The EST–IST gap is 10.5 hours in January and 9.5 in July
These are the conversions people look up most often. Each one uses the calculator above with live data, so the offset shown always reflects whether daylight saving is currently in effect — unlike a printed conversion chart.
- EST to IST — US Eastern Time to India Standard Time, typically 10.5 hours apart in winter (EST) and 9.5 hours in summer (EDT), since India does not observe daylight saving.
- IST to EST/PST (India to USA) — India Standard Time is a single, fixed offset (UTC+05:30) year-round, so the gap to any US zone shifts by an hour whenever the US zone changes for daylight saving.
- IST to GMT/BST (India to UK) — 5.5 hours in UK winter, 4.5 hours in UK summer (BST).
- UTC / GMT / Zulu time — UTC never shifts for daylight saving; “Zulu” is aviation/military shorthand for the exact same instant as UTC.
- CET to GMT — Central European Time is normally 1 hour ahead of UK time, in both the winter and summer halves of the year, because both regions shift their clocks on close to the same dates.
- US Eastern to Amsterdam — a steady 6-hour gap year-round: Amsterdam is 6 hours ahead of US Eastern in both halves of the year, because the Netherlands and the US East Coast both shift their clocks, just on slightly different dates. 2:00 AM in New York is 8:00 AM in Amsterdam.
- Hong Kong to the UK — 8 hours in UK winter, 7 hours in UK summer. Hong Kong Time is a fixed UTC+08:00 with no daylight saving, so the whole change comes from the UK side moving to BST.
Standard time vs daylight time. Most abbreviations come in pairs: the standard one is the zone’s base offset, used in the winter half of the year, and the daylight one is that offset plus an hour, used in the summer half. EST (UTC−05:00) becomes EDT (UTC−04:00); CST becomes CDT; GMT becomes BST; CET becomes CEST. Which one applies depends on the date, not on the zone alone — so a conversion that is correct in January can be an hour wrong in July. Several zones never shift at all, including India Standard Time (UTC+05:30), Hong Kong Time (UTC+08:00), Japan Standard Time (UTC+09:00) and UTC itself. The calculator above looks up the offset for the specific date you enter rather than assuming a fixed one.
Which side of the pair actually moves. EST (Eastern Standard Time, UTC−05:00) covers the US East Coast and shifts to EDT (UTC−04:00) in summer. IST (India Standard Time, UTC+05:30) covers all of India and does not observe DST. CET (Central European Time, UTC+01:00) covers most of continental Europe and shifts to CEST (UTC+02:00) in summer. PST (Pacific Standard Time, UTC−08:00) covers the US West Coast and shifts to PDT (UTC−07:00) in summer. The converter shows the exact abbreviation and offset in effect for whatever date you enter, not just the standard-time label — so in an India-to-US pair only the US side ever moves. India is typically 9.5 hours ahead of US Eastern Time (10.5 hours ahead of EST in winter, 9.5 ahead of EDT in summer) and 12.5–13.5 hours ahead of US Pacific Time; against the UK it is 5.5 hours ahead of GMT (UTC+00:00) and 4.5 hours ahead of BST (UTC+01:00). Use the “IST to EST”, “IST to PST” and “IST to GMT/BST” quick-select buttons above for the exact current difference. India has not observed DST since a brief wartime experiment in 1942–45: it uses a single time zone across the whole country, and because it spans a relatively narrow range of longitudes north-to-south compared with its east-west spread, the practical benefit of shifting clocks seasonally is smaller than in higher-latitude countries, so IST has stayed fixed year-round since.
Why 1900 UTC and 7:00 PM UTC are one time, and CST is two
24-hour and UTC-offset notation. Times written as 1900 UTC, 18:00 UTC or 2:00 UTC−7 are the same thing as a 12-hour clock time, just written without AM/PM. 1900 UTC is 7:00 PM UTC. A trailing offset like UTC−7 or UTC+05:30 names the zone directly instead of by abbreviation, which avoids the ambiguity of letter codes — CST, for instance, is used for both US Central Standard Time (UTC−06:00) and China Standard Time (UTC+08:00). Enter either form above and the converter resolves it to a single instant before re-expressing it in every zone you add.
