“S. (D.B.) v. G. (S.R.), 2006 SCC 37 (“DBS”), is the leading case on “retroactive” child support – the enforceability and quantification of support that was neither paid nor claimed when it was supposedly due.
The court noted, at para. 2, that such “retroactive” awards are not truly retroactive:
They do not hold parents to a legal standard that did not exist at the relevant time. But they are “retroactive” in the sense that they are not being made on a go-forward basis: the parents who owe support (the “payor parents”) are being ordered to pay what, in hindsight, should have been paid before.
Beginning at para. 80 of DBS, the court discussed the awarding of retroactive child support in the absence of an existing court order for child support, the situation in the present case. The court noted that “absent special circumstances (e.g., hardship or ad hoc sharing of expenses with the custodial parent), it becomes unreasonable for the non-custodial parent to believe he was acquitting himself of his obligations toward his children. The non-custodial parent’s interest in certainty is generally not a very compelling one”. At para. 83, the court in DBS appropriately referred to such orders as “retroactive original orders.””