Which episode is listed as overall episode number 125?

The How I Met Your Mother episode listed as overall episode number 125 is “Bad News.”

“Bad News” is the thirteenth episode of season 6 and originally aired on January 3, 2011. It follows Marshall and Lily as they seek help from a fertility specialist after months of unsuccessful attempts to conceive. The specialist, Dr. John Stangel, looks remarkably like Barney, creating one of the episode's central comic premises.

The episode is also remembered for its emotional ending. Marshall receives encouraging fertility news, only to learn that his father has suffered a fatal heart attack. The episode's title becomes especially meaningful because numbers appear throughout the story in a countdown from 50 to 1, quietly signaling that something devastating is approaching.

The surrounding entries help confirm the numbering: “False Positive” is episode 124, “Bad News” is 125, “Last Words” is 126, and “Oh Honey” is 127. That makes the stored answer unambiguous.