Direct answer
Business-hours overlap is the intersection of each region's 09:00–17:00 window after converting to a common reference. Overlap shrinks one hour for every hour of offset difference up to 8 hours; beyond that, it is zero.
The overlap formula
Overlap (hours) = 8 − |offset difference|, clamped at 0. Two cities 5 hours apart share 3 hours of overlap inside a standard 09:00–17:00 day.
If you extend the 'fair' day to 08:00–18:00 (10 hours), overlap = 10 − |Δ|. Most professional teams use 8 because it matches a real working day after lunch and focus blocks are subtracted.
City-pair comparison table
Use this lookup before you propose a meeting time.
- New York ↔ London: Δ = 5h, overlap ≈ 3h (13:00–18:00 London).
- London ↔ Berlin: Δ = 1h, overlap ≈ 7h.
- London ↔ Dubai: Δ = 4h, overlap ≈ 4h.
- London ↔ Singapore: Δ = 7h, overlap ≈ 1h.
- New York ↔ San Francisco: Δ = 3h, overlap ≈ 5h.
- New York ↔ Sydney: Δ = 14/15h, overlap ≈ 0h.
Scheduling examples
Translate the overlap window into a concrete invite.
- 3-hour overlap → one 60-minute meeting + 2 hours of buffer for prep/wrap.
- 1-hour overlap → 25-minute focused sync; no agenda overflow.
- 0-hour overlap → async only; rotate live meetings monthly.
Integrate overlap into your workflow
Treat overlap as a budget your team spends each week. Run the meetings that need bandwidth there; push everything else to async.
- Block the overlap window in shared calendars as 'cross-region time'.
- Reserve it for decisions, design reviews, and unblocking.
- Move status, FYIs, and 1:1s outside the window.
- Audit monthly: are you spending overlap on the highest-value work?
Frequently asked questions
How do I calculate business-hours overlap between two cities?
Subtract their UTC offsets, take the absolute value, then compute 8 minus that number. Anything ≤ 0 means no shared business hours.
What counts as 'fair' business hours for overlap?
Most teams use 09:00–17:00 local. Some extend to 08:00–18:00 for a slightly larger pool at the cost of pre-coffee or after-dinner meetings.
Does DST change my overlap window?
Yes — twice a year. When one side shifts and the other does not, overlap can grow or shrink by an hour for a few weeks.