Sometimes the Calendar is marked Ekadashi with two consecutive days. In that case, if you read closely, you will find first day may be marked as Smarta Ekadasi and next day marked as Bhagavat or Vaishnava.
First of all what is Smarta?
Smarta, refers to nonsectarian denomination of Hinduism, which does not see difference between Vaishnava, Shaiva or Shakti. They accepts Brahman (different than Brahmin) as source of all deities. It is also called ancient Vedic Hindu Religion.
Most Hindus today are Smarta.
The adherents who follow the Vedas and Shastras are, in this regard, called Smarta. Smartas are, therefore, followers and propagators of or religious texts derived from Vedic scriptures. Smarta religion is practiced by people who believed in the authority of the Vedas as well as the basic premise of puranas. Smartas believe that the worshiper is free to choose a particular aspect of God to worship, to the extent that the worship practices do not contradict the Vedas and the Smritis. So, in that sense, an orthodox smarta is unlikely to view gods of non-vedic religions favorably, even though he may hold the religion acceptable to its own traditional followers
Vaishanv or Bhagvat, refers to Vishnu as supreme being. The denomination in Hinduism that believes Vishnu as supreme lord where everything begins and ends in.
Now lets see how that differs for Ekadashi.
Ekadasi has two rules: Smartha and Vaishnava. The Smarta rule is simple – ekadasi should be visible at the time of local sunrise. The vaishnava follows ekadasi that is not contaminated by Dashami thithi. In other words, to the Vaishnavaites, ekadasi should be prevailing two hours before sunrise.
Bhagavata, or Vaishnava, Ekadashi observance is based on the rule that Dasami or the tenth day during a lunar fortnight should have ended before Arunodaya (96 minutes period before sunrise on the Ekadasi or the 11th day in a lunar fortnight). Vaishnava fasting day might be one day after of Smartha fasting day.
The Smarta rule is simple – ekadasi should be visible at the time of local sunrise. The vaishnava follows ekadasi that is not contaminated by Dashami thithi. In other words, to the Vaishnavaites, ekadasi should be prevailing two hours before sunrise.
Bhagavata, or Vaishnava, Ekadashi observance is based on the rule that Dasami or the tenth day during a lunar fortnight should have ended before Arunodaya (96 minutes period before sunrise on the Ekadasi or the 11th day in a lunar fortnight).
Per Antaryamin, Ekadashi fasting spans for three days. Devotees take single meal in the afternoon a day before fasting day to make sure there is no residual food in the stomach on next day. Devotees keep strict fast on Ekadashi day and break the fast on next day only after sunrise. Eating of all type of grains and cereals is prohibited during Ekadashi fasting.
Good Reads :
https://answers.yahoo.com/question/index?qid=20120911213736AAIgXie
https://antaryamin.wordpress.com/2012/02/26/smartha-vs-vaishnava-traditions-and-their-ekadasis/
