[¶ 1] We are asked to calculate the ten-day period for a motion to reconsider under N.D.R.Civ.P. 59(j), and to decide if social security dependency payments should be credited against a child-support arrearage. We affirm, concluding the motion under N.D.R.Civ.P. 59(j) was timely, and no credit for the dependency payments was appropriate.
I
[¶ 2] Brenda Lee Austin (formerly known as Brenda Lee Glatt) and Anthony Towne (formerly known as Anthony Glatt) divorced in 1981. The district court awarded Austin custody of their two minor children, and awarded Towne visitation and ordered him to pay $100-per-month child support. In 1989, Towne began receiving disability benefits from the Social Security Administration for a period beginning in 1986. The children received dependency benefits directly from the Social Security Administration.
[¶ 3] Between 1981 and 1991, Towne accumulated substantial child-support arrearage.
[¶ 4] In 1991, under a written stipulation for amended judgment, the district court suspended Towne’s parental rights and temporarily suspended his responsibilities, including payment of child support. He had over $7,000 in child-support arrearage at that time.
[¶ 5] In 1995, Towne requested a hearing to discuss modifying the arrearage. The district court found, under N.D.C.C. § 14-08.1-05(l)(e), child-support arrearage could not be retroactively modified and denied Towne’s motion on December 14, 1995. On May 24, 1996, the district court issued an income withholding order requiring the Social Security Administration to withhold $100 per month from Towne’s income. Towne filed a motion to reconsider modification of his child-support arrearage. On July 16, 1996, the district court denied the motion.
[¶ 6] Towne appeals the denial of his motion to reconsider under N.D.R.Civ.P. 59(j). The district court had jurisdiction under N.D.C.C. § 27-05-66. The appeal is timely under N.D.R.App.P. 4(a). This Court has jurisdiction under N.D. Const. Art. VI, § 6, and N.D.C.C. § 28-27-01.
II
[¶7] A motion to reconsider is a motion to alter or amend the judgment under N.D.R.Civ.P. 59(j) “for purposes of tolling the time period for filing [a] notice of appeal.” Continental Cas. Co. v. Kinsey, 499 N.W.2d 574, 582 (N.D.1993); see also Ellingson v. Knudson, 498 N.W.2d 814, 817 n. 5 (N.D.1993) (“Motions to reconsider are like motions to amend or alter judgments under Rule 59(j), N.D.R.Civ.P,”). Although Towne moved to reconsider the “JUDGEMENT (sic) entered in this action on July 16, 1996,” the document of that date is not a judgment but rather a memorandum opinion and order. Because the memorandum opinion and order was clearly intended to be final, we treat it as a final judgment. See American Ins. Co. v. Midwest Motor Express, 554 N.W.2d 182, 183 n. 1 (N.D.1996) (memorandum decisions are generally not appealable unless the memorandum decision “demonstrates it was intended to constitute the final order of the court”).
[¶ 8] A decision on a N.D.R.Civ.P. 59 motion is within the sound discretion of the trial court. Lapp v. Reeder Pub. Sch. Dist. No. S, 544 N.W.2d 164, 166 (N.D.1996); Schatke v. Schatke, 520 N.W.2d 833, 835 (N.D.1994). We will not reverse the denial of a motion under N.D.R.Civ.P. 59 absent a manifest abuse of discretion. Lapp; Schatke. “A trial court, abuses its discretion if it acts in an-arbitrary, capricious, or unreasonable manner, or if it misinterprets or misapplies the law.” Filler v. Bragg, 1997 N.D. 24, ¶ 9, 559 N.W.2d 225; Weber v. Weber, 548 N.W.2d 781, 783 (N.D.1996).
III
[¶ 9] A trial court does not abuse'its discretion by denying a N.D.R.Civ.P. 59(j) *898motion if the motion was not timely. See Brakke v. Brakke, 525 N.W.2d 687, 690 (N.D.1994) (it is an abuse of discretion when a trial court denies a timely filed motion as untimely). Austin argues the motion was not timely because it was not made within ten days of the memorandum opinion and order.
