Ontario Limitation Period Discoverability

The Discoverability Principle

Before Ontario enacted the Limitations Act, 2002, S.O. 2002, c. 24, Sch. B, limitation periods typically ran from the date the cause of action arose — often before the plaintiff had any reasonable basis to know a claim existed. Courts developed the equitable discoverability doctrine to prevent injustice, but its scope was uncertain and varied by cause of action.

The 2002 Act codified a universal discoverability rule. Under s. 5(1), a claim is discovered on the earlier of:

1. The day the claimant first knew all four elements of the s. 5(1)(a) test; and
2. The day a court determines the claimant first ought to have known those elements, applying the reasonably diligent person standard under s. 5(1)(b).

The four elements that must be known (or ought reasonably to have been known) are: (i) that the injury, loss or damage occurred; (ii) that it was caused or contributed to by an act or omission; (iii) that the act or omission was that of the defendant; and (iv) that the proceeding would be an appropriate means to seek remedy.

The Four Elements of Discovery Under Section 5

Element 1: The Injury, Loss, or Damage

The plaintiff must know (or ought to know) that an injury, loss, or damage actually occurred. This element prevents the limitation from running before any loss is manifest. In latent injury cases — asbestos disease, long-term medication side effects — the clock does not start until the plaintiff knows the disease or harm exists.

Element 2: Causation by an Act or Omission

The plaintiff must know that the loss was caused by an act or omission — not merely that a bad outcome occurred. In medical malpractice cases, the limitation typically runs not from the date of the negligent procedure but from when the plaintiff knew (or ought to have known) the outcome was caused by professional conduct rather than being a known complication or risk. See Pirner v McTavish 2018 ONCA 859.

Element 3: Identity of the Defendant

The plaintiff must know that the act or omission was that of the defendant specifically. Where the identity of the responsible party is genuinely unknown — for example, where a John Doe defendant or an unidentified manufacturer is involved — the limitation period does not run until identity becomes known or reasonably discoverable.

Ontario courts have applied this element where plaintiffs had knowledge of harm but not of which corporate entity in a group was the actual defendant, holding the limitation postponed until the specific entity was identified. See Ferrara v Bernardi2020 ONCA 38.

Element 4: Appropriateness of a Legal Proceeding

The plaintiff must know that a legal proceeding would be an appropriate means to seek remedy for the loss. This element was controversial — courts debated whether it merely described when a claim was legally cognizable or whether it required the plaintiff to have reason to believe litigation was a practical option.

The Supreme Court of Canada resolved this in Grant v Torstar Corp [2009] 3 SCR 640 and clarified the element in Presidential MSH Corp v Marr Foster & Co LLP2017 ONCA 325. The appropriateness element is satisfied when the plaintiff knows (or ought to know) that the defendant's conduct may give rise to legal liability — the plaintiff need not have sought legal advice or received confirmation of a viable claim.

The Objective Knowledge Standard

Section 5(1)(b) of the Limitations Act introduces the objective limb: the claim is discovered when a reasonably diligent person with the abilities and in the circumstances of the claimant first ought to have discovered those elements.

The standard is objective but person-specific — the court asks what this claimant, with their actual circumstances and characteristics, ought reasonably to have discovered. This means that a plaintiff with fewer resources, less education, or who speaks limited English is not held to the same standard as a sophisticated corporate plaintiff with access to legal counsel.

The leading Ontario Court of Appeal case is Lawless v Anderson 2011 ONCA 102, confirming that the objective standard requires courts to consider the actual circumstances of the plaintiff, not a hypothetical average person. Courts consider what information was available, what steps a reasonably diligent person in that position would have taken, and what knowledge would have resulted from those steps.

Plaintiffs who unreasonably delay seeking medical diagnosis, who ignore obvious signs of damage, or who fail to investigate when clearly on notice of a potential problem may be deemed to have discovered the claim before they subjectively acknowledged it.

Wilful Concealment and Fraudulent Misrepresentation

Section 5(1)(a)(iv) and s. 5(2) of the Limitations Act address situations where a defendant's conduct prevented the plaintiff from discovering the claim. Where the person against whom the claim is made wilfully concealed facts that the claimant needed to know, the limitation does not begin to run until the concealment ends or the claimant discovers the concealed facts.

