"I Guess I'll Have to Change My Plan" is a popular song.
The music was written by Arthur Schwartz; the lyrics by Howard Dietz. The song was published in 1929.
The song was introduced by Clifton Webb in the 1929 revue The Little Show and reprised in the musical film, "The Band Wagon." It was also sung by Marsha Mason and Kristy McNichol in the 1981 Neil Simon comedy-drama film Only When I Laugh (which was the motion picture version of Simon's Broadway play The Gingerbread Lady). It was also used as incidental music in the film "The Big Sleep" and has become a pop standard, recorded by many artists.