What is the test for retroactive child support awards?

In Miglin v. Miglin, at paragraphs 131 – 135, Bastarache J. outlined some of the significant considerations relating to child support: 131 Child support has long been recognized as a crucial obligation that parents owe to their children. 132 In the context of retroactive support, this means that a parent will not have fulfilled his/her obligation to his/her children if (s)he does not increase child support payments when his/her income increases significantly…Once parents are in front of a court with jurisdiction over their dispute, that court will generally have the power to order a retroactive award that enforces the unfulfilled obligations that have accrued over time. 133 …The payor parent’s interest in certainty must be balanced with the need for fairness and for flexibility. In doing so, a court should consider whether the recipient parent has supplied a reasonable excuse for his/her delay, the conduct of the payor parent, the circumstances of the child, and the hardship the retroactive award might entail. 134 Once a court decides to make a retroactive award, it should generally make the award retroactive to the date when effective notice was given to the payor parent. But where the payor parent engaged in blameworthy conduct, the date when circumstances changed materially will be the presumptive start date of the award. It will then remain for the court to determine the quantum of the retroactive award consistent with the statutory scheme under which it is operating. 135 The question of retroactive child support awards is a challenging one because it only arises when at least one parent has paid insufficient attention to the payments his/her child was owed. …Thus, while retroactive child support awards should be available to help correct these situations when they occur, the true responsibility of parents is to ensure that the situation never reaches a pointwhen a retroactive award is needed.