How to Send Availability Across Time Zones

The failure mode

Someone sends "how about Tuesday at 10?" to a person three zones away. The reply says yes. One of them joins at the wrong hour, and neither finds out until the call is already awkward.

It is not a maths problem. It is a formatting problem. The fix is to make the time unambiguous in the body of the email, before anyone has to convert anything.

Rules that prevent the mistake

1. Never send a bare time. Every time you write gets a zone label. "10:00 AM" is a guess. "10:00 AM ET" is a fact.

2. Use the recipient's zone as the primary. You know your own schedule. They have to act on the email. Put their zone first and yours in parentheses if you need it there at all.

3. Use abbreviations people recognise, and spell out the offset when the audience is international. ET, CT, MT, PT work fine inside the US. For anyone outside it, write "9:00 AM New York (UTC-4)" or name the city. City names beat abbreviations: half the world reads "CST" as China Standard Time.

4. Include the date and the weekday. "Tue Sep 22" catches an off-by-one that "9/22" does not, and date order differs by country.

5. Watch daylight saving. The US, the EU and Australia change on different dates, and much of the world never changes at all. For anything more than two weeks out, the offset between two cities may not be the offset today. State the wall-clock time in each city rather than the difference between them.

6. Give windows, not pinpoints. "2:00-4:00 PM London" is easier to accept than a single instant, and it absorbs small conversion errors.

A format that works

Times below are Pacific, with London in brackets:

• Tue Sep 22, 8:00-9:30 AM PT (4:00-5:30 PM London)
• Wed Sep 23, 9:00-10:00 AM PT (5:00-6:00 PM London)
• Thu Sep 24, 7:30-9:00 AM PT (3:30-5:00 PM London)

Reply with one and I will send the invite with a Teams link.

Three options. Both zones. Weekday and date. One instruction. The recipient can answer from a phone in the elevator.

Finding the overlap first

Before you write anything, decide what the shared working window even is. Two examples:

• New York and London: five hours apart. The honest overlap is roughly 9:00 AM to noon Eastern, which is 2:00 to 5:00 PM in London. Offer times inside it.
• San Francisco and Berlin: nine hours. There is no comfortable overlap. Somebody takes an early morning or a late evening. Say so in the email and offer the choice rather than pretending the 7:00 AM slot is normal.

If your only overlap is outside working hours, name it. "Our working days barely overlap, so both options are early for me and late for you — pick whichever is less bad" reads as respect. Silently offering someone a 9:00 PM call does not.

Do not make the recipient click to find out

Booking links solve the conversion problem by showing times in the visitor's browser zone, and for cold inbound that is a fine trade. But a link asks for a click, a page load and often a sign-in before anyone knows whether the times are workable. For a warm thread, an internal exec, a candidate or a client who is already mid-conversation, times in the body of the email are faster and harder to ignore.

The cost of the manual route is the calendar arithmetic: read your free/busy, subtract what you will not offer, then convert everything into a zone you do not live in.

Generating the list in the right zone

OpenSlot builds the list for you and outputs it in any time zone, so the conversion is done before the text reaches your email.

• Reads Microsoft 365 free/busy read-only through delegated Microsoft Graph scopes. It uses only the availability and stores no calendar data. Availability is computed live each time you ask.
• "Just me" for your own availability, or "Me + others" to merge colleagues into one combined list.
• Any time zone, a window of up to 60 days on Pro (seven on the free plan), working hours that default to 8-5 and hold in your time zone and theirs, a minimum slot length, weekends on or off, and an option to count tentative as busy.
• Settings roam across devices, so the zone and working hours you set on your laptop are there on the web app.
• Web app plus an Outlook add-in for Windows, Mac and Outlook on the web. The add-in inserts the list straight into the email you are writing.

Free covers you plus one person with a 7-day window. Every new account starts with a 14-day Pro trial, no card. Pro is $7 per user per month or $72 a year. Team starts at $5 per user per month, minimum five seats, with volume tiers. Billing is self-serve through Stripe. The add-in is listed on Microsoft Marketplace; OpenSlot LLC is a Microsoft verified publisher.

If your correspondents are mostly strangers who arrive from a website, a booking page with automatic zone detection is probably the better fit. If they are people you are already emailing, send the times.

Related

• How to write an availability email
• Send team availability to an external client

Questions: support@useopenslot.com or the help pages.