Shani Pradosh or Sani Pradosha vrata is observed on Trayodashi tithi or the 13th day in Shukla Paksha or Krishna Paksha in a Hindu month which falls on Shanivar or Saturday. There are four Shani Pradosh in 2018. Each one in May, September and October.
Any Pradosha puja is performed by devotees during or after Suryasthamaya or sunset.
The main purpose of Sani Pradosha vrat is to pacify the bad effects of Lord Shani who is also known as one of the most powerful and effective Navagraha or nine celestial Gods.
Sani Pradosham in 2018
Saturday, 26 May 2018 – Shani Pradosh Vrat in Shukla Paksha
Saturday, 22 September 2018 – Shani Pradosh Vrat in Shukla Paksha
Saturday, 6 October 2018 – Shani Pradosh Vrat in Krishna Paksha