Pennsylvania's rule: barred only when you exceed the defendant
Under 42 Pa.C.S. § 7102(a), a plaintiff's own negligence does not bar recovery unless they are more negligent than the defendant (or, with multiple defendants, more negligent than their combined share). Damages are reduced in proportion to the plaintiff's own degree of fault — but only once that fault actually exceeds 50% does recovery get barred entirely. Pennsylvania law places the burden of establishing comparative negligence on the defendant, not the plaintiff.
Worked example
Someone with $100,000 in damages, found 49% at fault, recovers $51,000. That same person, found exactly 50% at fault instead, still recovers $50,000. Found at 51%, that same person recovers nothing at all.
The 2011 Fair Share Act: several liability, not joint and several
Since Pennsylvania's Fair Share Act took effect on June 28, 2011, each defendant is generally only liable for the percentage of negligence the jury actually attributed to them — not a co-defendant's share as well. This several-only approach to liability represents a real shift from the older joint-and-several model, with Pennsylvania treating governmental entities somewhat differently within this same framework. See our full guide to how fault is assigned in Pennsylvania for more on this, and a separate, distinctive wrinkle involving assumption of risk.