The best time to go to Koh Tao is during the dry season, which typically runs from March to May and from July to September. These periods offer the most consistent sunny weather and calm seas, which are ideal for enjoying the island's main attractions.For those planning to spend their days diving or snorkelling, the months of March to May often provide excellent underwater visibility and warmer water temperatures. This is when you're most likely to see a wide range of marine life. The seas are usually very calm, making boat trips and water activities more comfortable.If your preference is for sunbathing and enjoying the beaches, July to September is also a fantastic time. While there might be an occasional short shower, these usually pass quickly, leaving plenty of sunshine.