Your times remain on this device
Clock times, breaks and durations are processed locally and are not sent to a server or added to the URL.
Clock and duration arithmetic
Time and hours calculator
Compare two clock times, add or subtract a duration, adjust one interval for a break, or convert a duration into normalized hours, minutes and seconds.
Calculate time
Calculated time
Clock calculations are exact to the entered second. Decimal hours are rounded only for display.
Need a full timesheet?
To total several workdays, subtract breaks, handle night shifts or estimate overtime, use the dedicated work hours calculator.
How the calculations work
Each clock time is converted to the number of seconds since 00:00:00. Duration arithmetic then uses whole seconds, without time zones or daylight-saving rules.
Difference
duration = end - start (+ 24 h when crossing midnight)The interval is inclusive of neither endpoint; it measures elapsed time.
Worked hours
worked duration = gross interval - breakThe break is validated before subtraction so the result cannot be negative.
Decimal hours
decimal hours = total seconds / 3,600For example, 7 h 30 min equals 7.5 decimal hours.
Available modes
Time difference
Measure elapsed time on the same day or across midnight.
Clock adjustment
Add or subtract a duration and see the day offset.
Worked hours
Subtract an unpaid break from a shift.
Duration conversion
Normalize large minute or second values and show decimal hours.
Important limits
- This tool uses clock arithmetic only and does not apply time zones or daylight-saving changes.
- For legal payroll calculations, follow the rounding and break rules required in the relevant country or agreement.
- A crossing-midnight interval must be marked explicitly.
- Decimal hours are a representation of a duration, not a clock time.
Examples
Morning interval
08:30 to 12:45
4 hours 15 minutes
Night shift
22:00 to 06:30, crossing midnight
8 hours 30 minutes
Worked hours
09:00 to 17:30 with a 30-minute break
8 hours = 8.0 decimal hours
Normalize minutes
1 hour, 90 minutes, 30 seconds
2 hours 30 minutes 30 seconds
Frequently asked questions
Can the calculator handle overnight work?
Yes. Enable the crossing-midnight option so the end time is treated as occurring on the following day.
What are decimal hours?
They express a duration as a decimal number of hours. Thirty minutes equals 0.5 hour and fifteen minutes equals 0.25 hour.
Does the calculator account for daylight saving time?
No. It performs abstract 24-hour clock arithmetic without a date or time zone.
Can minutes exceed 59 in conversion mode?
Yes. Conversion mode normalizes large minute and second values into hours, minutes and seconds.
Technical references
- BIPM - SI Brochure
Reference for the SI second and time units.
- ISO - Date and time format
Overview of the international date and time representation standard.
- MDN - input type=time
Browser behavior for native time inputs.