A Day or A-Day may refer to:
A day, one rotation of the Earth 20 October 1944, the day the Leyte Island Operation began A-Day (University of Alabama), an annual American college football exhibition game, established in 1946 "A Day", a 1985 song by Clan of Xymox on their self-titled debut album, released as a single multiple times, and used on The Guest film soundtrack (2014) A-day (6 April 2006), the commencement of pension tax simplification in the UK A Day (film), a 2017 South Korean film "A Day", a 2017 episode of the American Netflix series Love
See also One Day (disambiguation)