About Two Krishna Janmashtami Dates
Most of the time, Krishna Janmashtami is listed on two consecutive days. The first one is for Smarta Sampradaya and other one is for Vaishanava Sampradaya. Vaishanava Sampradaya date is the latter one. A single date for Janmashtami means that both Sampradaya would observe Janmashtami on the same date.
However many people will notice unanimity in North India on choosing the day to celebrate Krishna Janmashtami. The reason behind this unanimity is the institution of ISKCON. The International Society for Krishna Consciousness, commonly known as ISKCON is founded on the principles of Vaishnava traditions and most followers of the ISKCON are the followers of Vaishnavism.
With all due respect, ISKCON is one of the most commercialized and global religious institutions which spend money and resources to promote ISKCON brand and ISKCON culture. In North India most people observe Janmashtami on the day chosen by ISKCON. Many people who are not the followers of Vaishnavism don't even understand that ISKCON traditions are different and the most appropriate day to observer Janmashtami fasting might not be same as that of ISKCON.
Smarta followers who understand the difference between Smarta and Vaishnava sectarian don't follow ISKCON date to observer Janmashtami fasting. Unfortunately ISKCON date to observer Janmashtami is unanimously followed in Braj region and most common people who just follow the buzz observe it on the date followed by the ISKCON.
People who are not the followers of Vaishnavism are followers of Smartism. Hindu religious texts like Dharmasindhu and Nirnaysindhu have well defined rules to decide Janmashtami day and those rules should be followed to decide Janmashtami day if one is not the follower of Vaishnava Sampradaya. Ekadashi fasting is one of the good examples to understand this difference. Rules to observe Ekadashis' fasting are also different for Smarta and Vaishnava communities. However there is more awareness about different Ekadashi rules followed by Vaishnava sectarian. Not only Ekadashis, Vaishnava fasting day for Janmashtami and Rama Navami might be one day later than Smarta fasting day.
The followers of Vaishnavism give preference to Ashtami Tithi and Rohini Nakshatra. The followers of Vaishnavism never observe Janmashtami on Saptami Tithi. Janmashtami day according to Vaishnava rules always fall on Ashtami or Navami Tithi on Hindu calendar.
However rules followed by Smartism to decide Janmashtami day are more complex. The preference is given to Nishita or Hindu midnight. The preference is given to the day, either Saptami Tithi or Ashtami Tithi, when Ashtami Tithi prevails during Nishita and further rules are added to include Rohini Nakshatra. The final consideration is given to the day which has the most auspicious combination of Ashtami Tithi and Rohini Nakshatra during Nishita time. Janmashtami day according to Smarta rules always fall on Saptami or Ashtami Tithi on Hindu calendar.
This page list Janmashtami according to Smarta Sampradaya and make a footer note if it doesn't coincide with Janmashtami day observed by the ISKCON.
Krishna Janmashtami is also known as Krishnashtami, Gokulashtami, Ashtami Rohini, Srikrishna Jayanti and Sree Jayanthi.