Time zone vs UTC offset
Offsets tell you the current difference from UTC; time zones include rules (like DST) that can change by date.
A UTC offset is a simple number like UTC+05:30. It’s correct only for a specific instant.
A time zone like America/New_York or Europe/London contains historical rules, including daylight saving transitions, so the offset can change depending on the date.
- Europe/London can be UTC+00:00 in winter and UTC+01:00 in summer (BST).
- Asia/Kolkata stays UTC+05:30 year-round (no DST).
Try it: Convert between zones
Prefer IANA time zones over fixed offsets for real-world scheduling.
How conversion works (instant-first)
Correct conversion is always: local time + source zone → instant → target zone local time.
When you enter a local time and a source time zone, the converter finds the exact instant it represents. Then it projects that instant into the target time zone.
This approach is why the target date can change (previous/next day). You are converting an exact moment, not just adding/subtracting hours.
- Asia/Kolkata 09:00 is UTC 03:30 (same date).
- Converting that instant to America/Los_Angeles may land on the previous day.
Try it: See date shift
Convert by instant, not by “time difference math”.
DST gotchas: ambiguous & non-existent times
DST creates two special cases: a repeated hour (ambiguous) and a skipped hour (non-existent).
On “spring forward”, some local times are skipped. For example, 02:30 may not exist in a zone on that day.
On “fall back”, an hour can repeat, so the same local time can map to two different instants. You must pick which occurrence you mean.
- Spring forward: 2026-03-08 02:30 is non-existent.
- Fall back: 2026-11-01 01:30 is ambiguous (occurs twice).
Try it: DST edge cases
If a time is ambiguous, always specify the occurrence or share the time in UTC.
Using the calculator (multi-zone + slider)
Compare up to five zones at once and experiment with a live time slider.
Use “Sync now” to jump to the current system time instantly — useful for quick checks.
Add more target zones to compare times side by side. The results table highlights previous/next-day shifts.
The Time Explorer slider lets you scrub through the day and see when overlapping working hours occur.
- Set From: Asia/Kolkata, add London, New York, and Tokyo.
- Drag the slider to find a time that avoids late-night hours for most zones.
Try it: Multi-zone comparison
Multi-zone view + slider = faster scheduling decisions.
Best practices for meetings & travel
Avoid confusion by sharing a reference zone, and double-check DST around travel dates.
For international meetings, share the time in one reference zone (often UTC) plus the target zone conversion.
If you’re traveling, set “from” as the local zone where the event occurs, not where you are today.
When scheduling around DST weeks, prefer mid-day times and avoid the transition hour.
- Use IANA zones (America/New_York), not just GMT offsets.
- Check if the target date is near a DST change.
- Share UTC time for critical events.
Try it: Travel planning
For high-stakes scheduling, always include the zone name and UTC time.