Time Duration Calculator

Worked example

A shift runs from 09:15 to 17:45 the same day. The duration is 8 hours 30 minutes: convert both times to seconds since midnight (9×3600 + 15×60 = 33,300 and 17×3600 + 45×60 = 63,900), subtract (63,900 - 33,300 = 30,600 seconds), and convert back (30,600 / 3600 = 8.5 hours, or 8h 30m). If the end time is numerically earlier than the start, such as 22:00 to 06:00, the calculator asks you to confirm the end falls on the next day rather than guessing; once confirmed, the same subtraction runs against a 24-hour-extended end time, giving 8 hours.

Clock time versus elapsed time

Clock mode answers "how much time is on the clock between these two times," and never needs a date or time zone. Date and time zone mode answers a different question: "how much real time actually passed," which matters whenever a daylight-saving transition falls inside the span. On March 14, 2027, clocks in America/New_York skip forward at 2:00 AM, so the wall-clock gap between 01:30 and 03:30 that day is 2 hours, but only 1 hour of real time actually passed. The calculator flags this difference instead of silently returning the wall-clock number.

Common mistakes

• Forgetting to confirm "end is next day" for an overnight span, which the calculator will not silently guess for you.
• Using clock mode across a daylight-saving change and expecting the real elapsed time to match the wall-clock subtraction.
• Entering a 12-hour time without AM/PM context; this calculator uses 24-hour time (13:00 is 1:00 PM) to remove that ambiguity entirely.

Limitations

This is a calendar and clock calculation, not a timekeeping or payroll record. It does not determine paid time, overtime eligibility, or any compliance or contractual outcome. For time zones, results depend on your browser's built-in time zone data, which is kept current by browser and operating system updates.