Time · Duration · Intervals
Time Duration
Calculator
Find time between two times, add or subtract durations, sum multiple time intervals, and convert between hours, minutes, and seconds.
—
Duration
—
Total Mins
Between
Mode
Time Between Two Times
Enter start and end times. Check "Overnight" if the end time is the next day.
Quick presets
Add or Subtract from a Time
Start with a time and add or subtract hours, minutes, and/or seconds.
Operation
:
:
Sum Multiple Durations
Add multiple time intervals together — great for summing task times, lap times, etc.
Convert Time Units
Enter a value and unit — get it expressed in all other time units.
Duration
—
Hours
—
Minutes
—
Total Seconds
—
Total Minutes
—
Total Hours
—
Days + Hours
—
Duration Breakdown
Time Duration Calculations
Time duration calculations are used in payroll, project management, sports timing, cooking, travel planning, and everyday scheduling. This calculator handles hours:minutes:seconds arithmetic including overnight spans and unit conversions.
How Time Arithmetic Works
Duration = End − Start (in total seconds)
Overnight: add 24 hours to end if end < start
HH:MM:SS format: hours = total_seconds ÷ 3600
minutes = (total_seconds % 3600) ÷ 60
seconds = total_seconds % 60
Unit conversions:
1 min = 60 sec 1 hr = 3,600 sec
1 day = 86,400 sec 1 week = 604,800 sec
How do you calculate time duration across midnight?
When a shift starts before midnight and ends after midnight (e.g. 10pm–6am), the end time appears earlier than the start. To handle this: if end time < start time, add 24 hours (86,400 seconds) to the end before subtracting. Example: 22:00 to 06:00 → 06:00 + 24:00 = 30:00 → 30:00 − 22:00 = 8 hours. The "Overnight" checkbox in this calculator does this automatically.
How do you add time in HH:MM:SS format?
Convert everything to seconds first, add, then convert back. For example: 1:30:45 + 2:45:20 = (1×3600+30×60+45) + (2×3600+45×60+20) = 5,445 + 9,920 = 15,365 seconds = 4 hours, 16 minutes, 5 seconds (15,365 ÷ 3600 = 4h rem 965; 965 ÷ 60 = 16m rem 5s). Always convert to a base unit, operate, then convert back.
What is the difference between duration and time?
Time is a point on the clock (e.g. 3:00 PM). Duration is a span or interval (e.g. 2 hours 30 minutes). Time is absolute; duration is relative. You can add two durations (1h + 2h = 3h) but not two clock times (3pm + 5pm ≠ 8pm). You can subtract two times to get a duration (5pm − 3pm = 2h duration) or add a duration to a time to get a new time (3pm + 2h = 5pm).