How Mumbai, Kolkata & Chennai Followed Separate Time Zones Before Indian Standard Time Was Adopted

Before India embraced a single time zone, its major cities operated on distinct local times. Mumbai, Kolkata and Chennai each had their own clocks, calibrated to their geographic locations. This changed in 1906 with the adoption of Indian Standard Time (IST), creating a unified national time system. However, the journey to this synchronisation involved multiple shifts, including wartime time changes and the influence of colonial railways. Here's a closer look at how India moved from multiple local times to IST.

Cities With Their Own Clocks

Before Indian Standard Time was officially adopted, major Indian cities like Mumbai (then Bombay), Kolkata (then Calcutta) and Chennai (then Madras) followed their own local times. These time standards were based on the longitude of each city. For instance, Bombay Time operated at UTC+04:51, Calcutta Time at UTC+05:53:20, and Madras Time at UTC+05:21:14. This lack of uniformity posed significant challenges, especially for the growing railway and communication networks during British rule.

Madras Time And The Railways

Introduced in 1802, Madras Time was one of the earliest time standards in colonial India and served mainly the southern part of the country. It became known as "Railway Time" due to its widespread use on railway timetables and schedules. While it served logistical purposes well in the south, it didn’t align with timings in other regions, leading to confusion as travel and trade expanded across the subcontinent.

Calcutta And Bombay Maintained Local Time

Even after a unified IST was introduced, Kolkata and Mumbai continued to use their local time for several more years. Calcutta Time was used officially until 1948, and Bombay Time persisted until as late as 1955. This dual-time practice was common in everyday life. Newspapers, government offices and radio broadcasts often mentioned both the local and Indian Standard Time, illustrating the slow transition towards a single national standard.

The Shift To Indian Standard Time

India formally adopted IST on 1 January 1906, during the British Raj. It was based on the 82°30' E longitude, which passes near Mirzapur in Uttar Pradesh. This longitude was chosen as it lies roughly midway between the western and eastern parts of the country. The decision aimed to strike a balance between the varying solar times across India and bring consistency to national affairs such as transport, administration and communication.

Post-Independence Time Standardisation

After India gained Independence in 1947, IST was reaffirmed as the official time for the Republic of India. However, the usage of city-specific times lingered. It wasn’t until the late 1940s and 1950s that local time zones were phased out completely. The central observatory responsible for maintaining IST was moved from Chennai to Shankargarh Fort in Allahabad (now Prayagraj) to be closer to the standard meridian.

Wartime Use Of Daylight Saving

While India currently does not observe Daylight Saving Time, it was implemented briefly during specific wartime periods. In 1962 during the China–India War, and again in 1965 and 1971 during the Indo-Pakistan Wars, clocks were adjusted as a temporary measure to conserve energy. However, these shifts were short-lived and never adopted permanently.

Calculating IST

IST is calculated from the 82°30' E longitude, and its official time is maintained today by the National Physical Laboratory of India in New Delhi. The decision to base IST on this central meridian helps maintain a uniform time offset of UTC+05:30 throughout the country, regardless of geographic differences in sunrise and sunset times between the eastern and western regions.

Time In The Northeast

There have been ongoing discussions about introducing a separate time zone for India’s northeast, where sunrise and sunset occur earlier compared to the rest of the country. Some experts argue that a second time zone could improve productivity and energy efficiency, but no official steps have been taken so far.