The best time to visit Kolkata is between November to mid-March. This is the dry season which coincides with lower temperatures (12°C to 29°C). It is also peak tourist season, so booking rooms and travel tickets in advance is advisable.
Winter Season:
Winter is probably the most awaited season in Kolkata. The winter months in Kolkatta are December to February. The temperature in winter sinks down to 13°C at this time. With pleasant days and cool mornings, winter is the most preferred season in this city. In these 3 months, you can enjoy lots of music festivals are on and different fairs and various craft and handloom exhibitions (Saras Mela, Bidhannagar Mela, Book Fair, etc) to see and even buy the latest traditional and local artwork. Spend Christmas in Park Street and experience the grand celebration.
Summer Season:
The summer season extends from first week of March to June. While summer in this region is noted for excessive humidity. The city of Joy normally known as a Summer city, which has different kinds of summer weather like Sweaty summer, rainy summer, sweaty and rainy summer, breezy summer and chilled summer. Temperature in Kolkata is usually around 41°C. During summer you can enjoy the festival like Poila Boishakh, Jamai Shashti.
Monsoon Season:
June to September is monsoon season in Kolkata. The climate remains wet throughout as the town receives around 1582m average rainfall. Monsoon months are blessed with heavy rainfall. Major festivals in Kolkata are Durga Puja (the city is known all around the world for its famous Durga puja celebrations. Pooja is conducted in the month of September/October, this is known as the best time to see city of Joy) & Kali Puja (Kali puja celebrate after Durga Puja is again one of the biggest festivals in Kolkata). The city is very enthusiastic & active during this festive period where you can enjoy culture & Cuisine.