1973 was a year in the 20th century.
- Thursday, March 15 (normal timeline): George McFly is honored.
- Thursday, March 15 (Biffhorrific timeline): George is murdered by Biff Tannen.
- (Biffhorrific timeline): Biff Tannen marries Lorraine Baines McFly.
- Unknown Date: Loretta is born to Lewis and his wife.
- Unknown Date: Ito T. Fujitsu known as "The Jits" is born.