Thailand is one of the world's cheapest PADI Open Water destinations. Koh Tao alone certifies more divers per year than any other location globally.
On Koh Tao, you'll find PADI Open Water packages from ฿9,500–฿12,000 covering 4-day course with all equipment, materials, certification fee, and often shared accommodation. Popular schools: Big Blue, Crystal, Roctopus, Master Divers.
Phuket prices are slightly higher (฿13,000–฿18,000) due to higher operating costs, but you get more boat diving variety (Similan, Phi Phi). Best for combining cert with vacation.
Krabi and Khao Lak run similar prices to Phuket. Pattaya is cheapest in the Gulf side (~฿11,000) but visibility is more variable.
Advanced Open Water typically adds ฿7,000–฿10,000. Rescue Diver ฿9,000–฿12,000. Dive Master internships ฿35,000–฿60,000.
Best season: Andaman side (Phuket, Khao Lak) November–April. Gulf side (Koh Tao, Koh Samui) March–September.