Basic Rules for understanding Vaisnava Calendar.
1. The Tithi at sunrise rules the day. 2. If the Tithi begins after
sunrise and ends before sunrise of the next day (Lost) it is
combined with the next Tithi. 3. If the same Tithi falls on sunrise
two days in a row, observances are scheduled on the first day;
except Ekadasi, Amavasya, or Purnima Tithis which are scheduled for
the second day.
Rules for Ekadasi :
Srila A. C.Bhaktivedanta Swami Prabhupada makes an interesting
comment in his purport to Sri Caitanya Caritamrta Madhya lila.
9-24-342: "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."
General Rules for observance are:-
1. Ekadasi must come in prior to the Arunodaya Viddhi (1hour, 12
mins, before sunrise). When it does so it is called Suddha Ekadasi
- pure ekadasi. If it begins after that, it is considered impure
and is therefore to be observed on the Dwadasi ( making Mahadwadasi
or Compounded) on the next day. 2. If Ekadasi falls on Sunrise two
days in a row, fasting is observed on the second day.
(If Mahadvadasi is in force, fasting is prohibited on the Ekadasi,
but the observance is done on the Dwadasi. Compound
Dwadasi-Mahadwadasi.) 1. If Ekadasi begins after sunrise and ends
before sunrise the next day it is considered Lost, too short, thus
not full, and impure. Therefore the next day is called Unmillani
Mahadwadasi. 2. If Dwadasi begins after sunrise and ends before
sunrise on the next day (Trayodasi), it is also Lost, and is to be
observed as Tri-Sprsa-Mahadwadasi. 3. If Dwadasi falls on the
Sunrise two days in a row the first Dwadasi becomes Vyanjuli
Mahadwadasi. 4. When the following Amavasya or Purnima falls on
sunrise two days in a row the preceeding Dwadasi becomes
Paksa-Vardhini-Mahadwadasi, Paksa based. Parama Ekadasi is in the
month of Purushottam.