“[In D.B.S.] Bastarache J. also discusses how a court should assess and award the correct amount of retroactive support, including the date from which it will be payable and the quantum. He concludes that the fairest retroactive date is the date when “effective notice” was given by the recipient spouse to the payor spouse that child support needed to be renegotiated. He stated that all that is required for effective notice is that the subject be broached. However, if after broaching the subject, the recipient parent does not pursue the matter, the payor parent may again begin to rely on the status quo. For that reason, Bastarache J. concluded that it will usually be inappropriate to select a date more than three years prior to the formal notice of the claim.
However, the date of retroactivity can be extended back in time for a payor parent who withholds information about a material change in circumstances, such as income increases that would entitle the child to increased support. In those circumstances, the presumptive date will be the date of the material change, as “[a] payor parent cannot use his/her informational advantage to justify his/her deficient child support payments” (para. 124).
Bastarache J. concludes as follows (at para. 125):
The proper approach [for determining the date of retroactivity] can therefore be summarized in the following way: payor parents will have their interest in certainty protected only up to the point when that interest becomes unreasonable. In the majority of circumstances, that interest will be reasonable up to the point when the recipient parent broaches the subject, up to three years in the past. However, in order to avoid having the presumptive date of retroactivity set prior to the date of effective notice, the payor parent must act responsibly: (s)he must disclose the material change in circumstances to the recipient parent. Where the payor parent does not do so, and thus engages in blameworthy behaviour, I see no reason to continue to protect his/her interest in certainty beyond the date when circumstances changed materially. A payor parent should not be permitted to profit from his/her wrongdoing.”