You may see this phrase in a lawyer's letter, a court filing, or a conversation about whether a case was filed "on time." It usually comes up when the harm was not obvious right away. The discovery rule is the idea that the clock for a legal deadline may start when a person knew, or reasonably should have known, about an injury and its likely cause, rather than on the exact day the underlying event happened.

That matters because most claims are controlled by a statute of limitations. If an injury stays hidden for months or years, a strict deadline based only on the original event can cut off a case before the injured person even knows there is one. Lawyers and judges use the discovery rule to argue about when the claim actually "accrued," what warning signs existed, and whether a reasonable person would have connected the injury to the defendant's conduct sooner.

In New York, the rule is limited and very case-specific. New York generally uses fixed filing deadlines, but some claims get a discovery-based start date under statutes such as CPLR 214-c for latent effects of exposure to toxic substances, and CPLR 214-a for certain medical malpractice cases involving a foreign object left in the body. In an injury case, that timing issue can decide whether a lawsuit survives at all, even before the court reaches liability or damages.