Thailand has more than 1,400 islands, and choosing between them is the single hardest part of planning a trip here. The good news is that one fact narrows it down enormously – and most guides bury it: Thailand’s two coasts have opposite monsoon seasons. Get that right and you’ll have sunshine; get it wrong and you’ll spend your holiday watching cancelled ferries from a wet beach. Here’s how to pick the right island for your dates and your travel style.
The One Rule That Decides Everything
Thailand’s south splits into two coasts that trade weather across the year:
- The Andaman Coast (Phuket, Krabi, Koh Phi Phi, Koh Lanta, Koh Lipe) – dramatic limestone karsts and the best diving. Best November to April. Wettest May to October, peaking in September, when seas get rough and ferries are cancelled.
- The Gulf Coast (Koh Samui, Koh Phangan, Koh Tao) – calmer, gentler seas. Best January to August. Wettest October to December, with November the soggiest month of all on Samui.
The practical upshot: travelling in July or August? Choose the Gulf. Travelling in December to March? Either coast works, but the Andaman is more spectacular. Travelling in October or November? The Gulf is a gamble – the Andaman is drying out and is often the safer bet late in the season.
The Islands, and Who Each One Suits
Phuket – the all-rounder
Thailand’s biggest island, and the easiest to reach (its own international airport). Everything is here: resorts from budget to spectacular, nightlife in Patong, restaurants, and a launchpad for Phang Nga Bay and the Similans. It’s also the most crowded and developed. Best for: first-timers, short trips, families, anyone who wants convenience.
Krabi and Railay – the scenery
The mainland province opposite Phuket, and home to Thailand’s most dramatic landscape: the towering limestone cliffs of Railay and Phra Nang Cave Beach, reachable only by longtail boat. World-class rock climbing. Best for: scenery, climbers, couples, photographers.
Koh Phi Phi – stunning, and exhausting
Let’s be honest about this one. The cliffs and water are genuinely spectacular, and Maya Bay (from The Beach) is beautiful – but it’s a mass-tourism machine. Tonsai Bay is chaotic and overpriced, and Maya Bay is thick with boats. Best for: young party travellers. Otherwise: base at Koh Lanta or Railay and visit on a day trip, or skip it.
Koh Lanta – the quiet Andaman alternative
Long, laid-back beaches, an atmospheric old town, and easy access to superb diving. Far calmer than Phi Phi or Phuket. Best for: families, couples, slow travellers, divers.
Koh Samui – the polished Gulf resort island
The Gulf’s biggest name, with its own airport, high-end resorts along Chaweng and Lamai, night markets and reliable infrastructure. Less dramatic scenery than the Andaman, but comfortable and easy. Best for: resort holidays, honeymoons, digital nomads, long stays.
Koh Phangan – jungle and the Full Moon Party
Famous for the Full Moon Party on Haad Rin – but the north of the island is a completely different, quiet world of jungle and yoga retreats. Best for: partygoers and, on the far side, people escaping them.
Koh Tao – the divers’ island
The cheapest place in the world to get scuba-certified, with warm, clear, shallow water and a huge cluster of dive schools. Small, social and laid-back. Best for: divers and anyone wanting to learn.
The quieter picks
- Koh Lipe – far south in the Andaman, walkable, with startlingly clear water; sometimes called the Maldives of Thailand.
- Koh Chang, Koh Kood and Koh Mak – the eastern Gulf near the Cambodian border: jungly, mountainous, and far less touristed. (Note Koh Chang follows the Andaman-style pattern – best November to May.)
- The Trang islands (Koh Kradan, Koh Mook) – genuinely off the mass-tourism map.
Sample Island-Hopping Routes
- Andaman classic (10-12 days): Bangkok → Phuket → Koh Phi Phi → Krabi/Railay → Koh Lanta.
- Gulf classic (10-12 days): Bangkok → Koh Samui → Koh Phangan → Koh Tao. Easy ferries, one weather pattern, and diving plus beaches plus nightlife.
- Both coasts (2 weeks+): Phuket → Railay → fly to Koh Samui → Koh Phangan → Koh Tao. Needs one internal flight, but you see the best of each.
One warning: don’t cram five islands into ten days. Ferry transfers eat entire days, and you’ll spend the trip packing. Two or three islands is the sweet spot.
Practical Tips
- Airports save days. Phuket, Krabi and Koh Samui have their own; everywhere else means a ferry. If you’re short on time, start at one of the three.
- Book ferries ahead in peak season, and expect Andaman routes to be the first cancelled in bad weather.
- Green season is a real bargain – hotel rates can drop by up to half, and rain usually comes in short, sharp afternoon bursts rather than all day. Just pick the right coast.
- Pack strong repellent – dengue is a genuine risk, especially in the wetter months.
Conclusion
The best Thai island isn’t a fixed answer – it’s whichever one is sunny when you’re there and matches how you want to travel. Check your dates against the two monsoons first, then pick between Andaman drama and Gulf ease. For the mainland side of your trip, see our Bangkok travel guide and our Thailand travel guide.
FAQs
Which Thai island should I visit?
It depends on your dates. For November-April choose the Andaman (Phuket, Krabi, Koh Lanta); for May-September choose the Gulf (Koh Samui, Koh Phangan, Koh Tao). Then match the island to your style: Phuket for convenience, Krabi for scenery, Koh Tao for diving, Koh Lanta or Koh Samui for a relaxed beach stay.
When is the best time to visit the Thai islands?
December to March is the sweet spot when both coasts are generally good. The Andaman coast is best November-April; the Gulf coast is best January-August, with October and November its wettest months.
Is Koh Phi Phi worth visiting?
It’s spectacular but heavily over-touristed – Maya Bay is packed with boats and Tonsai is chaotic. It’s great if you want the party scene; otherwise, base yourself on Koh Lanta or at Railay and visit on a day trip.
Which Thai island is best for families?
Koh Lanta for calm beaches and a relaxed pace, or Koh Samui and Phuket for resort facilities and easy flights. Avoid Koh Phi Phi and Koh Phangan’s party areas.
Where should I learn to dive in Thailand?
Koh Tao – it’s the cheapest and most popular place in the world to get scuba-certified, with warm, calm, shallow water and dozens of dive schools.
How many islands should I visit in one trip?
Two or three. Ferry transfers can eat a whole day each, so cramming five islands into ten days means spending your holiday packing rather than on the beach.
