That makes Samui one of the few Thai beach islands that works in July, and one of the few you should think twice about in November. It is also one of the five places travellers add most often across the more than 268,000 Thailand trips planned with Stippl, so plenty of people are already fitting it around exactly this calendar. Here is the year, season by season and month by month.
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Download the appWhen is the best time to visit Koh Samui? The short answer
Go between February and April if you want the safest bet on sun. These are the driest months of the year, the sea is flat and every boat and day trip is running.
January and May to August are good too. January is still shaking off the last of the rain, and the summer months bring frequent but short showers rather than washed-out days. That summer stretch is the big one to know about: while Phuket, Krabi and the rest of the Andaman coast sit in their wet season, Samui is the Thai island that still works for a beach trip.
October to December is the time to think twice. This is Samui's rainy season, with the heaviest rain of the year, rough seas and the odd cancelled ferry. You can still go, but plan it with flexible days, or switch coasts.
| Best months | February, March, April |
| Good months | January, May, June, July, August |
| In between | September |
| Wettest months | October, November, December |
| Busiest and priciest | Christmas and New Year, then the dry season and the northern summer holidays |
Koh Samui seasons
Daytime temperature is not really a reason to pick one month over another here: it is warm all year, and slightly hotter around April and May. What changes is the rain, the wind on the water and how busy the island gets. That gives you three Koh Samui seasons, each with a clear verdict.
The dry season: January to April
This is the Koh Samui dry season in the tourist calendar, and February to April is the true dry core: sunny days, few rain days and calm water. It gets steadily hotter towards April. January belongs here for crowds and prices, but the weather is still settling: it is a good month, not yet a dry one, and the northeast swell can still cancel the odd boat.
Koh Samui high season falls here, and again around Christmas and New Year. Book rooms early if your dates are fixed, especially for a beachfront stay in Chaweng or a quiet bay near the airport in Choeng Mon.
This is also the best stretch for the island's signature day trip, Ang Thong National Marine Park, a group of limestone islands you can only reach on an approved tour boat. A big boat day costs about €29 to €39 (1,100 to 1,500 ฿), plus a park fee of about €8 (300 ฿) in cash that most tours leave out. You can compare Ang Thong day trips on GetYourGuide.
Summer: May to August
Hot, green and mostly sunny, with short showers on many days, usually in the afternoon. Those showers rarely ruin a beach day, and the sea is at its calmest of the year for the boats. May is a quieter month between the dry season peak and the summer holidays; July and August get busy again with families on school holidays from the northern hemisphere.
This is when Samui earns its place on a summer trip. The Andaman coast takes the southwest monsoon from roughly May to October, so in these months Samui is simply the right island.
One honest note: box jellyfish are a real, if rare, risk in the Gulf, mostly from July to October. Swim where locals swim, ask at your hotel about the beach, and know that vinegar is the first aid.
Koh Samui rainy season: September to December
The Koh Samui rainy season starts later than anywhere else in Thailand. September is still mostly fine, with more frequent showers as the month goes on. From October the northeast monsoon arrives, and October to December carries about half of the island's rain for the whole year, with November the wettest month by a distance.
This is the real Koh Samui monsoon season, and the wind matters as much as the rain. Rough seas can cancel boats to Koh Phangan and Koh Tao, and Ang Thong Marine Park closes every year from the start of November until mid December. On the plus side, rooms are at their cheapest and the beaches at their emptiest, especially in October and November.
Koh Samui weather by month
If you already know your month, here is the verdict for it.
January and February
January is a good month with a catch: the rain is fading but has not quite gone, and the sea can still be choppy after the monsoon. By February the island is dry and bright, and it is one of the best months of the whole year. Both months sit in peak season, so prices are high.
March and April
The Koh Samui weather in April and March is the driest and calmest of the year, with the fewest rainy days and flat water for boat trips. April brings the hottest days. Songkran, the Thai New Year water festival in mid April, turns the streets cheerful, busy and very wet, so keep your phone in a dry bag if you head out.
May to August
Good beach weather with the odd shower, and quieter than the winter peak, especially in May and June. The boats run smoothly and the sea is calm. July and August are the busiest summer months, when the island fills up with families on holiday.
September
The Koh Samui weather in September is still mostly fine. Showers come more often, especially towards the end of the month, and in some years the wet season opens a little early. Crowds thin out after the summer holidays, which makes it a decent month for a quieter, cheaper stay if you can live with some rain.
