Husband appeals the trial court’s denial of his request for retroactive modification of his child support obligation and claims the trial court erred in interpreting the terms of his obligation and in calculating arrearages.
FACTS
John (husband) and Delores (wife) Vellin-ga were divorced in 1981. At the divorce hearing, husband and his attorney1 offered a stipulation and agreement (stipulation) which was accepted by the trial court and incorporated by reference in the divorce decree.
Under the terms of the stipulation, wife was granted custody of the couple’s one child and husband agreed to pay child support. Husband was employed as a real estate salesman at the time of the divorce and has continued to be so employed. The stipulation required him to pay 15% of his gross earnings as child support. Husband was to make the support payments on or about the fifth day of each month following receipt of his commission check.
Husband fell behind in his support payments. He made no payments in 1986. When this pattern of non-payment continued until September 1987, wife filed an order to show cause, seeking arrearages. Wife requested that arrearages be based *473upon 15% of husband’s gross earnings from real estate commissions.
The hearing was held on October 26, 1987. Three days prior to the hearing husband filed a petition urging the trial court to either: 1) interpret the terms of the stipulation to mean that his support obligation was based upon his total income as reported in his income tax return, or 2) retroactively modify and recalculate his support obligation based upon either his income as taken from his tax returns or upon his commission income after subtracting his business expenses. Husband urged the trial court to adopt one of these alternative theories rather than base his support obligation on his gross income from real estate commissions.
The trial court ruled that husband’s support obligation was to be based upon his gross earnings from real estate commissions. The trial court found that husband’s gross earnings from real estate commissions totaled $226,939.25 for the period of time from 1981 through October 23, 1987. The trial court further found, by applying the 15% formula, that husband was obligated to pay $34,040.89 for the same period of time. From this amount the trial court subtracted the amount of child support that husband had paid, $11,202.50,2 to arrive at a finding of arrearages in the amount of $22,838.39. Judgment was entered accordingly.
ISSUE I
DID THE TRIAL COURT ERR IN DENYING HUSBAND’S REQUEST FOR MODIFICATION OF HIS PAST DUE SUPPORT PAYMENTS?
Husband contends that the trial court had the authority to retroactively modify his support obligation. Specifically, he claims that SDCL 25-7-7.3 only applies to payments which accrue after the effective date of the statute. He contends that the trial court erred in denying his request for retroactive modification of the payments which accrued prior to July 1, 1987.
Wife urges that the trial court properly denied husband’s request for retroactive modification. She asserts that SDCL 25-7-7.3 prohibits modification of arrearages which accrued prior to the time that the trial court was petitioned for modification.
Prior to passage of SDCL 25-7-7.3, this court held that a trial court had authority to retroactively modify child support payments. State ex rel. Larsgaard v. Larsgaard, 298 N.W.2d 381 (S.D.1980). Retroactive modification was permitted under the discretion provided by SDCL 25-4-41 and SDCL 25-4-45. Id. Modification was allowable even where the original judgment was based upon a stipulation between the parties. Connolly v. Connolly, 270 N.W.2d 44 (S.D.1978).
In 1987, however, the South Dakota Legislature addressed the issue of retroactive modification of past due support payments with the enactment of SDCL 25-7-7.3. That statute provides:
Any past due support payments are not subject to modification by a court or administrative entity of this state, except those accruing in any period in which there is pending a petition for modification of the support obligation, but only from the date that notice of hearing of the petition has been given to the obli-gee, the obligor, and any other parties having an interest in such matters.
The question of whether SDCL 25-7-7.3 is to be given retroactive application is an issue of first impression for this court. The construction of a statute is a question of law. Nash Finch Co. v. South Dakota Dept. of Rev., 312 N.W.2d 470 (S.D.1981). Rules regarding the construction of statutes have, however, been set forth by the South Dakota Legislature. Statutes are not to be construed as retroactive unless such intention plainly appears. SDCL 2-14-21. Words are to be under*474stood in their ordinary sense. SDCL 2-14-1.
The express language of SDCL 25-7-7.3 divides past due support payments into two groups: 1) payments which accrue subsequent to the petitioning for modification, and 2) payments which accrued prior to the petitioning for modification. Payments which accrue while a petition for modification is pending may be modified, but only from the date that notice of hearing has been given to the obligee and any other interested parties. Payments which accrued prior to the filing of a petition to modify may not be modified.
