Time Zone Converter

Free time zone converter. Convert a date and time between any two IANA time zones (e.g. New York to London, Tokyo to UTC) with daylight saving time handled automatically.

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This tool has a free JSON API. Copy a prompt or skill below to use it with ChatGPT, Claude, or any AI agent — no API key needed.

API docs
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Enter a date and two time zones.

How time zone converter works

A time zone converter takes a wall-clock date and time in one time zone and shows the same instant in another zone. The trick is that local time on a clock is not an absolute moment — you must account for each zone offset from UTC, including daylight saving time, before the conversion is correct.

This converter uses IANA time zone names (like America/New_York or Asia/Kolkata) and the JavaScript Intl API, which knows the historical and current offset and daylight saving rules for each zone. Enter the source date and time and pick the two zones; the tool resolves the source instant and formats it in the target zone, showing both offsets (for example GMT-04:00 and GMT+01:00).

Always use the full IANA name rather than an abbreviation. "EST" is ambiguous (it can mean US Eastern or Australian Eastern), while "America/New_York" is unambiguous and auto-switches between standard and daylight time. When scheduling across zones, double-check the offsets shown — DST changes mean the same conversion can differ by an hour depending on the date.

Frequently asked questions

What format should the date and time be in?
Use the date and time picker (YYYY-MM-DD and HH:mm). The time is interpreted as wall-clock time in the "from" zone you select, not as UTC or your local time.
Why use IANA time zone names?
IANA names like America/New_York or Europe/London are unambiguous and encode daylight saving rules, so the converter handles DST automatically. Abbreviations like EST or IST are ambiguous and differ by region.
Does it account for daylight saving time?
Yes. The converter uses the JavaScript Intl database of time zone rules, so it applies the correct offset for the specific date, including historical and future DST changes. The same zones can convert differently in summer and winter.
How accurate is the conversion?
Conversions use the full IANA time zone database built into the runtime and are correct for any past or future date. The one edge case is ambiguous local times during a DST fall-back transition (a clock hour that repeats), which the tool resolves by the standard-time offset.

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