Time Zone Meeting Planner

How this is calculated

THE OVERLAP IS COMPUTED IN YOUR OWN CLOCK, which is the frame you have to book in anyway. Their working day is shifted by the difference between the two UTC offsets, and the overlap is whatever the two windows share. ⚠️ THE OVERLAP CAN LIVE ON THEIR NEXT DAY, AND THIS IS THE PART MOST MENTAL ARITHMETIC MISSES. If you work 09:00-17:00 in UTC-8 and they work 00:00-08:00 in UTC+1, there is no overlap at all on the same calendar day - but their following morning lands squarely inside your afternoon, giving two real hours. The tool tests their working day on the previous, same and next day and reports the best of the three. Checking only the same day reports zero for a window that exists. ENTER UTC OFFSETS, NOT ZONE NAMES. A zone name does not fix an offset - most of Europe and North America shift by an hour for part of the year, and the two continents do not shift on the same dates, so for a couple of weeks each spring and autumn the usual difference is an hour out. Look up the offset that applies on the DATE of the meeting rather than the one that applies today. HALF-HOUR AND QUARTER-HOUR OFFSETS ARE REAL. India is UTC+5:30, Nepal is UTC+5:45, parts of Australia are UTC+9:30, and Chatham Island is UTC+12:45. Enter 5.5 for India, 5.75 for Nepal. A planner that only accepts whole hours quietly excludes about a fifth of the world. THE LATEST START IS THE FIGURE TO ACTUALLY BOOK FROM. A three-hour overlap does not mean you can start a one-hour meeting at any point in it - starting at the end leaves nothing. The latest start is the end of the overlap minus your meeting length. If your meeting is LONGER than the whole window it cannot fit at all, and the tool shows a dash there rather than a time you could not actually use. A DASH MEANS THERE IS NO OVERLAP AT ALL on any of the three days tested. That is a real answer and a common one: two standard nine-to-five days about twelve hours apart genuinely share no working time. The honest options then are that somebody works outside their normal day, or that the conversation happens asynchronously. CLOCK TIMES ARE SHOWN AS HOURS AND MINUTES, so "16h 30m" means 16:30, not a duration of sixteen and a half hours. Midnight is the one awkward case and shows as "0m".

Common questions

Why does it ask for UTC offsets instead of city names?

Because a city name does not fix an offset. Most of Europe and North America shift by an hour for part of the year, and crucially they do not shift on the same dates - so for a couple of weeks each spring and autumn the usual difference between London and New York is an hour off what everyone assumes. A planner built on zone names has to carry a rules database that goes stale, and governments change these rules with very little notice. Asking for the offset that applies on the date of the meeting puts the one judgement call in front of you rather than hiding it.

What if there is no overlap?

Then the tool shows a dash, and that is a real answer rather than a failure. Two standard nine-to-five days about twelve hours apart genuinely share no working time - no amount of arithmetic will find some. The honest options at that point are that one person works outside their normal day, that you alternate who takes the inconvenient slot, or that the conversation happens in writing instead. A planner that produced a plausible-looking time anyway would be worse than one that says there isn't one.

Why does it check their next day?

Because that is where a lot of real overlap lives, and it is the part mental arithmetic misses. Take someone working 09:00 to 17:00 in UTC-8 and someone working 00:00 to 08:00 in UTC+1. On the same calendar day the two windows share nothing. But the second person's FOLLOWING morning lands squarely inside the first person's afternoon, and there are two genuine hours available. The tool tests their working day on the previous, same and next day and reports the best of the three, so an overlap that exists is never reported as zero.

What is the latest start for?

Booking. A three-hour overlap does not mean a one-hour meeting can begin anywhere inside it - start at the end and there is no time left. The latest start is the end of the overlap minus your meeting length, and it is the figure to actually put in a calendar invite. If it comes out earlier than the start of the overlap, the meeting is longer than the window and does not fit at all.

Does it handle half-hour time zones?

Yes, and it needs to. India is UTC+5:30, Nepal is UTC+5:45, parts of Australia are UTC+9:30 and Chatham Island is UTC+12:45. Enter 5.5 for India and 5.75 for Nepal. Roughly a fifth of the world's population lives somewhere with a fractional offset, so a planner that only accepts whole hours is quietly excluding them - the inputs here step in quarter hours for that reason.

Should I book in my time zone or theirs?

Neither, ideally - book in a calendar application that stores the underlying instant and renders it in each person's local time. That way nobody converts anything and a daylight-saving change cannot silently move the meeting for one side only. If you have to write a time in an email, write both and name the zones explicitly, and prefer the UTC offset over an abbreviation: 'CST' means US Central, China Standard and Cuba Standard depending on who is reading.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Time Zone Meeting Planner at https://www.bfcbrilliance.com/tools/time-zone-meeting-planner.

What I entered:
- Your UTC offset (h): ___
- Their UTC offset (h): ___
- Your working day starts (24h): ___
- Your working day ends (24h): ___
- Their working day starts (24h): ___
- Their working day ends (24h): ___
- Meeting length (h): ___

What it calculated:
- Hours you can both make: ___
- They are ahead of you by: ___
- Overlap starts - your clock: ___
- Overlap starts - their clock: ___
- Latest you can start - your clock: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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