Thailand has three broad seasons – cool-dry (Nov–Feb), hot (Mar–May) and rainy (Jun–Oct) – but they don't hit every region at the same time. The Andaman coast (Phuket, Krabi) and the Gulf islands (Samui, Phangan) even run opposite monsoons. Below is how to pick your window.
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Add it in the trip planner →This is the classic window and, for most first-timers, the right one. Skies are clear, humidity drops and the whole country – Bangkok, the north and the beaches – is comfortable. December and January are the driest and coolest, which is exactly why they're also the busiest and most expensive: expect resort rates on the islands to double over Christmas and New Year, and book flights and hotels well ahead. If you want blue-sky beach photos and can absorb the crowds, this is your season. See how it shapes a route in our 2-week itinerary.
From March the mercury climbs, peaking around Songkran (Thai New Year, 13–15 April) when the country erupts into a nationwide water fight. Daytime highs of 35–40°C in Bangkok and the interior are real, and this is also when farmers burn fields in the north – Chiang Mai and Chiang Rai suffer heavy smoke haze in March, sometimes worse than city smog. Beaches stay bearable thanks to sea breezes, so this is a fine time for the islands but a poor one for trekking up north.
Don't write it off. Rain usually arrives as intense afternoon downpours that clear within an hour or two rather than all-day grey, and you get lush scenery, waterfalls in full flow, thin crowds and the year's lowest prices – often 30–50% off resort rates. September and October are the wettest. The trade-off is unreliable ferry days and the occasional washed-out beach afternoon. For budget travellers with flexible plans, it's the best value on the calendar; see our trip cost guide.
Thailand's great weather hack is that its two coasts run on opposite clocks. The Andaman side (Phuket, Krabi, Koh Lanta, Koh Phi Phi) is at its best November–April and wettest May–October. The Gulf side (Koh Samui, Koh Phangan, Koh Tao) is driest roughly January–April and August–September, with its heaviest rain in October–November. So if you're travelling in, say, October, skip the Andaman and head for the Gulf. More on this in our island-choosing guide.
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Nationally, September and October are the wettest, though it varies by coast. On the Gulf islands (Samui, Phangan, Tao) the peak rain actually comes later, in October and November, while the Andaman coast is wettest from May to October.
Yes, for many travellers. Rain usually falls in short afternoon bursts, the landscape is green, crowds thin out and prices drop sharply. Keep plans flexible around ferry crossings and you'll get excellent value. See our weather guide for detail.
Songkran (Thai New Year) runs 13–15 April. It's a joyful nationwide water fight – fantastic fun if you embrace it, chaotic if you're trying to travel or keep your phone dry. Book accommodation early and expect transport to be busy.