Elapsed time, overnight times, and adding durations
The elapsed-time mode subtracts the start clock time from the end clock time. When the end time is earlier than the start time, it assumes the interval crosses midnight. For example, 11:30 PM to 1:15 AM is 1 hour 45 minutes under that assumption.
Adding or subtracting a duration
The second mode adds or subtracts the hours and minutes you enter from a starting clock time. For example, 9:20 AM plus 2 hours 45 minutes is 12:05 PM. Times wrap around the 24-hour clock, and the result indicates if the calculation falls on a different day.
Important limitations
- For elapsed time, an end time before the start is interpreted as the next day; this input form cannot tell whether you actually intended a different date.
- The calculator works with clock times and durations, not full date-time stamps. It does not account for time zones, daylight-saving changes, or the exact duration between timestamps on different dates.
- For work shifts or travel, check whether breaks or intermediate days must be included before using the total.
Tips for accurate results
Time is base 60, so carry over at 60 minutes rather than 100. For example, 2 hours 45 minutes plus 1 hour 30 minutes is 4 hours 15 minutes. This is useful for adding up shifts, travel legs, or workout durations.
Common mistakes and limits
Decimal hours are a common trap: 1.5 hours is 1 hour 30 minutes, and 1.75 hours is 1 hour 45 minutes, not 1 hour 75 minutes. When working with clock times across midnight or between time zones, double-check the day and the offset.