The best time to visit Thailand is November to February, when the Andaman coast is dry and the north is cool. The Gulf coast (Samui, Phangan, Tao) is best from January to August. There is no single best month for the whole country — the two coasts run on different calendars.
The short version
- November–February: best overall, dry on the Andaman, cool in the north, highest prices.
- March–May: hot everywhere; the Andaman still works, the north is hazy.
- June–October: green season on the Andaman, but the Gulf is often lovely.
- The Gulf's rainy season is October–December — the opposite of the Andaman.
The three seasons
Cool and dry runs from November to February. It is the peak, the most expensive and the most reliable: 25–32°C, low humidity, calm seas on the Andaman.
Hot season is March to May, with temperatures in the high 30s and Songkran in mid-April. It is quieter and cheaper, and the Andaman is still swimmable.
Green season is June to October. Rain comes in heavy afternoon bursts rather than all day, prices drop 30–50%, and the landscape is at its best.
Two coasts, two calendars
The Andaman coast (Phuket, Krabi, Phi Phi, Koh Lanta, the Similans) is best from November to April. From May to October the swell makes boats uncomfortable and some islands close.
The Gulf coast (Koh Samui, Koh Phangan, Koh Tao) runs later: its wet season is October to December, and it is often excellent in June and July when the Andaman is rough.
What we would actually book
For a first trip combining culture and beach, late November to early February is the safest window. Book six to nine months ahead for the Christmas period.
If you want lower prices and do not mind an afternoon downpour, late June or September is underrated — particularly in the north, where the rice fields are green and the temples are empty.
What we tell people with fixed dates
Most travellers do not choose the month, the month chooses them — school holidays, a work gap, a wedding. In that case the useful question is not 'when is the best time' but 'given these dates, which coast'. That single decision fixes about 80% of the trip.
If you are travelling between November and February, either coast works and the north is at its best; book early, because everyone else knows this. March to May: go to the Andaman, and treat the north as a city-and-food stop rather than a mountain one. June to September: the Gulf is the reliable coast, with Samui, Phangan and Tao at their best in July and August. October is the awkward month on both coasts, and the one where we suggest Bangkok, Chiang Mai and Kanchanaburi instead of a beach.
One caveat worth stating plainly: Thailand's monsoon is not a British winter. A green-season day is usually sunny until 2pm and wet for ninety minutes, then clear again. If you can tolerate that, May to October buys you 30–40% off the same hotels and half the crowds.
