The defendant carries the burden
Under 42 Pa.C.S. § 7102, the burden of establishing comparative negligence rests on the defendant, not the plaintiff. A plaintiff doesn't need to affirmatively disprove their own fault; the defendant has to prove it if they want it to reduce or bar the claim.
The Fair Share Act, in practice
Since Pennsylvania's Fair Share Act took effect in 2011, each defendant found liable is generally responsible only for the specific percentage of negligence the jury attributed to them — not a co-defendant's share as well. In a multi-defendant case, this means collecting the full judgment can require pursuing each defendant individually for their own portion, rather than collecting the entire amount from whichever defendant has the deepest pockets.
A genuinely separate doctrine: assumption of risk
Here's a real wrinkle worth understanding. In certain premises liability cases, Pennsylvania courts have allowed assumption of risk — framed as a "no duty" analysis rather than a comparative fault question — to act as a complete bar to recovery. Pennsylvania courts have not uniformly applied the Comparative Negligence Act to prevent this outcome, meaning assumption of risk can function as its own, separate total bar in some scenarios, distinct from the proportional 51% fault analysis that governs most other claims.
Why this distinction genuinely matters
Because assumption of risk can operate outside the ordinary comparative negligence framework in certain premises liability contexts, a claim that would otherwise survive the 51% bar analysis could still be barred entirely on this separate ground. Recognizing which doctrine actually applies to a specific set of facts is a genuinely important part of evaluating a Pennsylvania premises liability claim.
Who ultimately decides
If a case goes to trial, the jury determines the fault percentages that drive the 51% bar, while a judge may separately address whether assumption of risk applies as a threshold legal question. In the far more common scenario of a negotiated settlement, the parties and their insurers effectively work out these same questions between themselves. See our Pennsylvania comparative negligence calculator to see how sharply the outcome changes on either side of the 51% line.