In Re the Marriage of: Dean Richard Hanson, petitioner, Respondent, vs. Charon Katherine Tierney, Appellant.

may not be cited except as provided by

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

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 C4-99-32

In Re the Marriage of:

Dean Richard Hanson, petitioner,

Respondent,

vs.

Charon Katherine Tierney,

Appellant.

 Filed August 10, 1999

 Affirmed

 Parker, Judge[*]

Stearns County District Court

File No. F4954027

John Robinson Hill, Larkin, Hoffman, Daly & Lindgren, Ltd., 1500 Norwest Financial Center, 7900 Xerxes Avenue South, Bloomington, MN 55431-1194 (for respondent)

Lynne M. Ridgway, Hall & Byers, P.A., 1010 W. St. Germain Street, Suite 600, St. Cloud, MN 56301 (for appellant)

Considered and decided by Toussaint, Chief Judge, Halbrooks, Judge and Parker, Judge.

 U N P U B L I S H E D O P I N I O N

 PARKER, Judge

On appeal from the judgment dissolving the 17-year marriage of appellant Charon K. Tierney and respondent Dean R. Hanson, appellant challenges the (1) valuation of marital property; (2) award to respondent of a non-marital interest in the parties' homestead and business; (3) finding of respondent's income; and (4) the date child-support reimbursement begins. Respondent challenges the (1) business valuation; (2) retroactive application of medical-support obligations; and (3) ongoing medical-support obligation for the parties' child. We affirm.

 D E C I S I O N

1. After valuing the parties' property, the district court appropriately attempted to divide it equally. See Miller v. Miller, 352 N.W.2d 738, 742 (Minn. 1984) (equal property division presumptively equitable upon dissolution of a long-term marriage). The district court has broad discretion in valuing and dividing property. Maranda v. Maranda, 449 N.W.2d 158, 164 (Minn. 1989). Assigning a value to property is a finding of fact. Hertz v. Hertz, 304 Minn. 144, 145, 229 N.W.2d 42, 44 (1975). Findings of fact are not set aside unless clearly erroneous. Minn. R. Civ. P. 52.01. Appellate courts will not set aside a district court's division of property if the division has a reasonable basis in fact and principle. DuBois v. DuBois, 335 N.W.2d 503, 507 (Minn. 1983).

Appellant alleges the trial court overvalued her car by underestimating the amount by which it depreciated. In addressing the parties' disputes on this issue, the district court addressed the year, make, and model of the car, the date it was purchased, the parties' down payment, and the credit received for a trade-in. On this record, we cannot say appellant has shown that the district court clearly erred by overvaluing the car.

Respondent argues the district court overvalued the business awarded to him. District courts are not required to make a detailed analysis of the value of a business when dividing property, but the finding of a business's value will be set aside if it is not reasonably supported by the findings. Nemitz v. Nemitz, 376 N.W.2d 243, 246 (Minn. App. 1985), review denied (Minn. Dec. 30, 1985). Because the district court adopted the bulk of the business-valuation testimony of appellant's expert appraiser, and because there is no serious challenge to that expert's competency, we cannot say respondent has shown the district court's valuation of the business to be clearly erroneous. See Hertz, 304 Minn. at 145, 229 N.W.2d at 44 (stating property valuations will be affirmed if "within the limits of credible estimates made by competent witnesses even if it does not coincide exactly with the estimate of any one of them"). To the extent respondent challenges the portions of the expert's valuation that are based on use of a going-concern premium and a normal-life depreciation schedule, we note that (a) the business is a going concern; (b) various costs would be associated with organizing and starting a similar business; and (c) respondent has failed to argue persuasively how a depreciation schedule reflecting the actual life of the assets being depreciated can prejudice him. Similarly, to the extent respondent challenges the business valuation because it lacks the 15% marketability discount proposed by a neutral expert, we note that appellant's expert explicitly testified that such a discount was inappropriate here.

