"I Won't Last a Day Without You" is a song by Carpenters with lyrics written by Paul Williams and music composed by Roger Nichols.

The writing duo had previously contributed "We've Only Just Begun" and "Rainy Days and Mondays" to the Carpenters.

The song was written by Paul Williams (lyrics) and Roger Nichols (music) who also wrote two previous hits for Carpenters – "We've Only Just Begun" and "Rainy Days and Mondays".

[1] Williams said that the song was originally written with just two verses and a chorus, and a demo was submitted to Carpenters in 1971.

However, just before the song was due to be recorded, a request was sent to the songwriters for an additional bridge and a third verse to be added.