Kolkata is in India and is currently on UTC+5:30. Its time zone is Asia/Kolkata.
Kolkata does not observe daylight saving time. It stays on UTC+5:30 all year, so the difference to any other place that also holds a fixed offset never changes.
The weekend in Kolkata falls on Saturday and Sunday. A working day of 9:00 AM to 6:00 PM is the assumption used on the board.
Kolkata shares Asia/Kolkata with 7 other cities in the catalogue. They all read the same time and change their clocks together.
See the current time across India, including the other cities Meridian tracks there and the time zones they use.