IST sits at UTC+5:30 — one of the few half-hour timezones in the world. The reason is a compromise made over a century ago.
Standard timezones are based on meridians of longitude spaced 15° apart — each 15° equals one hour. India’s reference meridian, 82.5°E, passes near Mirzapur in Uttar Pradesh. It sits exactly halfway between the 75°E meridian (UTC+5) and the 90°E meridian (UTC+6). Halfway between the meridians means halfway between the hours: UTC+5:30.
In the 1800s, British India ran on multiple local times. The two most important were Bombay Time (about UTC+4:51) and Calcutta Time (about UTC+5:54). Railways and telegraphs made this chaos untenable — a train schedule meant different clock times in different cities.
Indian Standard Time at UTC+5:30 was adopted in the early 1900s as a single national compromise between the western and eastern extremes. Calcutta Time held on until 1948, and Bombay Time wasn’t fully retired until 1955 — decades of two clocks running in parallel.
India spans roughly 68°E to 97°E — nearly 30° of longitude, or two full hours of solar time. Picking UTC+5 would make sunrise painfully late in the northeast; UTC+6 would make it very early in the west. The +5:30 midpoint splits the difference so no region is more than about an hour from its natural solar time.
| Region | Offset |
|---|---|
| India, Sri Lanka | UTC+5:30 |
| Iran | UTC+3:30 |
| Afghanistan | UTC+4:30 |
| Myanmar | UTC+6:30 |
| Newfoundland (Canada) | UTC-3:30 |
| Nepal | UTC+5:45 |
Nepal goes even further with a 45-minute offset — IST is far from the strangest clock in the region.
The half-hour offset is why US–India time math never lands on round numbers: 9:00 AM EST is 7:30 PM IST, and 9:00 AM PST is 10:30 PM IST. Use our EST to IST converter or the meeting planner instead of doing the arithmetic in your head.
Indian Standard Time is based on the 82.5°E meridian, which lies exactly halfway between the UTC+5 and UTC+6 meridians. The midpoint produces a half-hour offset: UTC+5:30.
Yes. Before IST, Bombay Time (about UTC+4:51) and Calcutta Time (about UTC+5:54) were widely used. Bombay Time survived alongside IST until 1955.
No. India used DST briefly during wartime in the 20th century but has not observed it since. IST stays at UTC+5:30 all year.