JUST LIKE CHRISTMAS DAY THEY HAVE FIXED UP ON THE 25TH DECEMBER, BUT OUR JANMASTAMI TITHI IS NOT FIXED UP LIKE THAT. MY BIRTHDAY IS ON THE 1ST SEPTEMBER, 1896, BUT THIS YEAR THE TITHI OF MY BIRTHDAY WAS FIXED FOR THE 4TH SEPTEMBER. SO IT IS VERY DIFFICULT TO CALCULATE, THEREFORE WE HAVE TO TAKE HELP FROM THE INDIAN EXPERT ALMANAC ASTRONOMERS.
69-09-30. Letter: Madhudvisa
Despite the common use of the new invented GBC calendar Srila Prabhupāda always use the Māyāpur Calendar. This calendar is perfectly calculated by Indian almanac astronomers as Prabhupāda states. So we need only one universal calendar for everyone on this earth.
Even the GBC is admitting that:
53. That the GBC accepts the Yoga Pitha Gaudiya Panjika calendar as authoritative for ISKCON on the instructions of Srila Prabhupada. It is also Srila Prabhupada’s instructions that the Panjika be followed in any time zone of the world according to the same Calendar date as observed in Mayapur. Bhakti Caru Swami shall secure and certify an official translation. [Provisional Order]
(GBC Resolutions February 25, 1988)
So it’s important we follow the correct dates otherwise we have to bear the consequences:
“IF ONE PERFORMS THE SRADDHA CEREMONY OF OBLATIONS TO THE FOREFATHERS ON THE EKADASI TITHI, THEN THE PERFORMER, THE FOREFATHERS FOR WHOM THE SRADDHA IS OBSERVED, AND THE PUROHITA, OR THE FAMILY PRIEST WHO ENCOURAGES THE CEREMONY, ALL GO TO HELL.”
“2. WHEN THERE IS AN IMPORTANT DVADASI, THE EKADASI FASTING IS TRANSFERRED ON THE DVADASI, AND THIS IS CALLED MAHADVADASI. THE 26TH OCTOBER, 1970, IS ACTUALLY DVADASI, SO THE FASTING IS OBSERVED TOGETHER, OR EKADASI FASTING IS DISREGARDED, AND THE DVADASI (MAHADVADASI) FASTING IS TAKEN AS IMPORTANT.
You were give this old Panjika just to consult the names and spelling only. The dates are different, so whatever date I have given, that is correct. WHY YOU ARE SEARCHING BYANJALI DVADASI IN THIS LAST YEAR’S PANJIKA? WHAT I HAVE GIVEN IS FROM THIS YEAR’S PANJIKA, SO EVERYTHING WILL NOT COLLABORATE.
5. 7th February, 1971–Varaha-Dvadasi, I have explained the position in regard to #2.
6. SO FAR DETERMINING EKADASI IT IS COUNTED 11 DAYS AFTER THE FULL MOON AND 11 DAYS AFTER THE NEW MOON, BUT SOMETIMES IT SO HAPPENS AS YOU HAVE NOTED ONE DAY LATER. HOWEVER, WHAT I HAVE GIVEN IS CORRECT.”
70-04-29. Letter: Pradyumna
In the last quote we can clearly see that Ekadasi is oriented on the waning and waxing of the moon. That is the same for everyone.
The Māyāpur Calendar u can find here:
Also here for ur apple device (iCal) :
“YOU SHOULD RECOMMEND THE AVOIDANCE OF MIXED EKADASI AND THE PERFORMANCE OF PURE EKADASI. YOU SHOULD ALSO DESCRIBE THE FAULT IN NOT OBSERVING THIS. One should be very careful as far as these items are concerned. If one is not careful, one will be negligent in executing devotional service.