Time-Zone Overlap Calculator
Add 2–6 regions and see the hours they all share inside reasonable working time — perfect for scheduling collabs, sponsor calls and cross-continent streams.
How it works
For every UTC hour of the day (0–23), the calculator asks your browser's Intl API "what's the local hour in each region at this moment?" — that's the row of numbers you see in the grid. A cell is highlighted green when it falls inside that region's working hours. A column is highlighted violet when every region has a green cell there — that's a shared overlap hour. Consecutive overlap hours are grouped into the "best window" summary at the bottom.
How to use this tool
- Add the regions you need to coordinate — pick from the dropdown and hit Add.
- Adjust the working-hours range if 9–18 doesn't match your rhythm (evening streamer? night owl podcast? nudge the end hour later).
- Read the grid: green cells are OK, violet columns are shared overlap.
- Scroll to the summary below the grid to see the best overlap window written out in each region's local time — that's your candidate list.
- Copy the summary and share it with your collab partner or team.
Frequently asked questions
What if there's no overlap at all?
The summary will tell you no shared hour exists inside the current working window. Widen your working hours (e.g. 7:00–20:00) — often you'll find an evening/morning slot that works for both sides. If regions are truly opposite (Auckland vs Los Angeles), an async format may be more realistic than a live call.
Does the tool handle daylight saving time?
Yes — it uses today's date to compute each region's UTC offset via the IANA database. That means the overlap is correct for right now. If you're planning several months ahead across a DST transition, spot-check the days close to the shift.
Why 9:00–18:00 by default?
It's a widely-accepted definition of "reasonable working hours" that isn't tied to a specific job culture. You can shrink or expand it — the calculation reacts instantly to whatever range you set.
Why is the maximum 6 regions?
Beyond about 4–6 regions the odds of a shared working hour drop to zero, and the grid becomes hard to read. Six covers almost every realistic collab scenario. If you need more, split the group into two calls with an overlap between them.
Can I share this schedule with someone?
Yes — hit Copy Result to grab the summary as plain text (regions + best overlap window in each region's local time). Paste into Discord, Slack, email or your calendar invite.