Understanding time zone offsets
The table lists the supported zones with their standard UTC offsets and daylight-saving behavior per the IANA time zone database. DST-observing zones spend part of the year one hour ahead of their standard offset.
| Zone (IANA name) | City label | Standard offset | Daylight saving |
|---|---|---|---|
| UTC | UTC | UTC+0 | None |
| Europe/London | London | UTC+0 (GMT) | UTC+1 (BST) in summer |
| Europe/Berlin | Berlin | UTC+1 (CET) | UTC+2 (CEST) in summer |
| Europe/Paris | Paris | UTC+1 (CET) | UTC+2 (CEST) in summer |
| Africa/Johannesburg | Johannesburg | UTC+2 (SAST) | None |
| America/New_York | New York | UTC−5 (EST) | UTC−4 (EDT) in summer |
| America/Chicago | Chicago | UTC−6 (CST) | UTC−5 (CDT) in summer |
| America/Denver | Denver | UTC−7 (MST) | UTC−6 (MDT) in summer |
| America/Los_Angeles | Los Angeles | UTC−8 (PST) | UTC−7 (PDT) in summer |
| America/Sao_Paulo | São Paulo | UTC−3 (BRT) | None (DST abolished 2019) |
| Asia/Dubai | Dubai | UTC+4 (GST) | None |
| Asia/Kolkata | Kolkata / Mumbai | UTC+5:30 (IST) | None |
| Asia/Shanghai | Shanghai / Beijing | UTC+8 (CST) | None |
| Asia/Tokyo | Tokyo | UTC+9 (JST) | None |
| Asia/Singapore | Singapore | UTC+8 (SGT) | None |
| Australia/Sydney | Sydney | UTC+10 (AEST) | UTC+11 (AEDT) in southern summer |
| Pacific/Auckland | Auckland | UTC+12 (NZST) | UTC+13 (NZDT) in southern summer |
- The conversion uses today's offsets from the IANA time zone data built into your browser, so daylight saving transitions are applied automatically without manual correction.
- Northern and southern hemispheres observe DST in opposite halves of the year, so the London-Sydney gap swings between 9 and 11 hours across the seasons.
- Some offsets are not whole hours — India (IST) is UTC+5:30, and a few zones elsewhere use +5:45 or half-hour offsets.
- Time zone rules change by government decision (São Paulo abolished DST in 2019); the IANA database is updated several times a year to track such changes.
What is a time zone conversion?
A time zone conversion translates a clock time in one region into the simultaneous clock time in another, by applying the difference between the two zones' UTC offsets. Every time zone is defined by its offset from Coordinated Universal Time (UTC) — Johannesburg is UTC+2 year-round, while New York is UTC−5 in winter and UTC−4 during daylight saving time.
Time zone rules are maintained in the IANA Time Zone Database (also called the tz database or zoneinfo), the reference data set used by operating systems and programming languages worldwide. Zones are named after representative cities — America/New_York, Asia/Tokyo — precisely because offsets and daylight-saving rules are set politically and change over time; the database records the full history and current rules for each region.
Daylight saving time is why the difference between two cities is not constant. London and New York are usually 5 hours apart, but for a few weeks each spring and autumn — when one has switched and the other has not — the gap is 4 hours. This converter computes both zones' offsets for today's date using the IANA data built into the browser, so DST is handled automatically without manual adjustment.
How to use this time zone converter
- Enter the time in 24-hour HH:MM format — for example 14:00.
- Select the source zone (where that clock time applies) from the 17 supported cities.
- Select the destination zone you want the equivalent time in.
- Read the converted time and the current offset difference; a (+1d) or (−1d) marker means the converted time falls on the next or previous day.
The formula behind time zone conversion
The converter determines each zone's current UTC offset from the IANA data for today's date, takes the difference, and adds it to the source time. Results wrap around the 24-hour clock, flagging a day shift when the sum passes midnight in either direction.
Worked example: 14:00 in London converted to Johannesburg during British Summer Time. London is UTC+1 (BST) and Johannesburg UTC+2 (SAST), so the difference is +1 hour and the result is 15:00. In winter the same conversion yields 16:00, because London reverts to UTC+0 while Johannesburg has no daylight saving.
Common mistakes
- Using a fixed hour difference year-round — DST-observing pairs like London-New York shift between 4 and 5 hours apart across the year.
- Forgetting the date can change — 20:00 in Los Angeles is already 13:00 the next day in Auckland; watch the (+1d) marker when scheduling.
- Assuming every zone is a whole hour from UTC — India runs at UTC+5:30, so New York to Mumbai is a 9.5- or 10.5-hour difference depending on US DST.
- Confusing zone abbreviations — 'CST' means Central Standard Time in Chicago but China Standard Time in Shanghai; IANA city names avoid the ambiguity.
- Scheduling near a DST transition without checking — meetings on the few days when only one side has switched are the classic missed-call scenario.
Häufig gestellte Fragen
How do I convert a time between two time zones?
Find each zone's current UTC offset, take the difference, and add it to the source time. For example, 14:00 in London (UTC+1 during British Summer Time) converted to Johannesburg (UTC+2 year-round) adds one hour, giving 15:00. This calculator does the lookup automatically using IANA time zone data, including daylight saving adjustments.
Does this converter handle daylight saving time?
Yes. Offsets are computed for today's date from the IANA time zone database built into your browser, which encodes each zone's daylight-saving rules. When London is on BST and New York on EDT the difference is 5 hours; during the brief spring and autumn windows when only one has switched, the correct 4-hour gap is applied automatically.
What is the IANA time zone database?
The IANA Time Zone Database (tz database or zoneinfo) is the reference compilation of time zone and daylight-saving rules for every region of the world, maintained by the Internet Assigned Numbers Authority. Zones are named after representative cities, such as America/New_York or Asia/Tokyo, and the database is updated several times a year as governments change their rules.
Why did my converted time show (+1d)?
The (+1d) marker means the converted time falls on the following calendar day. Converting 20:00 in Los Angeles to Tokyo adds 16 or 17 hours (depending on US daylight saving), landing at 12:00 or 13:00 the next day. Similarly (−1d) means the destination is still on the previous day.
Why is India's time zone offset not a whole hour?
India Standard Time runs at UTC+5:30 by national decision — offsets are political choices, not geographic necessities. Other non-whole-hour offsets exist too, such as Nepal at UTC+5:45 and parts of Australia at UTC+9:30. This is one reason time zone arithmetic should use real zone data rather than assumed whole-hour differences.
Why is the time difference between two cities not always the same?
Because daylight saving time starts and ends on different dates in different countries, and the hemispheres observe it in opposite seasons. London and Sydney are 11 hours apart in the southern summer, 9 hours apart in the northern summer, and 10 hours apart briefly in between. Zones without DST, such as Johannesburg, Dubai and Tokyo, keep a fixed offset from UTC year-round.
Quellenangaben
- IANA Time Zone Database (tz database) — the reference time zone and daylight-saving rules. iana.org/time-zones.
- ISO 8601 — Date and time — Representations for information interchange (UTC offsets). International Organization for Standardization.
- NIST — Time and Frequency Division: Coordinated Universal Time (UTC). nist.gov.