What is the IANA timezone database?

The IANA Time Zone Database (also called tz database or zoneinfo) is the authoritative source for timezone rules used by Linux, macOS, iOS, Android, and most programming languages. It defines timezone identifiers in the form "Region/City" (e.g. "Europe/Paris") and tracks the entire history of UTC offsets and daylight saving time rules for every timezone worldwide.

What is the difference between UTC offset and a timezone?

A UTC offset (like +05:30 or -08:00) is just a fixed number of hours and minutes from UTC. A timezone (like "Asia/Kolkata" or "America/Los_Angeles") is a named region that may have different UTC offsets at different times of year due to daylight saving time. For programming, always store and process times using IANA timezone names, not raw offsets, to handle DST changes correctly.

Why should I use timezone identifiers instead of abbreviations like EST or PST?

Timezone abbreviations are ambiguous — EST can mean Eastern Standard Time (UTC-5), Australian Eastern Standard Time (UTC+10), or other zones. IANA identifiers like "America/New_York" or "Australia/Sydney" are globally unambiguous, handle DST automatically, and are the correct input for all modern date/time libraries (Luxon, date-fns, Temporal API).

Timezone Reference | CodeLint.Dev

Practical rules

Store past events as UTC instants —What happened is fixed. No later rule change should alter a log entry or an audit record.
Store future events as local time plus zone —A 9am meeting should stay at 9am if a government changes the DST rules. Stored as a UTC instant, it silently moves.
Keep tzdata updated —The database is revised several times a year, sometimes with only weeks of notice before a change takes effect. A container image pinned long ago has stale rules and fails silently.
Etc/GMT signs are inverted —Etc/GMT+5 is UTC−5, not UTC+5. This follows the POSIX convention and catches everyone exactly once.
Do not use three-letter zones in code —EST5EDT and similar legacy identifiers exist for compatibility but lack proper historical data.
Zone names are not user-facing —Asia/Kolkata is correct and Asia/Calcutta is a deprecated alias that still resolves. Display a friendly label, store the canonical identifier.

About

The Timezone Reference lists all IANA timezone identifiers (such as "America/New_York" or "Asia/Kolkata") with their current UTC offset and live local time. It is invaluable when configuring servers, scheduling jobs, or building applications that need to handle users across multiple time zones correctly.

How to use

1 Browse all IANA time zones or filter by region using the dropdown.
2 The current UTC offset and live local time update automatically.
3 Search for a specific city or zone identifier.
4 Click any row to copy the IANA timezone string.

What is the IANA timezone database?: The IANA Time Zone Database (also called tz database or zoneinfo) is the authoritative source for timezone rules used by Linux, macOS, iOS, Android, and most programming languages. It defines timezone identifiers in the form "Region/City" (e.g. "Europe/Paris") and tracks the entire history of UTC offsets and daylight saving time rules for every timezone worldwide.
What is the difference between UTC offset and a timezone?: A UTC offset (like +05:30 or -08:00) is just a fixed number of hours and minutes from UTC. A timezone (like "Asia/Kolkata" or "America/Los_Angeles") is a named region that may have different UTC offsets at different times of year due to daylight saving time. For programming, always store and process times using IANA timezone names, not raw offsets, to handle DST changes correctly.
Why should I use timezone identifiers instead of abbreviations like EST or PST?: Timezone abbreviations are ambiguous — EST can mean Eastern Standard Time (UTC-5), Australian Eastern Standard Time (UTC+10), or other zones. IANA identifiers like "America/New_York" or "Australia/Sydney" are globally unambiguous, handle DST automatically, and are the correct input for all modern date/time libraries (Luxon, date-fns, Temporal API).

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