“This court in Gray (v. Rizzi, 2016 ONCA 152) clarified the approach to be followed when the threshold for a retroactive variation of support had been met. Specifically, at paras. 44- 54, the court made it abundantly clear that the four factors governing retroactive support orders identified in D.B.S., subject to exceptional circumstances, should be adapted to apply to applications to decrease support retroactively in cases like the present:
i. Whether there was a reasonable excuse as to why a variation in support was not sought earlier;
ii. The conduct of the payor parent;
iii. The circumstances of the child and;
iv. Any hardship occasioned by a retroactive award.
Gray rejected the notion that D.B.S. and its factors for analysis are inapplicable in cases of arrears, at para. 51:
[A] payor who has let arrears accumulate has no claim to resist an increase in support on grounds of certainty and predictability. A delinquent payor cannot use the principle of predictability as a shield against paying the full amount of support to which his child is entitled.
…
In contrast, where a payor seeks a retroactive decrease in support, the S. (D.B.) factors — such as taking into account the circumstances of the child, the conduct of the payor parent, the hardship of a retroactive award, and the reason for delaying in seeking a variation in support — remain relevant. [Emphasis added.]
At paras. 45 and 61-62, the court also endorsed the general rules from D.B.S. that the date of effective notice should serve as the date to which the award should be retroactive and that it usually will be inappropriate to make a support award retroactive to a date more than three years before formal notice was given (“the three-year rule”). While D.B.S. framed these rules in the context of giving certainty and predictability to the payor parent when the change is an increase sought by the recipient parent, Gray clarified that the same underlying principles apply when the change is sought by the payor parent: see D.B.S., at para. 123; Gray, at para. 61.”