Processed locally in your browser — not uploaded
Timezone Converter & World Clock
Convert a date and time from one city to any number of others at once, with automatic daylight-saving-time handling — the UTC instant is resolved from your base city's wall-clock time, then re-rendered in every selected zone. Each city shows its converted time, date (with a +1/-1 badge when the day differs from the base), UTC offset, and whether it falls within typical 9am-6pm business hours. Runs entirely in your browser using the built-in Intl time zone database.
12:14 AM
01:14 AM
04:14 AM
09:14 AM
10:14 AM
How to use
- Pick a base city and a date/time, or click "Now" to use the current moment.
- Add any number of cities to compare — each shows its converted local time, date, UTC offset, and whether it falls within typical business hours (9am-6pm local).
- A +1/-1 badge appears when a city's local date differs from the base city's date, so you don't miscount an overnight meeting.
- Conversion is DST-aware: it resolves the actual UTC instant for the wall-clock time you entered in the base city's zone, then re-renders that instant in every other selected zone.
Understanding the output
Each city's time is computed via the browser's built-in Intl.DateTimeFormat with that city's IANA time zone — no timezone database or library is bundled, and nothing is sent to a server. Offsets (e.g. GMT+4) reflect the actual offset in effect on the selected date, correctly accounting for daylight saving time in zones that observe it.
Common issues & tips
- •Time looks off by exactly one hour: check whether the date you picked falls near a DST transition — some zones shift clocks on different dates than others, so two "UTC-5" cities in winter may diverge in summer.
- •During the one hour a DST transition creates an ambiguous or skipped local time (e.g. the repeated or missing hour at 2am), conversion resolves to one of the two possible instants rather than asking you to disambiguate.
- •Business-hours highlighting is a fixed 9am-6pm local-time heuristic, not each city's actual working-week or public holiday calendar.
Frequently asked questions
- Does this tool account for daylight saving time?
- Yes. Conversion resolves the actual UTC instant for the wall-clock time you enter in the base city's time zone, then formats that instant in each target zone — so offsets automatically shift on each zone's real DST transition dates, not a fixed number.
- Is my selected time or city sent anywhere?
- No. All conversion runs in your browser via the Intl.DateTimeFormat API built into JavaScript — no data leaves your device.