The best time to visit Bangkok is from November to February. During these months, the weather is pleasant and dry, making it great for sightseeing without being bothered by the heat and humidity. However, Christmas and New Year’s eve can be crowded.
If you want to experience Thailand’s top festival, then come in April, which is the month for the Thai New Year (Songkran festival). May to October are best avoided due to the monsoon rains, but these are also the most affordable time to visit due to discounts.