epochkit

Timezone Converter

View a single moment across multiple timezones side by side. IANA-based, DST-aware, and saved across sessions.

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How to use

  1. 1

    Set a reference time

    Enter any date and time in the input above and choose the timezone you're working from. All rows update instantly.

  2. 2

    Add or remove timezones

    Click "Add timezone" to add a row (up to 6). Use the dropdown on each row to pick any IANA timezone. Click × to remove a row.

  3. 3

    Your list is saved

    Your timezone selection persists via localStorage. Reopen the page and your preferred zones are already loaded.

About timezone conversion

Every timezone in this tool is drawn from the IANA Time Zone Database (also called the tz database or Olson database), the authoritative, community-maintained record of all world timezones. It powers timezone support in Linux, macOS, Java, Python, Go, PostgreSQL, and most modern programming environments. IANA identifiers follow the Region/City format — for example America/New_York or Asia/Kolkata — and are the safest choice in any API or database field.

Daylight Saving Time (DST) is handled automatically. The IANA database encodes every historical and future DST transition, so you never need to add or subtract an hour manually. When you pick a date in summer versus winter, the converter reflects the correct UTC offset for that exact moment — including edge cases like the spring-forward and fall-back hours.

Developers often confuse UTC, GMT, and Z. For practical purposes they all mean UTC+0, but UTC is the precise scientific standard; GMT is the historical mean solar time at the Greenwich meridian; and Z (Zulu) is the ISO 8601 and military shorthand for UTC+0. When writing timestamps in API responses, append Z (e.g., 2026-05-09T18:00:00Z) or include an explicit offset like -07:00.

A safe rule of thumb for distributed systems: store in UTC, display in the user's local timezone. UTC timestamps are unambiguous, sortable, and unaffected by DST transitions. Convert to local time only at the display layer. This converter lets you verify that your conversion logic produces the expected output across any combination of zones before you ship.

Frequently asked questions

Why does epochkit use "America/New_York" instead of "EST" or "ET"?
Abbreviations like EST, IST, or CST are ambiguous — EST could mean Eastern Standard Time (UTC−5) or Australian Eastern Standard Time (UTC+10). IANA timezone identifiers like "America/New_York" are unambiguous, encode DST rules automatically, and are the standard used by all major programming languages and operating systems.
Does the converter handle Daylight Saving Time automatically?
Yes. IANA timezone rules include all historical and current DST transitions. When you pick "America/New_York", the converter automatically applies UTC−5 in winter (EST) and UTC−4 in summer (EDT) based on the exact date and time you enter. No manual adjustment needed.
What is the difference between UTC, GMT, and Z?
UTC (Coordinated Universal Time) is the modern international time standard. GMT (Greenwich Mean Time) refers to the mean solar time at the Greenwich meridian — for everyday purposes they are equivalent, but UTC is the precise scientific standard. Z (Zulu) is the military and ISO 8601 shorthand for UTC+0. All three represent the same offset; prefer UTC or Z in API responses.
Are there timezones with a fixed offset that never change for DST?
Yes. Timezones like UTC, Asia/Tokyo (JST, always UTC+9), and Asia/Kolkata (IST, always UTC+5:30) never observe DST. If you need a guaranteed fixed offset, use "Etc/GMT+5" style identifiers — though note these use the POSIX sign convention, so "Etc/GMT+5" is actually UTC−5.
How do I specify a timezone in API requests?
Most REST APIs accept IANA timezone identifiers as strings — for example, the Google Calendar API uses "timeZone": "America/Los_Angeles". If an API requires a UTC offset instead, use ISO 8601 format: 2026-05-09T18:00:00-07:00. Avoid passing abbreviations (EST, PST) as they are not standardized across APIs.

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