Buffy the Vampire Slayer aired 144 total episodes.
The series ran for seven seasons, premiering on March 10, 1997, and concluding on May 20, 2003. Its 144-episode count covers the broadcast episodes that made up the complete television series, from the first-season opener "Welcome to the Hellmouth" through the finale "Chosen."
A common source of confusion is the unaired pilot episode, which is sometimes mentioned separately in episode guides. It is not included in the official total of 144 aired episodes. Another mix-up comes from counting later comic continuations as if they were television seasons; those expanded the story but were not broadcast episodes.
The show began on The WB, which carried its first five seasons. It then moved to UPN for seasons six and seven, before ending with Buffy and her allies confronting the First Evil. The finale also serves as the endpoint of the original television series, although the fictional universe continued in comics and the spin-off Angel.