State of Minnesota, Respondent, vs. David Kenneth Christian, Appellant.

may not be cited except as provided by

Minn. Stat. § 480 A. 08, subd. 3 (1996).

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 C2-97-1840

In re the Marriage of:

Debra Jean Schreur, petitioner,

Respondent,

vs.

Kevin James Schreur,

Appellant.

 Filed March 3, 1998

 Affirmed in part, reversed in part, and remanded.

 Lansing, Judge

Mille Lacs County District Court

File No. F997250

Richard W. Curott, Curott & Associates, 116 Second Avenue Southwest, Milaca, MN 56353 (for appellant)

Thomas J. Meinz, 515 First Street, Princeton, MN 55371 (for respondent)

Considered and decided by Lansing, Presiding Judge, Crippen, Judge, and Peterson, Judge.

 U N P U B L I S H E D O P I N I O N

 LANSING, Judge

In an appeal from judgment in a marital dissolution action, Kevin Schreur challenges the district court's calculation of Debra Schreur's net monthly income for support purposes and the calculation of the amount of support in light of the joint physical custody. The income calculation is supported by the record, but the parents' respective obligations indicate a departure without accompanying findings. We therefore affirm in part, reverse in part, and remand.

 FACTS

Kevin and Debra Schreur stipulated to joint physical custody of their two minor children and reserved certain issues, including child support, for determination by the court. The district court calculated each parent's income, set support amounts based on its understanding of the joint physical custody formula, and offset the parties' support obligations to each other.[1] Following denial of his motion to amend, Kevin Schreur appeals.

 D E C I S I O N

 I

The district court determined Debra Schreur's net monthly income based on 22.3 "guaranteed" weekly hours of work. Kevin Schreur claims this is erroneous because Debra Schreur admits working more than the guaranteed number of hours when additional work is available.

A finding of net income will not be set aside unless it is clearly erroneous. See Minn. R. Civ. P. 52.01 (findings of fact not set aside unless clearly erroneous); Kornberg v. Kornberg, 542 N.W.2d 379, 386 (Minn. 1996) (same); see also Strauch v. Strauch, 401 N.W.2d 444, 448 (Minn. App. 1987) (finding of net income for support purposes will be affirmed if it has a reasonable basis in fact). Debra Schreur acknowledges that she worked additional hours when they were available, but explained in her affidavit that her employer has informed her that "the recent hiring of additional staff will probably limit [her] ability to work extra hours."

The district court's exclusion of income that may be unavailable has a reasonable basis in fact. See Minn. Stat. § 518.54, subd. 6 (1996) (defining income, in part, as a "periodic payment"); Haasken v. Haasken, 396 N.W.2d 253, 261 (Minn. App. 1986) (stating, "[t]o properly be included in a calculation of net monthly income the payments need to be `the type of income which could or should provide a dependable source of child support'") (quoting Stangel v. Stangel, 366 N.W.2d 747, 749 (Minn. App. 1985)). Cf. Erler v. Erler, 390 N.W.2d 316, 319-320 (Minn. App. 1986) (holding trial court did not abuse its discretion by including income from "regular, steady" part-time employment as earnings for support purposes). To the extent Debra Schreur regularly works more than 22.3 hours per week, Kevin Schreur may move to modify support. See Minn. Stat. § 518.64 (Supp. 1997).

 II

When setting support, the district court has "broad discretion" and will not be reversed absent a clearly erroneous conclusion that is against logic and the facts on record. Moylan v. Moylan, 384 N.W.2d 859, 864 (Minn. 1986). When parties share joint physical custody of a child, the proper method of determining support is to apply the guidelines by requiring each parent to pay the guideline amount only during the months the other parent has custody. Hortis v. Hortis, 367 N.W.2d 633, 636 (Minn. App. 1985); see also Valento v. Valento, 385 N.W.2d 860, 862-63 (Minn. App. 1986) (Hortis method should be used in all joint custody determinations unless there are specific reasons for departure), review denied (Minn. June 30, 1986). The district court may deviate from the guidelines by making further findings "and may offset the respective child support obligations, annualize payments, or both, within its discretion." Hortis, 367 N.W.2d at 636.

The district court did not address the amount of time either parent acts as custodian of the children. Kevin Schreur claims the district court erred in setting support without considering what he claims is an equal split in the time each parent acts as custodian. The Hortis/Valento formula contemplates each parent paying support while the other parent has custody of the children. Hortis, 367 N.W.2d at 636; see Valento, 385 N.W.2d at 863 ("[a] party's support obligation is determined by his or her guideline amount for the period of time the other parent has custody") (emphasis added). Although the district court indicated that it set support based on the Hortis/Valento formula, its calculations were not computed using the period of time that each parent has custody but instead on the amount that each parent would pay if the other parent had physical custody of the children all the time. The court properly applied an offset, but the net result is an overstatement of Kevin Schreur's net monthly support obligation.

Debra Schreur defends the support award as an upward deviation from the guidelines and within the district court's discretion. But a deviation would require written findings justifying the deviation. Minn. Stat. § 518.551, subd. 5(i) (1996) ("court shall make written findings" to justify deviation); see Minn. Stat. § 645.44, subd. 16 (1996) ("`[s]hall' is mandatory"). Although we agree that Valento did not require such findings, the legislature amended the support guidelines after Valento was decided. See 1991 Minn. Laws ch. 292, art. 5, §§ 75-78 (amending child support guidelines).

The district court did not indicate that it intended to deviate from the guidelines, and it did not make the findings statutorily required for a deviation. Therefore, we remand for further determination of the support amount. See Erickson v. Erickson, 385 N.W.2d 301, 303 (Minn. 1986) (stating inadequate findings on modification issues requires remand). On remand, the district court should determine the amount of time each parent acts as custodian of the children and calculate a support obligation based on the Hortis/Valento formula. If the district court intends to deviate from the obligation calculated under the Hortis/Valento formula, the order should provide reasons for the deviation or for the choice of a differing formula. Whether to reopen the record on remand is discretionary with the district court.

  Affirmed in part, reversed in part, and remanded.

[1] A minor arithmetic error in the order caused Kevin Schreur's net monthly support obligation to be listed as $333.80 rather than $332.80.