The legislature’s intent to prohibit modification in all but very limited circumstances plainly appears on the face of the statute. A narrow window is provided for modification of past due payments which accrue after notice of hearing is given to the obligee. Any other past due support payments are not subject to modification. The use of the term any, understood in its ordinary sense, clearly encompasses both past due support payments which accrued after the effective date of the statute and those which accrued prior to July 1, 1987.
In applying the rules of statutory construction to SDCL 25-7-7.3, we conclude that legislature’s intention that this statute be given retroactive application plainly appears on the face of the statute. We further note that in 1987 the legislature enacted several additional statutes that address child support obligations. See SDCL 25-7-7.1 through SDCL 25-7-7.5. For the most part, the purpose of these statutes appears to be to clarify and generally tighten the liability of the obligor. This comprehensive effort by the legislature further persuades the court that SDCL 25-7-7.3 was intended to be given retroactive application. Each statute must be construed according to its manifest intent as derived from the statute as a whole, as well as other enactments relating to the same subject. Meyerink v. Northwestern Public Service Co., 391 N.W.2d 180 (S.D.1986). For these reasons, we specifically hold that SDCL 25-7-7.3 is to be applied retroactively.
Husband did not petition the court for modification of past due support until October 23, 1987, three days before the hearing was held. The payments which he sought modification of accrued prior to the filing of his petition. SDCL 25-7-7.3 prohibits modification of payments which accrued prior to the filing of a petition for modification. The trial court properly refused to modify husband’s past due support obligation. We affirm the trial court on this issue.
ISSUE II
IN INTERPRETING THE TERMS OF HUSBAND’S SUPPORT OBLIGATION AND IN CALCULATING ARREARAG-ES, DID THE TRIAL COURT ERR IN REFUSING TO CONSTRUE GROSS EARNINGS TO MEAN TOTAL INCOME AS TAKEN FROM HIS INCOME TAX RETURNS?
The stipulation that the parties entered into at the time of the divorce, provides that:
7. a. The parties acknowledge that Plaintiff’s [husband’s] earnings are derived from real estate commission sales, and because of the unpredictability of his earnings, the parties agree that Plaintiff shall pay to Defendant as child support, 15% of his gross earnings which are to be paid on or about the 5th day of each month following receipt of his commission check, if any.
Husband argues that the term gross earnings was intended to mean the total income shown by his income tax returns. In the alternative, husband argues that gross earnings should be construed to mean his net income from his real estate commissions. Under this alternative theory gross earnings would be arrived at by subtracting his business expenses from his gross income from real estate commissions. In support of this alternative theory, husband argues that at the time of the divorce his business expenses were paid by the broker with whom he was associated. After the divorce, commencing sometime in 1981, he was required to pay his own expenses. Husband claims that the trial *475court erred in not interpreting gross earnings according to one of his theories.
Husband’s alternative theories of interpretation were presented for the trial court’s consideration. The trial court was unpersuaded. The trial court noted from the bench that husband had “made his own deal” and that determining the amount he owed is “just a matter of running a calculator.”
The trial court specifically found that husband proposed the stipulation and knew and understood its meaning. The court further found that the stipulation required husband to pay 15% of his total gross earnings from his real estate commissions each month as child support. Specific findings were entered regarding the amount of husband’s gross earnings from real estate commissions, the amount of child support paid since the divorce, and the amount of back support due to wife. The trial court concluded that wife was entitled to these arrearages as a matter of law and entered judgment accordingly.
The trial court did not find the terms of the stipulation which imposed the support obligation to be ambiguous. Neither do we. Interpreting gross earnings to mean the gross income from husband’s real estate commissions is no more than a literal reading of the express language of the agreement. The trial court did not err in interpreting the terms of the stipulation.
' The trial court is affirmed on the merits of this issue as well. Only the recalculation of the amount of arrearages is remanded to the circuit court in order that the addition error, as explained in footnote 2, may be corrected.
MORGAN, SABERS and MILLER, JJ., concur. HENDERSON, J., dissents. McMURCHIE, Circuit Judge, for WUEST, C.J., disqualified.. Neither party is represented by the attorney that represented him or her in the original divorce proceedings.
. Upon review this court notes that there appears to be an error in the addition of the support payments actually made. The amounts of paid support listed on page 4 of wife's brief and on page 18 of the settled record total $12,-202.50 rather than $11,202.50. If the amount of support payments actually made is in error, the amount of arrearages due will be in error by the same amount.