A Day

A Day or A-Day may refer to:


 * 20 October 1944, the day the Leyte Island Operation began
 * A Day (film), a 2017 South Korean film
 * A-Day (University of Alabama), an annual college football exhibition game in the United States
 * A-day (6 April 2006), the commencement of pension tax simplification in the United Kingdom
 * "A Day", a 2017 episode of the American Netflix series Love