UTC, GMT and Zulu are not quite interchangeable. UTC (Coordinated Universal Time) is the modern time standard the world’s clocks are set against — it never changes for daylight saving. GMT (Greenwich Mean Time) is, in practice, the same instant as UTC almost all of the time, but GMT is also the name of the UK’s own time zone, which shifts to BST (UTC+1) every summer. So “UTC” and “the current UK time zone” are only identical for part of the year — this calculator treats UTC as fixed and lets you pick “Europe/London” separately if you specifically want UK local time. Zulu time is aviation, military, and maritime shorthand for UTC, written with a “Z” suffix (e.g. 14:00Z); it is exactly the same instant as UTC, so choosing “UTC” in this converter gives you Zulu time.
Never convert from an abbreviation alone. Time zone abbreviations are not globally unique. “CST”, for example, is used for US Central Standard Time (UTC−06:00) and also for China Standard Time (UTC+08:00) — a 14-hour difference for the same three letters. Because of this ambiguity, this calculator always shows the full UTC offset next to any abbreviation, and the underlying conversion always uses an unambiguous IANA zone identifier (like America/Chicago or Asia/Shanghai), never the abbreviation alone.
Military time and timestamp codes. This calculator already displays times in 24-hour format (e.g. 14:00 rather than 2:00 PM), which is what “military time” refers to — but a dedicated military-time tool for converting a specific 12-hour clock time to 24-hour notation, without also changing time zones, is planned separately for cases where no zone conversion is needed at all. Machine timestamp formats are the same story: this page converts a human date and time between time zones, and a dedicated Unix timestamp / Discord timestamp converter (for generating Discord’s <t:…> message-formatting codes) is planned as a separate tool. This page is the right one for “what time is it there” and scheduling-style conversions.
Subtract the offset once, add it back once per zone
Converting a time between zones takes two steps: first, turn the date/time you typed — as observed in the zone you say it’s in — into a single, unambiguous instant (this is what computers store internally, usually as a count of seconds since 1 January 1970 UTC). Second, re-express that same instant as a wall-clock date and time in each target zone. The same two steps plan a meeting across zones: fix one instant, then read it in each zone. In January, a 9:00 AM call in New York is 2:00 PM in London and 7:30 PM in Mumbai.
This calculator does not hard-code any zone’s offset or DST start/end dates. Both steps ask the browser’s built-in Intl time zone API, which is backed by the IANA Time Zone Database (see Sources) — the same database used by Linux, macOS, Windows, Android, and iOS. That is a deliberate choice: a hand-maintained offset table would silently go wrong the next time any country changes its DST rules, which happens most years somewhere in the world.
What that buys you at a DST boundary. Many zones — most of the US, Canada, the UK, and the EU, for example — shift their clocks forward about an hour in spring and back in autumn. Because the offset is fetched for the exact date and time you entered rather than read from a fixed table, daylight saving is handled automatically, including on dates whose offset differs from today’s. Nothing about zone rules or DST dates is hand-maintained on this page, so there is no static table to go stale: the Intl API is backed by the IANA Time Zone Database, the same dataset used by nearly every operating system, and it updates when your browser or OS updates.
Historical and future dates. The same lookup runs backwards and forwards, within the range your browser’s time zone database covers — typically many decades in each direction. Keep in mind that some countries have changed their time zone rules, DST start/end dates, or even their standard offset over the years; the calculator applies whatever rule was or will be in effect for the date you enter, according to the current IANA database, which is the same standard historians and software worldwide rely on.
When 19:00 UTC lands on tomorrow’s date in Mumbai
Reading a time across zones
On 15 January 2026 (northern-hemisphere winter), it’s 2:00 PM in New York — Eastern Standard Time, UTC−05:00, not observing daylight saving on this date. Step 1: 14:00 − (−05:00) = 19:00 UTC. Step 2, re-expressed: London is on GMT in January (UTC+00:00), so it’s also 19:00 there; Mumbai is on IST (UTC+05:30) year-round, so 19:00 + 05:30 = 00:30 the next day — this is exactly the kind of cross-midnight case the calculator flags with a “+1 day” marker.
Scheduling a call
You want to schedule a call for 9:00 AM Pacific Time (Los Angeles) on a date when the US is observing standard time (PST, UTC−08:00). Step 1: 09:00 − (−08:00) = 17:00 UTC. Step 2: Berlin is on CET in winter (UTC+01:00), so 17:00 + 01:00 = 18:00 the same day; Tokyo does not observe daylight saving (JST, UTC+09:00 year-round), so 17:00 + 09:00 = 02:00 the next day — worth double-checking with your Tokyo colleagues before you book the room.
