondent in the amount of $105,000. This appeal followed.

 D E C I S I O N

 I.

Although a reviewing court need not defer to a trial court's legal conclusion about the marital or nonmarital nature of property, we must, unless the findings are clearly erroneous, accept findings of fact made in support of those conclusions. Reynolds v. Reynolds, 498 N.W.2d 266, 270 (Minn. App. 1993). Appellant makes the following assertions with regard to the underlying facts: (1) the trial court erred by not finding that he had paid a larger portion of the homestead quarter down payment; (2) the trial court erred by failing to find a nonmarital interest arising from improvements to the homestead quarter made before the marriage; and (3) the trial court erred by making no findings with regard to his premarital interest in livestock.

 A. Percent of Purchase Price Paid with Nonmarital Funds

The trial court's failure to find that appellant had contributed a greater portion of the market value of the homestead quarter with nonmarital funds was not error. The trial court did not abuse its discretion with its finding that, before the marriage, appellant contributed only $700 toward the purchase price--five percent of the original $14,000. Appellant's own testimony was the only evidence he presented regarding his premarital payments. The trial court believed his statement that he contributed the initial $700, but did not credit his statement that he made an additional $800 payment before the marriage. A reviewing court must give due regard to the trial court's opportunity to judge the credibility of witnesses. Korf v. Korf, 553 N.W.2d 706, 712 (Minn. App. 1996). It was not clear error for the trial court to conclude that only one premarital payment was made.

The trial court did err, however, by valuing appellant's nonmarital interest at only $3,389.50. Applying the formula recognized by the Minnesota Supreme Court for calculating nonmarital and marital interests, his nonmarital interest was $6,500--the value of the land of the homestead quarter at the time of the divorce ($130,000) multiplied by five percent (the ratio of his premarital payment ($700) to the price of the property at the time of purchase ($14,000)). See Schmitz v. Schmitz, 309 N.W.2d 748, 750 (Minn. 1981) (nonmarital interest in house determined by multiplying value at time of separation by percentage of nonmarital property applied to original purchase price); see also Brown v. Brown, 316 N.W.2d 552, 553 (Minn. 1982) (reversing and remanding property distribution not made in accordance with Schmitz formula). The discrepancy between the trial court award and what appellant would have received under the formula is $3,110.50. That is a significant amount. We modify the judgment to give appellant a $3,110.50 credit by deducting that amount from the $105,000 lien granted in favor of respondent.

 B. Failure to Find Nonmarital Interest from Improvements

The trial court did not err by declining to attribute to appellant a nonmarital interest from improvements to the homestead quarter made before the marriage. The trial court found that appellant completed some fencing and repair on a hog barn before the marriage. It also found, however, that improvements made to the property after the marriage, including a new home, new barn, new cattle shed, new stock ponds, more fencing, and regular maintenance and repair, were primarily responsible for the increase in value. In light of these improvements made in the intervening 40 years, it found that appellant's premarital contribution was de minimis. These findings are not clearly erroneous, and the trial court did not err by not awarding appellant a premarital interest in improvements. See Nardini v. Nardini, 414 N.W.2d 184, 194-95 (Minn. 1987) (Schmitz formula not to be rigidly applied when property in question is complex combination of real and personal property and events of intervening years dilute significance of original nonmarital interest).

C. Lack of Findings Regarding Livestock

The lack of findings regarding the marital or nonmarital nature of appellant's livestock was not error. Property acquired during marriage is presumed to be marital. Minn. Stat. § 518.54, subd. 5 (1998). The party who asserts that an asset is nonmarital has the burden of proof. Wiegers v. Wiegers, 467 N.W.2d 342, 344 (Minn. App. 1991). Appellant did not raise this issue or present any evidence regarding it at trial. Appellant presented nothing to satisfy the tracing obligation with respect to the livestock. Appellant put forth no argument that evidence regarding the livestock could not have been presented at trial. The trial court did not err by denying appellant's motion to amend or for a new trial. See Minn. R. Civ. P. 52.02 (motion to amend made on the "files, exhibits, and minutes of the court," not on new evidence); Minn. R. Civ. P. 59.01(d) (grounds for new trial include "[m]aterial evidence newly discovered, which with reasonable diligence could not have been found and produced at the trial").

 II.

The division of marital property falls within the broad discretion of the trial court. Weikle v. Weikle, 403 N.W.2d 682, 686 (Minn. App. 1987), review denied (Minn. June 30, 1987). When dividing the parties' marital property, the court must consider the contribution of each party in its acquisition and preservation of the property, and it must be "conclusively presumed that each spouse made a substantial contribution to the acquisition of income and property while they were living together as husband and wife." Id. (quoting Minn. Stat. § 518.58 (1986)). The trial court did not err by determining that the parties had, over the course of their marriage, contributed equally to the acquisition of the marital property and did not abuse its discretion by dividing the marital assets equally between them. See id. (equal division of marital property is appropriate in cases involving dissolution of long-term marriage).

 III.

The trial court has broad discretion with regard to spousal maintenance determinations, and its decision to reserve the issue will not be reversed absent an abuse of that discretion. Wopata v. Wopata, 498 N.W.2d 478, 485 (Minn. App. 1993). In this case, it is uncontested that respondent has rheumatoid arthritis and is unable to perform substantial gainful employment. The court also found that, although she is able to meet her needs from the interest on assets awarded in the dissolution, her future income and expenses are uncertain; the court, therefore, reserved the issue of maintenance. This was not an abuse of discretion. See id. (reservation of maintenance appropriate when both parties currently self-sufficient, but one party's health is uncertain). See also Minn. Stat. § 518.55, subd. 1 (1998) (allowing court to reserve issue of maintenance for later date).

 Affirmed as modified.