Last Updated: August 24 2026
How does the duty to mitigate losses work in an Ontario lawsuit if I believe the other party is causing the damages?
In Ontario, the duty to mitigate requires a person harmed by another party’s wrongful conduct to take reasonable steps to minimize their losses, and they generally cannot recover portions of damages that could reasonably have been avoided; the Supreme Court explained this in Southcott Estates Inc. v. Toronto Catholic District School Board, [2012] 2 S.C.R. 675 (paras. 23 to 25), and if a defendant argues failure to mitigate, it must plead the allegation in its defence and prove that mitigation was possible and the plaintiff had a reasonable opportunity to take such steps but the plaintiff does not need to mitigate perfectly, only reasonably at the time losses are occurring (not with hindsight); for practical guidance on building or responding to a mitigation position in your claim or counterclaim, Anderson Aylwin Begg & Co. can help with plain-language review of your situation and paralegal team support across Ontario, call (905) 686-8080 to get started.
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The Duty to Mitigate Including the Standard of Efforts to Do So
In a conscientious society, reasonably minded persons prefer to avoid waste; and accordingly, the law imposes the principle of mitigation, being a duty to mitigate, upon a harmed party. The duty to mitigate imposes a requirement upon a harmed person to act reasonably by taking steps that reduce or control losses and applies to all areas of law.
Note: Please contact Anderson Aylwin Begg & Co. by phone at: (905) 686-8080 to discuss any specific questions that you may have.
The Law
The duty to mitigate was articulated well by the Supreme Court within the case of Southcott Estates Inc. v. Toronto Catholic District School Board, [2012] 2 S.C.R. 675, where it was said that:
[23] This Court in Asamera Oil Corp. v. Seal Oil & General Corp., 1978 CanLII 16 (SCC), [1979] 1 S.C.R. 633, cited (at pp. 660-61) with approval the statement of Viscount Haldane L.C. in British Westinghouse Electric and Manufacturing Co. v. Underground Electric Railways Company of London, Ltd., [1912] A.C. 673, at p. 689:
The fundamental basis is thus compensation for pecuniary loss naturally flowing from the breach; but this first principle is qualified by a second, which imposes on a plaintiff the duty of taking all reasonable steps to mitigate the loss consequent on the breach, and debars him from claiming any part of the damage which is due to his neglect to take such steps.
[24] In British Columbia v. Canadian Forest Products Ltd., 2004 SCC 38 (CanLII), [2004] 2 S.C.R. 74, at para. 176, this Court explained that “[l]osses that could reasonably have been avoided are, in effect, caused by the plaintiff’s inaction, rather than the defendant’s wrong.” As a general rule, a plaintiff will not be able to recover for those losses which he could have avoided by taking reasonable steps. Where it is alleged that the plaintiff has failed to mitigate, the burden of proof is on the defendant, who needs to prove both that the plaintiff has failed to make reasonable efforts to mitigate and that mitigation was possible (Red Deer College v. Michaels, 1975 CanLII 15 (SCC), [1976] 2 S.C.R. 324; Asamera; Evans v. Teamsters Local Union No. 31, 2008 SCC 20 (CanLII), [2008] 1 S.C.R. 661, at para. 30).
[25] On the other hand, a plaintiff who does take reasonable steps to mitigate loss may recover, as damages, the costs and expenses incurred in taking those reasonable steps, provided that the costs and expenses are reasonable and were truly incurred in mitigation of damages (see P. Bates, “Mitigation of Damages: A Matter of Commercial Common Sense” (1992), 13 Advocates’ Q. 273). The valuation of damages is therefore a balancing process: as the Federal Court of Appeal stated in Redpath Industries Ltd. v. Cisco (The), 1993 CanLII 3025 (FCA), [1994] 2 F.C. 279, at p. 302: “The Court must make sure that the victim is compensated for his loss; but it must at the same time make sure that the wrongdoer is not abused.” Mitigation is a doctrine based on fairness and common sense, which seeks to do justice between the parties in the particular circumstances of the case.
Accordingly, the duty to mitigate requires a harmed person to minimize the harm suffered. Failure to minimize the harm may, and likely will, reduce the sum that the wrongdoer will owe the harmed person in a determination of liability at a court Trial. As was explained above by the Supreme Court in the Southcott Estates case, where a failure to mitigate occurs, it is the failure of the Plaintiff to act reasonably to minimize the loss that caused a portion of the harm. Simply said, where the Defendant does something wrong resulting in harm to the Plaintiff, the Defendant is responsible only for the portion of the harm that arises directly due to the wrongdoing of the Defendant and where a portion of the harm occurs or accrues because the Plaintiff failed to minimize that harm, the Plaintiff is at blame for the portion of the harm.
Conclusion
A Plaintiff (or Defendant within a counterclaim) is required to mitigate by taking reasonable steps to keep losses at a minimum. Where a Plaintiff fails to reasonably take steps to minimize losses, it is the inaction of the Plaintiff rather than the wrongdoing of the Defendant that caused such losses. When a Defendant to a lawsuit seeks to argue failure to mitigate as a defence strategy, the Defendant must include such an allegation with the defence pleading documents and it is the Defendant that must prove that the Plaintiff had a reasonable opportunity to mitigate the losses and failed to do so. However, the Plaintiff is without a requirement to mitigate perfectly and must only take such steps that are reasonable at the time that the loss is occurring rather than as may appear possible at a later date through hindsight.
NOTE: A significant quantity of online searches, such as “lawyers near me” or “best lawyer in,” typically indicates a pressing need for effective legal support rather than a specific job title. In Ontario, licensed paralegals are governed by the same Law Society as lawyers and are permitted to represent clients in particular litigation cases. Central to their function are advocacy, legal analysis, and procedural expertise. Anderson Aylwin Begg & Co. offers legal representation within its authorised parameters, focusing on strategic planning, evidence preparation, and compelling advocacy aimed at securing prompt and positive outcomes for clients.