Ontario courts have applied the concealment principle broadly in professional negligence cases where lawyers or accountants misled clients about the status of matters, and in product liability cases where manufacturers suppressed knowledge of defects. The defendant's conduct must be something more than simple non-disclosure of a potential claim — active concealment, misrepresentation, or deliberate steps to prevent discovery are required.

The concealment tolls the limitation period prospectively — once the plaintiff discovers (or ought to discover) the concealed facts, the two-year period begins running from that point. The concealment does not reset the ultimate 15-year period under s. 15.

Postponement for Minors

Section 6 of the Limitations Act postpones the running of the basic two-year limitation period for a claimant who was a minor (under 18) when the claim arose. The limitation period does not run while the claimant is a minor. Once the claimant turns 18, the two-year period begins running — even if the minor had subjective knowledge of the claim earlier.

Critical distinction: s. 6 postpones the basic limitation period only. The ultimate 15-year limitation period under s. 15 is not postponed for minors. If the act or omission occurred when the child was young and more than 15 years have passed since then, the ultimate limitation may have expired before the child turns 18 — leaving no claim available.

This produces harsh results in cases involving historical abuse of young children. Ontario courts have grappled with constitutional challenges to the 15-year ultimate limitation in childhood abuse cases, though it was upheld in M (K) v M (H)[1992] 3 SCR 6 under the pre-2002 law (incest). Post-2002 cases have generally enforced the ultimate limitation despite its harsh application to minors.

Postponement for Incapacity

Section 7 of the Limitations Act postpones the basic two-year period for a claimant who was incapable of commencing a proceeding on the date the claim was discovered, and is not represented by a litigation guardian. The period is postponed until the earlier of:

• The day the person ceases to be incapable
• The day a litigation guardian is appointed for the person

"Incapable" is defined in s. 7(2) with reference to the Substitute Decisions Act, 1992 — broadly, the inability to understand information relevant to making a decision or to appreciate the consequences of a decision. Cognitive impairment, dementia, and severe mental illness may qualify.

As with the minor's postponement, the s. 7 postponement does not extend the ultimate 15-year limitation under s. 15. Incapacity cannot revive an expired ultimate limitation. This can leave permanently incapable persons without any claim if the ultimate period has expired before incapacity terminates or a litigation guardian is appointed.

The Ultimate 15-Year Limitation Period

Section 15 of the Limitations Act establishes that no claim may be brought more than 15 years after the day on which the act or omission on which the claim is based took place. This is an absolute backstop — it runs regardless of discoverability, regardless of the plaintiff's knowledge, and (with very limited exceptions) regardless of postponements.

The 15-year ultimate limitation is subject to suspension only in limited circumstances under s. 15(4)–(6): wilful concealment by the defendant, or claims arising from sexual assault, other specified assaults, or breach of duty by a person in a position of trust or authority. For those excepted claims, there is no ultimate limitation — the basic two-year period applies from the date of subjective or objective discovery, potentially running for decades.

The practical effect of s. 15: even where the plaintiff had no actual knowledge of the claim, and had no reasonable basis to suspect it existed, the claim is permanently extinguished 15 years after the event. Courts have no discretion to extend the ultimate period except as specifically provided in the Act.

Discoverability in Specific Practice Areas

Agreements to Vary and Contracting Out

Section 22 of the Limitations Act prohibits contracting out of the Act in consumer agreements. However, business parties may agree to vary limitation periods — either shortening or lengthening them — within the Act's framework. Agreements to shorten limitations are enforceable between commercial parties provided they are clear and the shortened period is not unconscionably brief.

A common issue in construction and service contracts: contractual notice provisions that require written notice of claims within a very short window (e.g., 30 days of the event giving rise to the claim) operate as contractual conditions precedent, not limitation periods — but failure to comply forfeits the claim regardless of the statutory limitation. Courts have enforced these clauses strictly where the parties had equal bargaining power.

Importantly, parties can also agree to extend or suspend the running of a limitation period through a standstill agreement — this is common in commercial disputes where parties are engaged in settlement negotiations and want to preserve the option of litigation without the pressure of an approaching limitation date.

Frequently Asked Questions