How the Online Meeting Time Zone calculator works

Scheduling across time zones is deceptively hard because “10:00 AM” is not a single universal moment. The same clock time represents different instants depending on location, and those relationships can change throughout the year due to Daylight Saving Time (DST). This calculator solves the problem in three steps: (1) interpret your selected meeting date/time in the organizer’s time zone, (2) convert that instant into each participant’s local time zone, and (3) (optionally) check whether the result sits inside each person’s preferred workday window.

The key idea is that there is only one “true” meeting instant: the moment in UTC (Coordinated Universal Time). Time zones are just different ways of displaying that same instant on a local clock. So instead of trying to directly convert “Chicago 10:00 AM → London ???” we convert the organizer’s time into UTC first, then format UTC into each participant’s local time. This avoids most DST bugs and makes date changes (like crossing midnight) automatic.

When you choose a meeting date and time, you’re choosing a local clock reading inside the organizer’s time zone. Internally, we convert that local clock reading into a UTC timestamp. Conceptually:

UTC time = Local time − Time zone offset

The tricky part is the “time zone offset” because it depends on the date (DST) and the selected time zone. This tool uses your browser’s built-in Intl.DateTimeFormat time zone data to compute the correct offset for that date and place. It works without any external API calls.

Once we have the UTC instant, getting local times is straightforward: we format that same instant using each participant’s time zone. If the meeting crosses midnight for a participant, the calculator shows the date change clearly (for example, “Tue → Wed”).

If you enable overlap mode, the calculator creates a local “work window” in each time zone (for example, 09:00–17:00) for the selected date. Then it converts each work window into UTC and computes their intersection. If the intersection is empty, there is no single time that lands inside everyone’s work hours for that date. If the intersection exists, you’ll see the overlap window in UTC terms and the suggested “best time” as the midpoint of that overlap.

Imagine you schedule a meeting for March 12 at 10:00 in America/Chicago with a 45-minute duration, and your teammates are in America/Los_Angeles, Europe/London, and Asia/Kolkata. The calculator converts the organizer time into a UTC instant, then displays each participant’s local time. You’ll immediately see that India may be late evening, and London may be afternoon — plus whether any of those times fall outside the chosen work hours.

DST is the reason a meeting that used to be “Chicago 10:00 AM = London 4:00 PM” can become “Chicago 10:00 AM = London 3:00 PM” on different dates. In other words, the offset changes. By computing the offset using the actual date and the selected time zone, the calculator stays accurate during DST periods and around transition weeks.

Bottom line: if you treat time zones as a “two-step conversion through UTC,” you get reliable scheduling, and your meeting invitations stop drifting mysteriously across seasons.

Frequently Asked Questions

• Does this handle Daylight Saving Time automatically?

  Yes. The conversion uses your browser’s time zone database (IANA time zones via Intl) and applies the correct offset for the selected date, including DST.

• What if someone’s time crosses midnight?

  The table shows the local date alongside the local time, so it’s obvious if the meeting is on a different day for a participant.

• What does “Overlap window” mean?

  It means a range of times where the meeting would fall inside each person’s local work hours (like 09:00–17:00). If there is no overlap, the calculator tells you.

• Is this accurate for every country and city?

  It’s as accurate as the time zone data built into the browser. For most modern browsers, that’s very reliable. Still, for high-stakes meetings (medical, legal, financial deadlines), confirm with a calendar invite.

• Can I share this in Slack or WhatsApp?

  Yes. Use the share buttons or the Copy button to paste a clean meeting card into any chat.

• Do you store my meeting data?

  No. Conversions happen locally in your browser. If you click “Save Setup,” it stores only on your device in local storage.