When to Go
Low Season: The hottest weather arrives in April and grows increasingly stifling through June, when the monsoon season begins. This runs through mid-September and cools Kolkata down, though the occasional downpour means you can expect a soaking or two.
Shoulder Season: After the monsoon, it's festival time. The biggest of all festivals is the Durga Puja, which takes place over two weeks in September or October. All of West Bengal virtually shuts down for four days; getting around may be difficult.
High Season: Around December the mild winter sets in and lasts until March. This is the best time to visit, but as a result making advance reservations for hotels, trains, and airplanes is essential. The annual book fair and several open-air, all-night music concerts featuring classical, jazz, and rock musicians enliven this time. If you visit around Christmas, you're likely to see such tangible signs of the season as Christmas lights and fruitcake-like puddings. The town of Shantiniketan has its major festival, the Poush Mela, around the same time.