Ekadashi falls twice in every lunar month, on the eleventh tithi of the waxing fortnight and again of the waning fortnight, giving roughly twenty-four observances a year. The fast ranges from complete abstention to a diet that simply excludes grains, beans and certain vegetables. Devotees spend the day in recitation and temple visits and break the fast the next morning during a prescribed parana window, after the tithi has ended but before it is too late in the day.
Each Ekadashi carries its own name and story, such as Nirjala, Devshayani, Prabodhini and Vaikuntha, and the associated merit is described in the Puranas. Because the eleventh tithi may not cover sunrise on a single day, Vaishnava and smarta calendars sometimes place the fast on different dates, and the strict Vaishnava rule shifts it to the following day when the tithi is "viddha," mixed with the tenth at dawn.