How is interest calculated on unpaid child or spousal support arrears in Ontario?

This is an area where it's important not to assume the rules that apply to ordinary consumer debt automatically carry over to support arrears, because they don't necessarily work the same way. Whether and how interest applies to unpaid child or spousal support depends on the specific order or agreement in place and the enforcement framework being used, and this isn't something to treat as a fixed, universal percentage that applies to every case in Ontario.

Because the treatment of interest on arrears can vary depending on how the support obligation was created, whether it's being enforced through the Family Responsibility Office, and the specific terms involved, anyone trying to calculate exactly what's owed, including accumulated interest, should confirm the current approach directly with FRO or get advice from a family lawyer rather than relying on assumptions borrowed from other kinds of debt. This matters most for recipients trying to understand the true size of an arrears balance, and for payors trying to negotiate a realistic repayment plan, since an inaccurate assumption about interest can throw off both sides' expectations about what's actually owed and how quickly it grows.