Reading the +1 day and −1 day markers. They appear because the time difference plus the hour you entered pushes the converted time past midnight into the next calendar day, or back before midnight into the previous day, in that zone. The marker tells you the converted time is correct but falls on a different date than the one you entered — a common source of scheduling mistakes if it’s missed.
Five of these thirteen zones never move their clocks
UTC/GMT, India, the Gulf, China and Japan hold one offset all year; the other eight switch twice. Standard-time offsets for commonly searched zones are below. The live calculator above always computes the exact, currently-correct offset for the date you enter — this table is a quick static reference, so it clearly separates each zone’s standard-time offset from its daylight-saving offset rather than picking one and letting it go stale for half the year.
Common time zones with standard and daylight-saving UTC offsets| Zone | Standard time | Daylight saving |
|---|
| UTC / GMT | UTC±00:00 | Does not observe DST |
|---|
| US Eastern (New York) | EST, UTC−05:00 | EDT, UTC−04:00 |
|---|
| US Central (Chicago) | CST, UTC−06:00 | CDT, UTC−05:00 |
|---|
| US Mountain (Denver) | MST, UTC−07:00 | MDT, UTC−06:00 |
|---|
| US Pacific (Los Angeles) | PST, UTC−08:00 | PDT, UTC−07:00 |
|---|
| UK (London) | GMT, UTC+00:00 | BST, UTC+01:00 |
|---|
| Central Europe (Paris, Berlin) | CET, UTC+01:00 | CEST, UTC+02:00 |
|---|
| India (Kolkata) | IST, UTC+05:30 | Does not observe DST |
|---|
| Gulf (Dubai) | GST, UTC+04:00 | Does not observe DST |
|---|
| China (Shanghai) | CST, UTC+08:00 | Does not observe DST |
|---|
| Japan (Tokyo) | JST, UTC+09:00 | Does not observe DST |
|---|
| Australia Eastern (Sydney) | AEST, UTC+10:00 | AEDT, UTC+11:00 (Oct–Apr, opposite hemisphere) |
|---|
| New Zealand (Auckland) | NZST, UTC+12:00 | NZDT, UTC+13:00 (Sep–Apr, opposite hemisphere) |
|---|
The hour that happens twice and the hour that never happens
Five limitations can still make a converted time wrong, and the last one is on your side of the screen.
- Ambiguous and skipped local times near a DST transition. On the day clocks move back, one local hour occurs twice; on the day they move forward, one local hour never occurs at all. This calculator resolves those edge cases automatically using the same logic as your operating system, but a manually-entered time that technically doesn’t exist (e.g. 2:30 AM on a “spring forward” day in a zone that skips it) will be interpreted as the nearest valid instant rather than rejected.
- Depends on an up-to-date device. This calculator reads your browser’s copy of the IANA Time Zone Database. When a country changes its DST rules or standard offset with little notice, there can be a short window before browsers and operating systems ship the update — during that window, dates in the affected zone could be off by an hour, because a converter cannot know a rule the database has not shipped yet.
- No leap-second handling. Like virtually all consumer software, this tool works in civil (UTC) time and does not model the occasional leap second added to keep UTC aligned with the Earth’s rotation — irrelevant for everyday scheduling, but worth knowing for scientific timing use.
- Zone abbreviations are for display only. As covered above, the same three-letter abbreviation can mean different offsets in different countries — the calculator’s actual conversion always uses an unambiguous IANA zone identifier, never the abbreviation.
- Your device supplies the starting point. On load the converter reads your device’s own time zone setting and current time as the starting point, which you can then change to any zone and any date/time. If your device’s time zone or clock is set incorrectly, that starting point will be off, so it is worth checking your device settings if the auto-filled time looks wrong.
Sources and methodology
Zone and DST data: this calculator does not maintain its own offset table. Every conversion is computed live from the browser’s built-in time zone database, which implements the IANA Time Zone Database (also called tz database or zoneinfo) — the authoritative source used by nearly every operating system and programming language worldwide.
Instant resolution: the two-step wall-time ↔ UTC-instant method described in the two-step method above is the standard approach used by time zone libraries generally, not a bespoke algorithm.