The best time to visit Chiang Mai is from November to February during the winters, which is also known as the "cool season". During this time the average temperature ranges from 19 degrees to 25 degrees, which is just the perfect temperature to explore the city and its mountain ranges. These months are also the most popular season of Chiang Mai for a tourist.
August is the onset of the rainy season in Chiang Mai which goes on till October; this is the best time to avoid peak tourist season. You can easily explore its natural areas because they will be in full bloom. The accommodation charges also drop off during the rainy season. If you want to attend the world-famous Songkran Festival, then April will be an excellent time to visit.