How the Time Duration Calculator works
Time-only Calculation converts each ClockTime to seconds since midnight. Date-and-time Calculation also converts each Civil Date to a day index. The tool subtracts the start from the end without consulting a timezone, DST rule, server, or current clock.
Examples you can reproduce
- 9:00 AM to 5:30 PM is 8 hours 30 minutes.
- 11:30 PM to 1:15 AM with Ends next day is 1 hour 45 minutes.
- Equal times are 0 by default, or exactly 24 hours with Ends next day.
- Turn on Include seconds to calculate values such as 23:59:59 to next-day 00:00:00 = 1 second.
Limits and assumptions
This is a Wall-clock Duration, not a timezone-aware elapsed duration. It does not adjust for daylight-saving transitions or leap seconds. Date inputs use the proleptic Gregorian calendar for years 1 through 9999.
Frequently asked questions
How is an overnight time calculated?
Ends next day adds exactly 86,400 seconds before subtraction. The policy is visible and shareable.
Does it account for DST?
No. Use this tool when the displayed local calendar values—not a zoned timestamp—are the facts you want to compare.
Is my input sent to a calculation server?
No. Calculation runs in your browser. Only an explicit Share action places normalized inputs in the URL fragment.