Date & Time
Timezone Overlap Calculator
Find the working-hour overlap between two timezones - useful for cross-office meetings.
Zones
Working hours
Same range applied to both zones. Default 9-17.
Overlap
8 hours overlap: UTC 09:00–17:00 ↔ UTC 09:00–17:00
About this tool
Pick two IANA timezones and a working-hour range (default 09:00-17:00, same range applied to both zones) and see how many hours of overlap the two offices have today, expressed as a wall-clock window in each zone. Uses the browser's Intl.DateTimeFormat so daylight-saving transitions are handled automatically for whichever date is 'today' in each zone.
FAQs
Why is there no date input?
The tool always uses 'today' - each zone's current calendar date. If you need to plan a meeting weeks out across a DST boundary, cross-check with the timezone-converter tool.
Can I set different working hours per zone?
Not yet - the range you type is applied to both zones (so 9-17 means both offices work 9-17 local). Asymmetric schedules are a common ask; open an issue if that's what you need.
Does it handle overnight shifts (e.g. 22-06)?
No. End must be after start on the same day. Overnight wrap-around is intentionally left out.
Why do half-hour zones like IST show a fractional overlap?
India is UTC+5:30, Nepal is +5:45. When one side of a comparison has a half-hour offset the overlap can end mid-hour. The result shows the exact wall-clock endpoints in each zone.
Is anything sent to a server?
No. Everything runs in your browser via Intl.DateTimeFormat - the same timezone database your OS ships.