Thailand Islands Guide: Which Ones to Visit and When

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Thailand’s islands split across two coasts that don’t share a calendar — the single most useful fact for planning an island trip here, and one that trips up more first-time visitors than almost anything else in the itinerary. Which island is “best” depends heavily on what you actually want from it and, just as much, on which month you’re going. This guide covers both: the six main islands worth knowing about, what each one is actually for, and the timing logic that decides when to visit which coast.

The Two Coasts: Andaman Sea vs Gulf of Thailand

Phuket, Krabi/Railay, and Koh Phi Phi sit on the Andaman Sea, on Thailand’s west side. Koh Samui, Koh Phangan, and Koh Tao sit on the Gulf of Thailand, on the east side. The two coasts face opposite monsoon patterns rather than sharing one: the Andaman side’s rainy season runs roughly May through October, while the Gulf side stays comparatively dry through most of that window and instead gets its wettest weather from October through December, with November typically the wettest month of the year on Koh Samui and Koh Phangan specifically. That means “the best time to visit Thailand’s islands” doesn’t have one answer — it depends entirely on which coast you’re headed to.

There’s one genuine overlap worth knowing: roughly January through March is dry season on both coasts at once, which is the one window where visiting islands on both sides of the country in a single trip makes the most sense without either leg landing in bad weather. Outside that window, picking a coast and matching your dates to it specifically will get noticeably better weather than trying to split the difference.

Which Island Fits Which Traveler

Easiest logistics for a first trip: Phuket and Koh Samui both have direct international airports, which matters more than people expect when you’re already managing jet lag and a new country. Best for diving: Koh Tao, hands down — see our Koh Tao diving guide for sites and schools, with the Similan Islands off Phuket as the Andaman side’s answer for a serious dive trip. Best for nightlife: Koh Phangan around a Full Moon Party date, or Phuket’s Patong strip year-round. Best for dramatic scenery and rock climbing: Krabi and Railay, where the limestone cliffs are the whole point of going. Best for families: Koh Samui’s calmer beaches or Phuket’s Kata and Karon areas, both with a wider range of family-oriented resorts than the smaller islands offer. Best for a tight budget: Koh Tao and the quieter parts of Koh Phangan away from Haad Rin, where prices run noticeably below Phuket or Koh Samui at every tier.

Phuket

Phuket is the default choice for a reason — it has the most direct flight connections, the widest range of hotels and neighborhoods, and enough non-beach activities (temples, viewpoints, day trips) that it works even for travelers who get restless after a few beach days. It’s also Thailand’s most-visited island, so expect more crowds and more development than anywhere else on this list. Full guide: Phuket travel guide. If you’re torn between Phuket and a Gulf island, see our Phuket vs Koh Samui comparison.

Krabi and Railay

Krabi trades some of Phuket’s convenience for genuinely more striking scenery — the limestone karsts rising straight out of the water are the reason climbers and photographers pick this over Phuket specifically. Railay itself is only reachable by longtail boat, which keeps it noticeably quieter than anywhere with road access. Full guides: Krabi and Railay Beach. See Krabi vs Railay and Krabi vs Phuket if you’re deciding between these specifically.

Koh Phi Phi

Small enough to see on foot, and built almost entirely around a handful of genuinely stunning viewpoints and the Maya Bay cove made famous by film. It gets heavy day-tripper traffic from Phuket and Krabi, so staying overnight — even just one night — buys real breathing room once the day-trip boats leave in the late afternoon. Full guide: Koh Phi Phi travel guide.

Koh Samui

The most developed island on the Gulf side, with its own international airport and a noticeably more polished, family-friendly feel than either Koh Phangan or Koh Tao. It’s the natural pick if you want a Gulf-coast trip without connecting through Bangkok or dealing with a ferry as your only way in. Full guide: Koh Samui travel guide.

Koh Phangan

Koh Phangan runs two genuinely separate identities depending on where you stay: Haad Rin, home to the monthly Full Moon Party, versus the rest of the island, which has quietly become one of Thailand’s biggest yoga and wellness destinations. Picking the wrong side of that split for what you actually want is the most common mistake travelers make here. Full guide: Koh Phangan travel guide.

Koh Tao

The smallest and most laid-back of the three Gulf islands, and priced accordingly — it’s built almost entirely around its dive schools and reefs, with far less in the way of nightlife or resort infrastructure than Koh Samui or Koh Phangan. Full guide: Koh Tao travel guide. See Koh Phangan vs Koh Tao vs Koh Samui for a direct comparison of all three.

Getting Between Islands

Within a coast, moving between islands is usually a straightforward ferry ride rather than a full travel day. On the Andaman side, Phuket connects to Koh Phi Phi by ferry in under two hours, and Phuket to Krabi is a straightforward road or ferry connection depending on which part of Krabi you’re headed to. Crossing coasts is the part that takes real planning — Phuket to Koh Samui, for instance, runs through a flight connection or a long ferry-and-bus combination rather than a direct hop, which is the practical version of the two-coasts split described above.

Can You Do Both Coasts in One Trip?

Yes, but it costs a full travel day each way, usually routed through Bangkok, so it’s worth doing only if you have at least ten days free for the islands portion alone. Our 2-week Thailand itinerary sticks to the Andaman side (Krabi and Koh Phi Phi) for exactly this reason — adding the Gulf side on top of that route would mean cutting time from the north to make room for the extra transfer days. If islands are the whole point of your trip rather than one stop among several, picking a single coast and going deeper on it usually beats trying to cover both.

Budgeting for an Island Trip

Hotel prices vary as much between islands as they do between mainland regions — Koh Samui and Phuket sit at the top of the range, while Koh Tao and Koh Phangan run noticeably cheaper at every tier. See our region-by-region hotel price guide for the full breakdown before you book.

Frequently Asked Questions

Which Thailand island should a first-timer visit?

Phuket or Koh Samui, since both have direct international airports and the widest range of hotels and activities. They’re also the easiest to fall back on if plans change once you’re there.

Do the Andaman and Gulf islands really have different weather seasons?

Yes — the Andaman side (Phuket, Krabi, Koh Phi Phi) is wettest roughly May through October, while the Gulf side (Koh Samui, Koh Phangan, Koh Tao) is wettest October through December, with November typically the worst month there specifically.

Is the Full Moon Party worth planning a trip around?

If nightlife is genuinely your priority, yes — it’s a real, singular experience. If it isn’t, it’s easy to avoid simply by staying away from Haad Rin on the relevant dates and enjoying the rest of Koh Phangan’s quieter side instead.

Which island has the best diving?

Koh Tao on the Gulf side and the Similan Islands off Phuket on the Andaman side are the two clearest answers, though they’re reached very differently and rarely combined into a single trip.