October and November
This is the stretch to plan carefully. The Koh Samui weather in November is the wettest of the year, and October is not far behind, with heavy downpours, rough seas and ferries that can be cancelled at short notice. Some night markets simply do not open after a heavy afternoon of rain, so ask your hotel to check before you go out.
Koh Samui in November is cheap and quiet, but if you want guaranteed sun, pick the Andaman coast instead. Our guide to Thailand in November explains why the west coast and the north come good just as the Gulf turns wet.
December
The Koh Samui weather in December is often still wet early in the month and improves towards the end, though it stays one of the rainier months. Ang Thong reopens in mid December. Christmas and New Year are the busiest and most expensive weeks of the year whatever the weather, so book early if you want to be here for them. For the whole country that month, see Thailand in December.
When not to go to Koh Samui, and where to go instead
If reliable sunshine is the point of your trip, avoid October to December. That is the wettest period on the Gulf, and also the time when boats are most likely to be cancelled.
The good news is that you do not have to cancel Thailand, you switch coasts, and our guide to the best time to visit Thailand shows how the two sides trade places through the year. From roughly November to April the Andaman islands are in season: Koh Lanta is the slow island, built for three to five lazy nights, and Koh Lipe in the far south is a small island with no roads, where you walk everywhere. A trip that starts in Bangkok can just as easily head west as east, and our Thailand guide shows how the two coasts fit into one route.
Koh Samui or Phuket?
Neither is better: they suit different trips, and they have opposite calendars. Samui is the calmer island, with easy boat hops to Koh Phangan and Koh Tao. Phuket is bigger, with more beaches, more nightlife and more day trips within reach.
So choose by the month you travel. Phuket is at its best roughly November to April, and Samui roughly January to August, with February to April the one window when both are dry. For beaches, cost and flights side by side, read our Koh Samui vs Phuket comparison.
Combining Samui with Koh Phangan and Koh Tao
The three Gulf islands share the same seasons, so whatever month works for Samui works for its neighbours too. They combine easily by boat in one trip, and the summer variant of our two week Thailand itinerary puts all three after Bangkok and Chiang Mai.
- Koh Phangan is about 30 minutes away by catamaran, for about €9 (350 ฿). It is the home of the Full Moon Party; boats around party nights sell out two to three weeks ahead.
- Koh Tao is about an hour and a half by catamaran, for about €17 to €20 (650 to 750 ฿). It is the diving island, and the crossing that gets cancelled most in rough weather.
- Koh Samui is the easy anchor: the only one of the three with its own airport, so it is the natural place to start or finish.
How many nights on Koh Samui?
Travellers who plan Koh Samui with Stippl most often stay three nights, and more than one in five stays five nights or longer. Samui is a place people stay, not a place they pass through, and that makes sense: a one night stay costs you the same travel days as a five night one.
Three nights covers the island: one day for the temples in the northeast, one for a boat trip, one for the beach or the interior by scooter. Five nights lets you actually use it, with time for a day on Koh Madsum or a lazy beach day. Add more if you are combining it with Koh Phangan or Koh Tao.
Read more: things to do on Koh Samui
Plan your Koh Samui trip with Stippl
Once you know your month, put Samui in a route that matches the season. In the Stippl itinerary planner you add Koh Samui and its neighbours to one trip, set the nights per stop, and add the flights and boats between them, so you can see straight away whether a ferry day lands too close to your flight home.
Describe your trip, get a Koh Samui itinerary in seconds
Everything in this guide is already in Stippl. Tell the planner how long you have and what you like: it builds the route, the days and the travel times, and you edit whatever you want.
Planning in October, November or December? Build in a spare day around every boat, and keep the Andaman coast as your plan B.
Frequently asked questions about Thailand
February to April are the driest months with the calmest sea, and January is usually fine too. The summer months from May to August are also good, when the rest of southern Thailand is wet.
Avoid October to December if you want reliable sunshine, as that is the wettest period on the Gulf. In those months the Andaman islands such as Koh Lanta and Koh Lipe are the better choice.
Yes, but it falls later than in the rest of Thailand, around October to December, with November the wettest month. In the summer months Samui usually gets only short showers.
Neither is better, they suit different trips and have opposite seasons. Pick Phuket roughly November to April and Koh Samui roughly January to August.
Travellers who plan Koh Samui with Stippl most often stay three nights. Add more if you want to combine it with Koh Phangan or Koh Tao.
Ready to pick your month? Start a Stippl trip, drop in Koh Samui and the islands around it, and the app lays out your nights, boats and flights in one place. Free forever.
