Time Zone Overlap Planner
Work out the shared window once, write it down in both clocks, and stop recomputing it every time somebody suggests a slot.
BFCBrilliance · bfcbrilliance.com/tools/time-zone-meeting-planner
The pair
- Date of the meeting
- Your city
- Your UTC offset on that date
- Their city
- Their UTC offset on that date
- DIFFERENCE
- Your working day
- Their working day
- OVERLAP (your clock)
- OVERLAP (their clock)
- Latest start for a 1 h meeting
Other people on the call
| Name | UTC offset | Working day | Their clock at your overlap start |
|---|---|---|---|
The arithmetic
- Difference
- their UTC offset − yours
- Their day in your clock
- their hours − the difference
- Overlap
- the part both windows share
- ⚠ Also check
- their PREVIOUS and NEXT day
- Latest start
- overlap end − meeting length
- Meeting longer than window
- a dash — it does not fit at all
- No overlap
- a real answer, not an error
Fractional offsets that catch people out
- India
- UTC+5:30 — enter 5.5
- Nepal
- UTC+5:45 — enter 5.75
- Iran
- UTC+3:30 — enter 3.5
- Adelaide / Darwin
- UTC+9:30 — enter 9.5
- Newfoundland
- UTC−3:30 — enter −3.5
- Chatham Island
- UTC+12:45 — enter 12.75
Before you send the invite
- Offsets looked up for the DATE of the meeting, not for today
- Checked whether either side changes clocks between now and then
- Both continents' daylight-saving dates checked — they differ
- Meeting length fits before the latest start
- Written in both clocks, with zones named
- Sent from a calendar that stores the instant, not the text
- Avoided bare abbreviations — 'CST' means three different zones
- Agreed who takes the inconvenient slot next time
The overlap may be on their tomorrow
Someone working 09:00-17:00 in UTC-8 and someone working 00:00-08:00 in UTC+1 share nothing on the same calendar day. Their next morning, however, sits inside your afternoon and gives two real hours. Always check the adjacent days before concluding there is no window.
'CST' is three different time zones
US Central, China Standard and Cuba Standard all abbreviate to CST, and there are worse examples. Abbreviations are ambiguous and not standardised anywhere. Write the UTC offset, or better, send a calendar invitation that stores the actual instant and lets each person's software render it locally.