Why the Gap Between IST and US Time Keeps Moving
India Standard Time is UTC+5:30 and never changes. The United States, by contrast, shifts most of its territory by an hour twice a year. That single asymmetry is the reason a meeting slot that worked in January is wrong in April.
| US zone | Standard (Nov–Mar) | Daylight (Mar–Nov) | Gap from IST |
|---|
| Eastern (New York) | UTC−5 | UTC−4 | 10h30 / 9h30 |
| Central (Chicago) | UTC−6 | UTC−5 | 11h30 / 10h30 |
| Mountain (Denver) | UTC−7 | UTC−6 | 12h30 / 11h30 |
| Pacific (Los Angeles) | UTC−8 | UTC−7 | 13h30 / 12h30 |
So 9:30 am in New York is 8:00 pm in Mumbai during American summer, and 7:00 pm during American winter. Anyone who memorised one of those and applied it year-round has, at some point, joined a call an hour late.
The Transition Dates Do Not Line Up
US daylight saving begins on the second Sunday in March and ends on the first Sunday in November. The European Union switches on the last Sunday in March and the last Sunday in October. That leaves two awkward windows each year — roughly three weeks in March and one week in late October — when the India-to-US gap and the India-to-Europe gap are both different from what they were a fortnight earlier, and different from each other. If you run calls across India, London and New York, those are the weeks things break.
Arizona, most of it, does not observe daylight saving at all, and neither does Hawaii. Puerto Rico and the US Virgin Islands stay on Atlantic Standard Time year-round. A colleague in Phoenix is on Mountain time in winter and effectively on Pacific time in summer, which catches out almost everybody.
The Half-Hour Offset
India's 30-minute offset means the gap to any US zone always ends in :30. This has a practical consequence for scheduling: there is no whole-hour slot that is a round number on both sides. A call at 9:00 am Eastern is 6:30 pm or 7:30 pm in India. If you want a round hour in India, you must accept a half-hour start in the US. Teams that fail to agree which side gets the round number tend to accumulate calendar drift.
Practical tip: never write a time without its zone, and prefer sending calendar invitations over typing times into a message. An invitation carries the underlying instant and each recipient's client renders it correctly in their own zone, including across daylight saving changes. A time typed into an email is just text, and text does not adjust.
A Realistic Overlap Window
Take an Indian team on roughly 10:00 to 19:00 IST and an Eastern-time team on 09:00 to 17:00.
- During US daylight time (gap 9h30): the US day starts at 18:30 IST. Overlap is 18:30 to 19:00 IST — thirty minutes, unless one side extends.
- During US standard time (gap 10h30): the US day starts at 19:30 IST, after the Indian day has ended. There is no overlap at all without someone shifting hours.
This is why India–US teams typically settle on a standing window of 19:00 to 21:00 IST, which is 08:30 to 10:30 Eastern in summer and 07:30 to 09:30 in winter, and then rotate the inconvenience rather than always imposing it on the same side.
Common Mistakes
Assuming "EST" means Eastern time year-round
EST specifically means the winter offset, UTC−5. From March to November the correct label is EDT, UTC−4. Writing "3pm EST" in July is technically an hour off from what the writer meant. Saying "Eastern time" or "New York time" avoids the problem entirely.
Forgetting that the date changes
Because the gap exceeds nine and a half hours, mid-morning in India is the previous evening in the United States. A 10:00 IST Monday slot is Sunday evening in New York. Late-evening Indian calls land on the correct day; morning ones frequently do not.
Scheduling across a transition weekend
A recurring meeting created before a switchover will move for one side. Recurring events are anchored to a specific zone, so whoever is not in that zone sees the local time shift. Check recurring series in mid-March and early November.
Ignoring public holidays
Thanksgiving, Independence Day on 4 July and the late-December period are largely dead weeks in the US, while Diwali, Holi and Republic Day are in India. Neither side's calendar shows the other's.
Converted In Your Browser
The conversion uses your browser's own time zone database, which is kept current by the operating system and handles daylight saving transitions and historical rule changes automatically. Nothing about the times you enter is transmitted anywhere. You can verify that by watching the Network panel in developer tools, or by disconnecting from the internet after the page has loaded and converting anyway.
More Questions Answered
What is the current difference between IST and New York time?
Nine and a half hours during US daylight saving, from the second Sunday in March to the first Sunday in November, and ten and a half hours for the rest of the year.
Why does the difference always end in thirty minutes?
India Standard Time is UTC+5:30, a half-hour offset. Since US zones sit on whole hours, the gap to any of them will always include an extra thirty minutes.
Is EST the same as Eastern time?
Not always. EST refers specifically to the winter offset of UTC−5. Between March and November the correct term is EDT, UTC−4. Saying Eastern time or naming the city avoids the ambiguity.
Does India observe daylight saving?
No. India has used a single fixed offset year-round since independence, so the difference changes only when the other country switches.
Which US states skip daylight saving?
Most of Arizona and all of Hawaii, plus territories including Puerto Rico and the US Virgin Islands. Phoenix effectively aligns with Mountain time in winter and Pacific time in summer.
When are the changeover dates?
The United States switches on the second Sunday in March and the first Sunday in November. Europe switches on the last Sunday in March and the last Sunday in October, so the two do not coincide.
What is the best way to avoid confusion?
Send calendar invitations rather than typing times into messages. An invitation stores the underlying instant and each recipient's calendar displays it correctly in their own zone.
Is the time data I enter sent anywhere?
No. Conversion uses the time zone database already present in your browser and runs entirely on your device.