How to use this developer tool
- Enter a local date and time.
- Select the source IANA timezone.
- Enter one or more target zones.
- Review converted dates, offsets, and day changes.
#079 · Time & Date Tools Developer Tool
Timezone Converter
Convert a local date and time between IANA timezones, compare multiple destinations, and show UTC offsets, day changes, and daylight-saving behavior.
Developer Input
Time & Date ToolsAd space
What this developer tool does
The converter resolves a wall-clock time in the source timezone to an instant, then formats that instant in each target timezone.
Parse local components → solve source timezone offset iteratively → normalize to UTC → format each target with Intl.DateTimeFormat.
DST transitions can create ambiguous or nonexistent local times. Results should be reviewed around transition boundaries.
Example
Convert 2026-07-11 18:00 in Asia/Seoul to New York, London, and Tokyo.
Tips for better output
- Use IANA names rather than fixed abbreviations.
- Check whether the target date moves to the previous or next day.
- Review DST-sensitive meeting times near seasonal transitions.
FAQ
How do I convert Seoul time to New York time?
Resolve the Seoul local time to UTC, then format the same instant in America/New_York.
Why does the converted timezone show the previous day?
The target offset may move the instant across a calendar-day boundary.
How do I account for daylight saving time in timezone conversion?
Use an IANA timezone so Intl applies the historical offset for the selected date.
What is the difference between a timezone and a UTC offset?
A timezone includes historical and daylight-saving rules, while an offset is only a fixed displacement.
How do I compare one meeting time across multiple timezones?
Provide several comma-separated target IANA zones and review the generated table.
Related developer tools
Timezone output
| Column | Meaning |
|---|---|
| Local time | Formatted target time |
| Offset | UTC displacement |
| Day change | Previous, same, or next date |