Bangalore enjoys moderate climate throughout the year and one can visit this magnificent city at any time of the year with utmost ease. However, the months between September and February see the highest tourist inflow to the city because the weather becomes even more pleasant during the winter season. Here's a seasonal break-up so you can plan your trip better:
October to February: The winter months in Bangalore are the best time to visit the city. It doesn't really get very cold with the lowest temperature dipping to about 10°C. With so many lakes and gardens to visit, sightseeing and outdoor activities are most comfortable at this time. You wouldn't need heavy woolens but carry a light jacket, especially for the nights, which tend to get chilly. This is also a good time to plan getaways from Bangalore since there are a number of tourist attractions just outside Bangalore.
March to May: While winters are over, the temperature is still pleasant. The maximum temperature doesn't usually cross 36°C even in the hottest months making it perfect for the summers as well.
June to September: Monsoons begin by the end of May and come with mild to heavy rainfall. August and September can see heavy showers but they are rarely continuous so you can still plan a trip without the rain becoming a dampener. Just carry an umbrella and a sturdy pair of shoes, and you are good to go.