"21 Reasons" is a song by English DJ/producer Nathan Dawe featuring vocals from British singer-songwriter Ella Henderson. It was released on 29 April by Atlantic Records (UK) and Warner UK for digital download and streaming. Written by Henderson, John Nicholas Ealand Morgan, Maegan Cottone, Dawe, Rune Reilly Koelsch and William Martyn Lansley, with production from Dawe and Punctual, "21 Reasons" features a prominent sample of Rune's 2003 dance song "Calabria". It is Henderson's second collaboration with Dawe since co-writing and having uncredited vocals on Dawe's 2020 single "Lighter" with rapper KSI.