K-Day or KDAY may refer to:
Radio stations KDAY, in Greater Los Angeles, U.S. KDEY-FM, a simulcast KSRW (FM), in Independence, California, U.S., formerly KDAY-FM 1991–2004 KBLA, in Santa Monica, California, U.S., formerly KDAY 1956–1991
Other uses K-Day, a military designation of days and hours K-Day, an annual event at Michigan Technological University K-Days, an annual exhibition in Edmonton, Alberta, Canada Dayton International Airport, ICAO code KDAY