How to coordinate meetings across timezones without losing your mind

Someone joined a call I was on last year an hour late. Not because they forgot — because the invite said "10am" and they assumed that meant Pacific, when it was actually Eastern. One hour's difference, one missed assumption, one very awkward start to what should have been a straightforward meeting.

It happens more than it should. And it's almost always avoidable.

The assumption nobody notices they're making

"10am Tuesday" feels like a complete piece of information. It isn't. Without a timezone attached, it's an instruction that each person on the invite will quietly interpret using their own local context.

The New York-based attendee reads it as Eastern. The California-based one adds three hours — unless they've spotted that the organiser is East Coast, in which case they might second-guess themselves. The person in London converts from GMT and hopes there's no daylight saving complication. The result is that "10am" becomes a different time for everyone, silently, without anyone raising it until someone shows up at the wrong hour.

The "Wait, I thought this was at 10am?" moment is one of the most common things that goes wrong in cross-timezone scheduling. The fix is simple: always include the timezone, and ideally include the local equivalent for each person on the call. "10am ET / 3pm GMT / 4pm CET." It takes ten seconds and removes the silent translation step entirely.

When the maths gets genuinely hard

Even with explicit timezones, the coordination itself is difficult once you're dealing with a wide enough spread.

Take five people across California, New York, London, Germany, and Beijing. California to New York is three hours. New York to London is five. London to Germany is one. California to Beijing is fifteen. The window where it's a reasonable working hour for all five simultaneously is small. Sometimes it doesn't exist.

In practice, that means someone ends up on a call at an inconvenient time. Working out who and when requires converting every proposed slot into every relevant timezone, cross-referencing against what each person has already said they can or can't do, and repeating the process every time something changes. It's not complicated work, but it takes time — and it resets from scratch with every new group.

Most people underestimate how long this actually takes. It's not five minutes. Spread across a week of emails, it's often hours.

A few things that help

Always state times with a timezone and the local equivalent for each person. Never assume "morning" means the same thing to everyone.

Check clock changes carefully — the US, UK, and EU don't switch on the same dates, which means offsets you relied on last month may have shifted.

And acknowledge it when someone is joining at an awkward hour to accommodate others. It's a small thing that costs nothing.

Beyond the practical habits, the bigger shift is moving away from tools that ask people for their availability and toward tools that can read it directly. If the system already knows when everyone is free — and accounts for their timezone automatically — the coordination maths disappears. You stop calculating and start confirming.

Here's how Whenn does this

None of the manual steps above are necessary once the tool can read everyone's calendar directly.

When a participant connects their Google or Microsoft calendar, Whenn already knows their timezone — it's part of their calendar settings. There's no asking, no converting, no cross-referencing by hand. AutoWhenn reads every participant's availability in their own local time, works out the overlap automatically, and proposes a slot that's already been checked against everyone's timezone.

The example below shows what that looks like in practice — the same five-timezone scenario from earlier in this piece, confirmed automatically, with each participant's local time shown correctly without anyone doing the maths.

Whenn handles the entire coordination process — automatically.

Add participants by email, they connect their calendar, AutoWhenn finds the best slot and sends everyone an invite.