WhenMathTime Interval Overlap Calculator
Find the window of time that every interval you enter has in common, such as everyone's shared availability. Enter 2 to 8 intervals; the result is the time all of them overlap, or a clear statement that none exists.
Worked example
Three colleagues are free 09:00-13:00, 10:00-12:00, and 11:00-15:00. The overlap is the latest start (11:00) to the earliest end (12:00): 11:00-12:00, one hour common to all three. If any two intervals only touch, like 09:00-10:00 and 10:00-11:00, that shared endpoint is not counted as overlap, since intervals are treated as including their start but not their end.
Common mistakes
- Expecting adjacent (touching) intervals to count as overlapping; they do not.
- Forgetting an interval crosses midnight, which needs its own next-day confirmation.
Limitations
This finds a common clock window only; it does not know participants' time zones. For that, see Time Zones & Meetings.
Frequently asked questions
- What if there's no common time at all?
- The result states plainly that no time is common to all intervals, rather than showing a confusing zero-length range.