The song is noted for its live performances; guitarist the Edge and bassist Adam Clayton trade instruments during performances of it, and as it was commonly played to end their concerts, the band would leave the stage one-by-one as the audience continued to sing the refrain "How long to sing this song?".

Another band, Minor Detail, were scheduled to start their recording session at 8 a.m. and had arrived early,[4] and U2 bassist Adam Clayton had already gone home.

Producer Steve Lillywhite quickly did a multi-track edit of the song, removing any parts that seemed disconnected from the main musical idea.

[4] "40" debuted live on 26 February 1983 in Dundee as the final song of the show, and closed every single concert on 1983's War Tour.

Between January 1990 and March 2005, full performances of "40" were extremely rare, though on 2001's Elevation Tour, it was regularly snippeted at the end of "Bad" before the song segued into "Where the Streets Have No Name".

[9] "40" was also played as the closing song at the final show of U2's 2023–2024 concert residency, U2:UV Achtung Baby Live, at Sphere in the Las Vegas Valley.