Noting respondent testified that he carried $800 cash at all times, appellant alleges the district court erred by not including $800 in respondent's property award. Because the district court considered the $800 as part of respondent's draw from the business (i.e., as part of his income) to simultaneously include that money in his property award would risk double-counting it. However, given the size of the parties' marital estate, we cannot say that an error resulting in a $400 benefit to appellant is sufficient to require a remand of the property division. See Wibbens v. Wibbens, 379 N.W.2d 225, 227 (Minn. App. 1985) (refusing to remand for minimal error); see also Minn. R. Civ. P. 61 (harmless error to be ignored).

2. Appellant challenges the awards to respondent of nonmarital interests in the homestead and business. Property acquired during a marriage is presumptively marital and a party seeking a non-marital interest must show, by a preponderance of the evidence, that the property in question is non-marital under Minn. Stat. § 518.54, subd. 5 (1998). Olsen v. Olsen, 562 N.W.2d 797, 800 (Minn. 1997). Whether property is marital or non-marital is a legal question subject to de novo review, but appellate courts defer to the district court's underlying findings of fact unless clearly erroneous. Burns v. Burns, 466 N.W.2d 421, 423 (Minn. App. 1991).

Based on respondent's testimony and supporting documentation, the district court found that respondent traced his non-marital interest in the business to premarital interests in a home and a prior business. The district court also found that respondent's non-marital homestead interest could be traced to the proceeds of his cabin, which were put into the checking account from which the down payment for the homestead was made eight days later. Having independently reviewed the record, we conclude there is adequate support for the district court's findings on these issues. Therefore, we affirm the rulings that respondent had a non-marital interest in the business and the homestead. See Wopata v. Wopata, 498 N.W.2d 478, 484 (Minn. App. 1993) (stating that for non-marital interest to be traceable, record must show "what ultimately happened" to funds "after they were received"); Kottke v. Kottke, 353 N.W.2d 633, 636 (Minn. App. 1984) (finding non-marital interest traceable when funds placed in joint checking account prior to purchase of homestead), review denied (Minn. Dec. 20, 1984).

3. It is undisputed that appellant's mother loaned the couple $15,000 and that the parties paid appellant's mother $200 per month for eight years thereafter. Appellant, alleging the monthly payments were for child-care and home-care services performed by her mother rather than debt repayment, challenges the district court's ruling that the debt was repaid. The question of whether debts have been repaid is reviewed under a clearly erroneous standard. Thomas v. Thomas, 356 N.W.2d 76, 79 (Minn. App. 1984). Here, because testimony conflicted regarding the debt repayment, the ultimate issue was one of witness credibility. Because the district court heard the testimony on this issue, we defer to the district court's reasonable determination that appellant's mother provided child care in return for room and board while living with the parties and that, hence, the monthly payments were made to repay the debt. See Sefkow v. Sefkow, 427 N.W.2d 203, 210 (Minn. 1988) (stating appellate courts defer to district court credibility determinations); see also Minn. R. Civ. P. 52.01 (requiring "due regard" to be given to district court's ability to judge witness credibility). We additionally note that because appellant did not call her mother to testify despite her mother's regular presence in the courtroom, the district court was justified in drawing inferences adverse to appellant on this issue. See Federated Mut. Ins. Co. v. Litchfield Precision Components, Inc., 456 N.W.2d 434, 436 (Minn. 1990) (stating unfavorable inferences may be drawn from party's failure to produce evidence in its possession); cf. Bollenbach v. Bollenbach, 285 Minn. 418, 428, 175 N.W.2d 148, 155 (1970) (stating party's failure to produce full account of debts and assets justifies adverse inferences).

4. Appellant challenges the finding of respondent's income. A finding of income for support purposes will be upheld if it has a reasonable basis in fact. Rouland v. Thorson, 542 N.W.2d 681, 685 (Minn. App. 1996). In finding respondent's income, the district court included the $337.13 after-tax value of the use of respondent's business vehicle, rather than its $426.75 pre-tax value. Appellant cites no authority showing this amount to be unreasonable. We note that even if the district court erred, any error is approximately $89 per month, which, considering respondent's net monthly income of $2,099, is a minimal amount. We decline to remand for any such minimal error. See Wibbens, 379 N.W.2d at 227 (refusing to remand for minimal error); see also Minn. R. Civ. P. 61 (harmless error to be ignored). Also, the district court did not err by allowing respondent a reasonable pension deduction of $134 per month, which is permitted under Minn. Stat. § 518.551, subd. 5(b) (1998).

