Namaste Shrew
I recommend DrikPanchang :
Online Panchang, Panchangam and Hindu Calendar for the world
as the best and informative Panchang with alternatives in exceptional cases, and why.
e.g. what is SmArta EkAdashi versus VaishNav ekadashi? What is JanmAsTami , nishiddha kAla, GokuLAshTami/Nandotsav, how to calculate the nishiddha kAla as per different sAmpradAy (based on what they focus on - RohiNi nakshatra or tithi etc.)
If you like it and wish to use it, any little or one-time support from each user helps them maintain the site.
First, fasting purifies you and leads to spiritual progress. This is experienced first hand by many.
Scientific reason for ekAdashi fasting given by Swami ShivAnanda: As we know the moon has an effect on the ocean causing tides, so also on our minds. The 11th day gibbous moon has more effect on the body. If we fast on this day, it helps stay calm and prevent emotional upheaval caused by the moon. Thus helps with spiritual progress.
Spiritual Reasons for EkAsadhi from SmRuti (purANa and Mahabharat)
vana parva: When PAnDava had to live in the forest due to Duryodhan's atrocities, Shri KRshNa would visit them.
Yudhishtri asked KRshNa about the significance of each EkAdashi fast and KRshNa tells one story for each (fortnightly) ekAdashi that comes thru the year. Each story is from some past yuga where someone was facing tough times and how the ekadashi fast (as adviced by some Rshi) freed them of the difficulties, when observed with full faith, devotion.
It implies that Ekadashi purifies the jIva , burns off karma and increases bhakti (devotion - shraddha - faith, nishThaa - resolve.....)
Fasting is only a part of it. The biggest fasting rule is to avoid grains (and all mono or di-cotolydons)
UpavAs = upa + vaas = residing very close to your Self (AtmA) OR IshTa Dev, and in this case , NArAyaNa i.e. Lord VishNu for whom the fast is kept. Which means spend as much of the day giving special attention to BhagavAn VishNu , whichever way - meditate, think, japa, puja, read Geeta or BhAgvat..., Bhagvad-leelA, in short, stay with Him, close to Him.
Put all distractions aside, mind clutter, and stay with the
inner silence, meet the Lord there.
There is a site by devotees from New Zealand that you can subscribe to , and they will send you EkAdashi reminders with the story that KRshNa told YudhishThir -- pertaining to the specific EkAdashi.
Once Bheema , who was exceptionally strong, a wrestler, with an appetite, asked KRshNa for an easy solution where he does not have to fast on so many days in the year.
KRshNa tells him to only observe the nirjal ekAdashi, which came to be known as "PAnDav-nirjal" or "Bheema-nirjal" ekadashi.
Nirjal = without water. = Do not eat or dring anything on this one ekadashi in the year (falls in June) and Bheema is all set, he need not fast on any other day.