[¶ 10] Under N.D.R.Civ.P. 59(j), “[a] motion to alter or amend the judgment must be served not later than ten days after notice of entry of the judgment.” The issue is not whether the motion was made within ten days of entry of judgment, but whether it was made within ten days of notice of entry. N.D.R.Civ.P. 59(j).
[¶ 11] In this case, there is no “notice of entry of judgment” contained in the record. However, the ten-day time limit for filing a motion to reconsider under N.D.R.Civ.P. 59(j) will also begin to run when the defendant has “actual knowledge of entry of [an] order ... clearly evidenced in the record.” Lang v. Bank of North Dakota, 377 N.W.2d 575, 576 (N.D.1985).
[¶ 12] The record contains a sworn affidavit of mailing stating copies of the district court’s finding and order of December 14, 1995, were mailed to Towne on January 16, 1996. We have recognized, however, “[a]n affidavit of mailing may be record notice but it does not equate with actual notice under these precedents establishing an exception to the requirement of service of notice of entry of judgment.” Thorson v. Thorson, 541 N.W.2d 692, 694-95 (N.D.1996). Therefore, the affidavit of mailing does not show Towne had actual knowledge of the district court’s order of December 14, 1995.
[¶ 13] The first clear evidence in the record showing Towne had actual knowledge of entry of the order is his June 17, 1996, “Motion to Vacate [the] Order of 1991 of Child Support and Visitation Termination,” in which Towne requested “credit for child support by the way of Social Security Disability payments.” Towne’s ten-day period under N.D.R.Civ.P. 59® thus began on June 17, 1996. He moved to reconsider on June 24, 1996, well within the permissible ten days.
IV
[¶ 14] Because a district court abuses its discretion if it misinterprets or misapplies the law, denial of Towne’s motion would be an abuse of discretion if Towne were legally entitled to a credit against his child-support arrearage for the social security dependency payments to his children. Towne relies on our decision in Guthmiller v. Guthmiller, 448 N.W.2d 643 (N.D.1989). We recently interpreted Guthmiller in Mehl v. Mehl:
“In Guthmiller ... we concluded social security dependency payments ‘made directly to [the] children or for their benefit’ presumptively constitute a change of circumstances for which the obligor is entitled to a credit toward his support obligation. The trial court’s decision in Guth-miller was rendered before the effective date of the 1989 amendments to Chapter 14-09, N.D.C.C., making the scheduled child support under the guidelines the presumptively correct support obligation. Under the current guidelines it may or may not be appropriate to credit social security dependency payments toward the obligor’s support obligation. See Stultz v. Stultz, 659 N.E.2d 125 (Ind.1995). Assuming the credit is appropriate, an issue we do not decide, the credit cannot be applied retroactively toward arrearage: ‘To apply the credit to the arrearage which accrued prior to the obligor’s filing of the modification application would amount to a retroactive modification' of vested support rights. This we will not do. The credit should be applied at the time of the filing, however, only if the benefits are then being paid to the dependent child or the child’s representative payee.’ ”
Mehl v. Mehl, 545 N.W.2d 777, 780-81 (N.D.1996). Past due and unpaid support cannot be retroactively modified. Throndset v. L.L.S., 485 N.W.2d 775, 780 (N.D.1992).
[¶ 15] In this case, Towne accumulated ar-rearage from 1981 to 1991. The children received Social Security Administration de*899pendency benefits in 1989. Towne did not apply for credit when the children began receiving benefits. Social Security Administration payments could not be credited retroactively to modify Towne’s arrearage.1 Because Towne was not entitled to have his child-support arrearage reduced by the social security dependency payments to his children, the district court did not abuse its discretion in denying Towne’s motion to reconsider under N.D.R.Civ.P. 59(j).
V
[¶ 16] The order of the district court is affirmed.
[¶ 17] VANDE WALLE, C.J., concurs.. This is essentially a pre-child-support-guide-lines case. Effective January 1995, amendments to N.D. Admin. Code §§ 75-02-04.1-01 and 75-02-04.1-02 relate to “children's benefits.” This opinion neither applies nor construes those provisions.