Add and subtract time
Total several positive and negative durations.
Time Duration Calculator
Find the exact time between two clock times, including overnight shifts, dates, and unpaid breaks. Everything stays in your browser.
How the duration is calculated
Clock times are converted to integer seconds. The calculator subtracts the start from the end, adds 24 hours only when Ends next day is selected, then subtracts a validated break. If both dates are present, calendar-day boundaries replace the overnight option.
9:00 AM5:30 PM
Worked examples
9:00 AM to 5:30 PM: 17:30 − 09:00 = 8 hours 30 minutes.
10:15 PM to 6:45 AM: select Ends next day. The result is 8 hours 30 minutes.
Common mistakes
- Select Ends next day when the end clock time is earlier than the start.
- Enter both dates or leave both blank; one date cannot define an interval.
- A break cannot be longer than the gross duration.
Frequently asked questions
Does this calculator handle midnight?
Yes. Use 12:00 AM as midnight or 00:00 in a 24-hour clock, and select Ends next day when needed.
Are daylight-saving changes included?
No. This is a wall-clock calculator and does not apply named time-zone or DST rules.
Are my times uploaded?
No. Calculations run locally in your browser and no entered values are sent to us.
For a teaching-focused breakdown, use the elapsed time calculator or read how to calculate time duration.
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