Temperature and rainy days: 1991–2020 climate averages for the Chiang Mai, Bangkok, Ko Samui and Phuket weather stations (station tables for Chiang Mai, Bangkok, Ko Samui and Phuket). Air quality is an approximate typical US AQI, and it changes a lot from year to year, so check live readings on IQAir before you go.

1. Northern Thailand — culture, cool air, and one important caveat

View Northern Thailand on the map

If your idea of a perfect trip involves cool mountain mornings, ancient Lanna temples, and jungle treks with local guides, the North is the most compelling choice in Thailand. Chiang Mai sits at around 300 metres elevation and is noticeably cooler than the coast from November through January, making it the best antidote to Bangkok’s relentless heat.

The caveat is real and worth taking seriously: from February through April, agricultural burning across the region causes air quality to deteriorate significantly. AQI readings above 150 (unhealthy) are common in March and April. If you have any respiratory sensitivity — or simply don’t want to spend your holiday indoors — avoid the North during this window. The planner scores this heavily when you select “I’m sensitive to bad air.”

For those who can visit in the right months, Chiang Mai’s hidden gems reward anyone willing to venture past the old city square. And the wider region — Pai, Chiang Rai, Nan — offers Northern Thailand hidden gems that most package tourists never find.

2. Bangkok & Central Thailand — urban energy, with an April asterisk

View Bangkok & Central Thailand on the map

Bangkok works almost year-round for most travelers, which is why it scores consistently in the planner even in “imperfect” months. The city’s street food, temples, markets, and rooftop bars are compelling at any time — but the experience changes significantly by season.

November through February is the sweet spot: crowds are high but so is the energy, temperatures are manageable (31–33°C), and the rain is minimal. April is the trickiest month — Songkran (Thai New Year, April 13–15) brings enormous domestic travel and the hottest temperatures of the year, often hitting 36°C. If you love chaos and water fights, it’s unmissable. If you don’t, plan carefully.

Bangkok’s biggest underrated asset is its role as a launch pad. Off-the-beaten-path Bangkok neighborhoods like Bang Krachao and Talat Noi offer canal-side calm minutes from the centre. And day trips from Bangkok to Ayutthaya, Kanchanaburi, or the coast make it easy to balance city intensity with breathing room.

3. The southern coasts — and why Gulf vs Andaman matters enormously

The single most important thing to understand about southern Thailand is that the Gulf Coast (Koh Samui, Koh Phangan, Koh Tao) and the Andaman Coast (Phuket, Krabi, Koh Lanta) operate on opposite monsoon cycles. When one side is sunny, the other is often wet. The planner treats them as separate regions specifically because of this.

Andaman Coast peaks November through April — the dry season brings flat seas perfect for diving and island-hopping. May through October is genuine monsoon season; many smaller operators and some islands close entirely. If you’re visiting purely for diving or snorkelling, this is the side that delivers world-class conditions when it’s dry. View the Andaman Coast on the map.

Gulf Coast follows the opposite pattern. January through August tends to be sunnier on this side, while October and November see its heaviest rainfall. Koh Samui has a very different calendar to Phuket, which many travelers only realize once they’re there. View the Gulf Coast Islands on the map.

Both sides benefit from excellent air quality year-round — a major advantage over the North during burning season. If respiratory health is a priority, the South is reliably the safest choice regardless of month. For something genuinely off the beaten path, a Koh Kood itinerary takes you to one of the last largely undeveloped islands on the Gulf side — thin crowds, pristine water, and air that stays clean all year.

Smart planning: what the planner won’t tell you on its own

The tool ranks regions — but the best Thailand trips often combine two. A common structure that works well: fly into Bangkok for 3–4 days, then head either North (if November–January) or South (if any time of year, matched to the right coast). This spreads your experience across very different environments without losing too many days to transit.

Before locking in flights, always cross-reference official regional forecasts on the Thai Meteorological Department website, and check current AQI readings on IQAir if the North is on your shortlist during Q1.

Once your region is set, pair it with our Thailand Trip Budget Calculator to get realistic cost estimates for accommodation, food, and transport across different travel styles.