"25 or 6 to 4" is a song written by the American musician Robert Lamm, one of the founding members of the rock/jazz fusion band Chicago. It was recorded for their second album, Chicago, in 1970, with Peter Cetera on lead vocals. The song was edited and released as a single in June that year, climbing to number four on the U.S. Billboard Hot 100 chart and number seven on the UK Singles Chart. It was the band's first song to reach the top five in the U.S. This recording features an electric guitar solo using a wah-wah pedal by Chicago guitarist Terry Kath, and has been included in numerous Chicago compilation albums.

An updated version of "25 or 6 to 4" was recorded for the 1986 album Chicago 18 with James Pankow listed as co-writer. With the new band member Jason Scheff on lead vocals, the single reached number 48 on the U.S. chart. This version was also used as the B-side for the band's next single in 1986, "Will You Still Love Me?".

The song is about trying to write a song in the middle of the night. The song's title is the time at which the song is set: 25 or 26 minutes before 4 AM. Because of the unique phrasing of the song's title, "25 or 6 to 4" has been incorrectly speculated to be a veiled reference to drug quantities, or a mystical allusion. The 1986 music video for the song references the correct meaning at its beginning.

In what may be a coincidence, the song's writer, Robert Lamm, had recently written and sung another Chicago hit, "Does Anybody Really Know What Time It Is?", for which this song's title can be seen to serve as an answer.

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