Calendar desk
Time Duration Calculator
Calculate elapsed time between two clock times, including overnight spans.
Time Duration Calculator: Compare two clock times to obtain total minutes and decimal hours, allowing an earlier end time to mean the following day. Matching start and end times give zero. The comparison assumes a regular clock day and has no dates or time zones, so it cannot correct for daylight-saving changes or multi-day spans. Runs 100% locally in your browser with zero server file uploads.
- Category
- Calculators
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Duration
—
- Total minutes
- —
Duration = end time − start time; an earlier end rolls into the next day- Times use a 24-hour clock and are interpreted on the same day unless the end is earlier.
- No date, time zone, or daylight-saving adjustment is applied.
Formula and worked example
Duration = end time − start time; an earlier end rolls into the next day
A worked example with sample values:
| Inputs | |
|---|---|
| Start time | 09:00 |
| End time | 17:30 |
| Results | |
|---|---|
| Duration | 8.5 hours |
| Total minutes | 510 |
Clock-minute formula and overnight example
Let S = 60 × start hour + start minute and E = 60 × end hour + end minute. If E < S, replace E with E + 1440. Duration in minutes T = E − S, and decimal hours H = T ÷ 60. Each input uses a 24-hour clock with valid hours from 00 to 23 and minutes from 00 to 59.
For 23:30 to 01:00, S = 23 × 60 + 30 = 1410 and E = 60. Since 60 < 1410, the adjusted end is 60 + 1440 = 1500. T = 1500 − 1410 = 90 minutes; H = 90 ÷ 60 = 1.5 hours. Those are the widget's two outputs for this overnight pair.
Wall-clock duration and elapsed duration
NIST's account of daylight saving (https://www.nist.gov/pml/time-and-frequency-division/popular-links/daylight-saving-time-dst) explains how local clocks can skip or repeat an hour. This calculator's ordinary 1440-minute rollover does not model either event. It also assumes both readings refer to the same clock basis.
Decimal hours are fractions of an hour, so the example's 1.5 means one hour and thirty minutes. The minutes output is useful when a timesheet or task log expects an integer duration. Breaks are not deducted automatically; for a same-day work interval with an unpaid break, use the work hours calculator. For a flight or a multi-day journey, retain full departure and arrival timestamps instead of reducing them to these two clock fields.
How to use it
- Enter the starting clock time in 24-hour form.
- Enter the ending time; an earlier value is treated as the next day.
- Calculate total minutes and decimal hours, then account separately for any breaks or clock changes.
Privacy & limitations
Dates, times and results stay in your browser. No inputs are uploaded.
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Frequently asked questions
How does the calculator recognise an overnight interval?
If the end clock time is earlier than the start, it adds one 24-hour day to the end before subtracting. There is no explicit date field to identify a longer interval.
Do equal start and end times mean a full day?
No. Equal times return zero because only an earlier end triggers the overnight adjustment. This widget cannot express a full 24-hour span or several days using identical clock values.
Can I compare times in different cities or on a DST-change night?
Not directly. The inputs have no zone, UTC offset or date. Convert actual timestamps to a common basis when their zones differ or a daylight-saving change skips or repeats an hour.
Embed this tool
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