Appellant also alleges the district court miscalculated respondent's income by omitting respondent's medical and life insurance premiums paid by respondent's business and by not including certain amounts paid by respondent's business on respondent's credit cards. Medical insurance premiums are a legitimate income deduction. Minn. Stat. § 518.551, subd. 5(b) (1998). Therefore, if they were included in respondent's income a commensurate deduction would also be included. Any error regarding the life insurance premiums paid by the business is $50 per month and minimal. Regarding the amounts paid by respondent's business on his credit cards, the district court heard testimony of both parties and decided to include in respondent's income a reasonable sum as in-kind income respondent received from the business. Also, respondent testified that he was repaying the business for various expenses it had paid on his behalf. The district court is in a better position than this court to determine the amounts to be attributed to respondent as income and to assess witness credibility. We defer to the district court's assessments. Sefkow, 427 N.W.2d at 210; see Minn. R. Civ. P. 52.01. To the extent appellant alleges the $800 cash respondent carries is from a source other than his monthly draw from the business, we note appellant neither cites the record nor authority to support her argument. See Minn. R. Civ. App. P. 128.02, subd. 1(c), 128.03 (requiring factual assertions to be supported by cites to record); Schoepke v. Alexander Smith & Sons Carpet Co., 290 Minn. 518, 519-20, 187 N.W.2d 133, 135 (1971) (assignment of error based on "their assertion" and unsupported by argument or authority is waived unless error is obvious). Appellant has not shown that the court clearly erred in calculating respondent's income.

5. The district court ordered respondent's child-support and child-care obligations to commence April 1, 1998. Appellant argues the obligations should have been retroactive to the commencement of these proceedings in 1995. A district court has broad discretion to set child support obligations and a support obligation will not be set aside unless it is an abuse of discretion. Korf v. Korf, 553 N.W.2d 706, 708 (Minn. App. 1996). Regarding child support, because the district court found that the difference between what respondent had voluntarily paid for child support and the amount he would have been ordered to pay for the same period was "insignificant," any failure to make the support obligation retroactive is minimal, if not harmless.

Despite the district court's finding that "[n]o evidence was provided to establish any past day care expenses," appellant now points to no record evidence addressing the day-care expenses she incurred while these proceedings were pending. Therefore, we affirm the district court's refusal to award back day-care expenses to appellant. See Taflin v. Taflin, 366 N.W.2d 315, 319 (Minn. App. 1985) (party cannot "complain" if failure to provide information leads to denial of request to reduce support). Because the judgment awards appellant $5,529.75 as half of the cost of the child's medical insurance during the pendency of these proceedings, the medical insurance provision is functionally retroactive to the beginning of the proceedings. Respondent was ordered to pay the medical and dental costs attributable to the child during the pendency of the proceeding. A district court may award retroactive child support. In re J.M.K., 507 N.W.2d 459, 461 (Minn. App. 1993); see Korf, 553 N.W.2d at 710 (Minn. App. 1996) (affirming trial court determination that support may be sought retroactively). Here, the court weighed each factor and came up with a reasonable back-support figure considering the fundamental duty of parents to support their children. The equitable powers of the court were reasonably exercised by allocating medical expenses during the proceeding to both parties. There was no abuse of discretion.

6. Apparently fearing a support obligation that may continue beyond the child's 18th birthday, respondent objects to the support-related portions of the judgment referring to his obligation to the parties' "child" rather than to the parties' "minor child." Due to the fact that the parties' child is diabetic, the condition of her health appears to indicate to respondent that he may be responsible for the child beyond minority. However, there is no current controversy that has been identified concerning the passages in the order of the court for medical support. We decline to issue an advisory opinion addressing the issue. See In re Schmidt, 443 N.W.2d 824, 826 (Minn. 1989) (stating court does not issue advisory opinions).

 Affirmed.

[*] Retired judge of the Minnesota Court of Appeals, serving by appointment pursuant to Minn. Const. art. VI, § 10.