IST offset: UTC+5:30
IST does not shift. No daylight saving, no seasonal clock changes, no exceptions. The offset stays UTC+5:30 every day of the year. The IANA representative zone is Asia/Kolkata. Sri Lanka (Asia/Colombo) uses the same offset but under a legally distinct standard.
The practical effect hits hardest when scheduling across the Atlantic. On 15 January 2026, New York is 10.5 hours behind IST. On 15 July 2026, that gap shrinks to 9.5 hours behind. The target zone moves. IST does not.
IST to all major time zones
Every offset below is relative to IST. A negative number means the zone is behind IST; a positive number means it is ahead. Where a zone observes DST, the summer offset appears in parentheses.
| Time zone | Standard offset from IST | DST offset from IST | DST observed? |
|---|---|---|---|
| New York (EST/EDT) | -10.5 hours | -9.5 hours | Yes |
| Los Angeles (PST/PDT) | -13.5 hours | -12.5 hours | Yes |
| Chicago (CST/CDT) | -11.5 hours | -10.5 hours | Yes |
| London (GMT/BST) | -5.5 hours | -4.5 hours | Yes |
| Paris (CET/CEST) | -4.5 hours | -3.5 hours | Yes |
| Dubai (GST) | -1.5 hours | -1.5 hours | No |
| Singapore (SGT) | +2.5 hours | +2.5 hours | No |
| Tokyo (JST) | +3.5 hours | +3.5 hours | No |
| Sydney (AEST/AEDT) | +5.5 hours | +4.5 hours | Yes |
| Johannesburg (SAST) | -3.5 hours | -3.5 hours | No |
| São Paulo (BRT/-) | -8.5 hours | -8.5 hours | No |
Why is India's time zone 30 minutes off?
IST sits on a half-hour offset because it was pegged to a single meridian: 82.5°E, passing through Mirzapur in Uttar Pradesh. Adopted on 1 January 1906, this longitude split the difference between Calcutta Time (UTC+5:53:20) and Bombay Time (UTC+4:51). The compromise stuck. After independence in 1947, India retained one national zone to reinforce political unity.
Other zones with non-standard offsets exist worldwide. Nepal runs 15 minutes ahead of IST at UTC+5:45. Iran sits at UTC+3:30, two hours behind IST. Afghanistan uses UTC+4:30, one hour behind. Myanmar is one hour ahead at UTC+6:30. Australian Central Time operates at UTC+9:30 standard, four hours ahead of IST, shifting to UTC+10:30 during its DST period.
The half-hour gap creates real friction. People doing mental math round to full hours and miss meetings by 30 minutes. The IST abbreviation itself compounds the problem: Irish Standard Time (UTC+1) and Israel Standard Time (UTC+2) share the same three letters but sit hours apart.
DST impact on IST conversions
IST never moves. The only variable in any conversion is whether the target zone is on standard time or daylight time.
For US zones, the difference shifts by exactly one hour between winter and summer. A 12:00 IST call with New York lands at 01:30 EST in January but 02:30 EDT in July. Los Angeles swings from 13.5 hours behind to 12.5 hours behind. Chicago moves from 11.5 hours behind to 10.5 hours behind.
For the UK and Europe, the same one-hour rule applies. London is 5.5 hours behind IST on GMT and 4.5 hours behind on BST. Paris shifts from 4.5 hours behind to 3.5 hours behind.
For zones without DST, the offset is constant. Dubai stays 1.5 hours behind. Singapore stays 2.5 hours ahead. Tokyo stays 3.5 hours ahead. Johannesburg stays 3.5 hours behind. São Paulo stays 8.5 hours behind.
Sydney inverts the pattern. Its summer (AEDT) runs during India's winter, so the gap shrinks: 5.5 hours ahead on AEST, 4.5 hours ahead on AEDT.
Recurring calls across DST boundaries break predictably. The US and Europe change clocks on different weekends. A slot that works in March can fail in April. Check the specific date.