Loy kratong is held on the full moon of the 12th month in the traditional thai lunar calendar.
In the western calendar , this uaually falls in November
During the night of the full moon, many people will float a small rafts (krathong) on the river or other body of water , such as canals, lakes and seas. Some people even float a raft on the river is to honor and pay respect to the goddess of water. Also, floating a raft in the river is to apologize to the goddess of the water for the bad things we have done to the river during the past year. That is why loy krathong is held at the end of the year. There also local and officially organised raft competitions, regarding its beauty and craftsmanship. In addition, there are also fireworks and beauty contests during the celebration of the festival.
Loi Kratong coincides with Lanna festival known as "Yi Peng". a multitude of Lanna-style sky lanterns (khom loi) are launched into the air where they resemble large flock of giant fluorescent jellyfish gracefully floating by thought the sky. The festival is meant as time for tham bun, to make merit.
The most elaborate Yi Peng celebrations can be seen in Chiang mai, the ancient capital of the former Lanna Kingdom, where now both Loi krathong and Yipeng are celebrated at the same time resulting in the lights floating on waters, and lights hanging from trees and buildings or standing on walls, and lights floating by in the sky.