What is the best time of year to visit Thailand?

The best time to visit Thailand is from November to February, it's the cool season, it's not too hot and there's no rain.

This is also the high season.

March to April/May is the hot season.

However, the low season from May to October, which coincides with the rainy season, offers much cheaper accommodation.

With plenty of activities, festivals, shopping malls and markets, cultural venues and amusement parks to keep visitors entertained all year round, Thailand is the place where everyone can have fun at any time of the year.

And the climate is different in each region, from north to south.

You can find more details in this article:
When to go to Thailand: by region