Vaishakha Shukla Chaturdashi is celebrated as Narasimha Jayanti. Lord Narasimha was the 4th incarnation of Lord Vishnu. On Narasimha Jayanti day Lord Vishnu appeared in the form of Narasimha, a half lion and half man, to kill Demon Hiranyakashipu.
The combination of Vaishakha Shukla Chaturdashi with Swati Nakshatra and weekday Saturday is considered highly auspicious to observe Narasimha Jayanti Vratam.
The rules and guidelines to observe Narasimha Jayanti fasting are similar to those of Ekadashi fasting. Devotees eat only single meal one day before Narasimha Jayanti. All type of grains and cereals are prohibited during Narasimha Jayanti fasting. Parana, which means breaking the fast, is done next day at an appropriate time.
On Narasimha Jayanti day devotees take Sankalp during Madhyahna (Hindu afternoon period) and perform Lord Narasimha Pujan during Sanyakal before sunset. It is believed that Lord Narasimha was appeared during sunset while Chaturdashi was prevailing. It is advised to keep night vigil and perform Visarjan Puja next day morning. The fast should be broken on next day after performing Visarjan Puja and giving Dana to Brahmin.
Narasimha Jayanti fast is broken next day after sunrise when Chaturdashi Tithi is over. If Chaturdashi Tithi gets over before sunrise then fast is broken any time after sunrise after finishing Jayanti rituals. If Chaturdashi gets over very late i.e. if Chaturdashi prevails beyond three-fourth of Dinamana then fast can be broken in first half of Dinamana. Dinamana is time window between sunrise and sunset.