Here is the procedure to calculate Sahasra Chandra Darshan. The calculation of Sahasra Chandra Darshanam is not a touch task…
Sahasra Chandra Darshan (Sahasra Purna Chandrodayam) is the celebration of a person’s 1000th full moon during his or her life as a special occasion. As the time between similar lunar phases, the synodic month, is on average 29.53 days, this is usually celebrated in 82–83 years. This ritual is also known as Chandra Ratharohan.
In Sanskrit sahasra means 1000, purna means full, and chandrodyam means dawn of moon.
A similar kind of celebrations for elderly persons are Bhim Rathaarohan(in 77 years, 7 months, 7 days of age), Deva Rathaarohan (88 years 8 months, 8 days of age), Divya Rathaarohan (in 99 years, 9 months, 9 days of age), Mahadivya Rathaarohan (105 years 8 months, 8 days of age, Sashtiaapdapoorthi (or Shashti poorthi).)
This is a custom in India and Nepal. Mainly in Maharashtra, and some parts of North India, Andhra Pradesh and Karnataka, Sahasra Chandra Darshanam celebrations are celebrated.