The Best Time to Visit Koh Samui

What's the best time to visit Koh Samui? When exactly is high season, when is low season, and when should you think twice? Koh Samui, in the Gulf of Thailand, has its own microclimate — its seasons differ noticeably from the Andaman coast, home to Phuket and Krabi. This guide goes month by month through what to expect. For the detail on temperatures, rain days and the monsoon explanation, see our Koh Samui weather article.

Koh Samui is a year-round destination

Koh Samui can basically be visited all year round — it's always warm, usually well above 28°C. The real difference between seasons isn't so much the temperature as the chance of rain, the crowds and the prices. Roughly: late December to April is high season, May to July the first low season, August a small mid-year bump ("Big Season"), and September to December the second low season, with the actual rainy season clustering towards the end of the year.

Month by month: weather, sea and prices

Here's how the climate data translates into practical travel planning:

High season and low season at a glance

The period from late December to the end of April is the busiest, even though April and May are the hottest months of the year. This high season (Peak and High Season) sees only a handful of rain days a month according to climate data — usually short showers before the sun returns. Hotels and scooter rental companies raise their prices during this time.

From May to July the first low season begins, and in August comes a small mid-year bump, the so-called "Big Season", as many visitors travel during the European summer holidays. From September, the second low season begins and runs until the end of December. The actual rainy season falls within this period.

When is the rainy season, really?

One reliable indicator: Thailand's national park authority closes Ang Thong Marine Park from 1 November to 15 December 2026, because the sea on the Gulf side is at its roughest during that stretch. For opening times and trips, see our Ang Thong National Park article. That lines up with the climate data: October and November statistically have the most rain days of the year. That doesn't mean it rains constantly — the rainy season on Koh Samui usually means heavier but time-limited showers rather than non-stop rain. For the full explanation of the monsoon pattern, see our weather article.

Festivals and events through the year

If you want to time your trip around a festival, these recurring dates are worth knowing:

• Songkran (Thai New Year): officially 13 to 15 April, with celebrations starting as early as 11 April in some places — the whole country joins in with water fights.
• Loy Krathong: a lantern festival held on the full moon of the 12th lunar month, falling on 24 November in 2026 — small floating baskets (krathongs) are set adrift on the water.
• Full Moon Party on Koh Phangan: held monthly on the full moon, roughly 9pm to sunrise, easily reached from Koh Samui by ferry.

Koh Samui or the Andaman coast?

One key difference from Phuket or Krabi: those sit on the Andaman coast and get their rainy season from the southwest monsoon, roughly May to October, peaking in September. Koh Samui sits on the Gulf side and is hit by the northeast monsoon instead — its rainy season falls in the opposite period, roughly October to December. So if you want to swim in Thailand during the northern-hemisphere summer without running into rain, Koh Samui is often the better call than the west coast — and vice versa in winter.

High season pick: an Ang Thong boat trip

The island's most popular boat trip only runs outside the closure period, so it's best booked during high season from January to March:

from 1,850 THBAngthong Marine Park Full-Day Speed Boat VIP Tour★★★★★4.71 from 391 reviews

Koh Samui month by month

Weather, sea, festivals and the right tours for every month in detail: January · February · March · April · May · June · July · August · September · October · November · December

Frequently asked questions

When should you avoid travelling to Koh Samui?

There's no fixed "bad" time, since it stays warm year-round. The period to avoid most is late October to late November, when rain days are statistically at their highest and Ang Thong National Park is closed from 1 November — especially if boat trips matter to you.

When is the best time to fly to Koh Samui?

For reliable weather and calm seas, high season from January to March is your best bet, with February the driest month at an average of just four rain days. Flights and hotels are also at their most expensive during this period.

Which is nicer, Phuket or Koh Samui?

That's down to taste, and both islands have their fans. Climate-wise, though, the comparison matters: Phuket, on the Andaman coast, has its rainy season from May to October, while Koh Samui, on the Gulf of Thailand, has its rainy season from October to December — travelling in the northern summer, you'll generally have better odds of dry weather on Koh Samui.

Which month is the coldest on Koh Samui?

December and January are the coolest, with nights around 24°C, though daytime temperatures still sit at a pleasant 28 to 29°C. Even in its coldest month, Koh Samui is far from cold by any northern European standard.

For getting there, see our article on how to get to Koh Samui, every festival of the year is covered in Top 10 Events in Thailand, and if you land in the rainy season, our Top 10 rainy day activities will help.