Time Duration Calculator
Find the elapsed time between two clock times, chain an add or subtract on a duration, sum a whole list of intervals, or convert freely between seconds, minutes, hours, days, and weeks — one duration toolkit, four modes.
08h 30m
Duration
510
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
Duration
08:30:00
8h 30m 0s
8
Hours
30
Minutes
30,600
Total Seconds
510.00 min
Total Minutes
8.5000 hr
Total Hours
0d 08h
Days + Hours
Time Duration Breakdown
Start Time
09:00
End Time
17:30
Duration
08:30:00
HH:MM:SS
Total Seconds
30,600
seconds
Total Minutes
510.00
minutes
Total Hours
8.5000
decimal hours
Overnight?
No
In Days
0d 08h
Time Duration Calculations
Duration math takes a few different shapes depending on what you actually know: sometimes you have two clock times and need the gap between them, sometimes you have a duration you need to adjust up or down, sometimes you have a whole list of intervals to total, and sometimes you just need the same length of time expressed in a different unit. This calculator keeps all four of those as clearly separated tabs instead of forcing every question through one input shape.
🧮 How Time Arithmetic Works
Duration = End − Start (in total seconds)Overnight (checked): End total seconds += 24 × 3,600 before subtractingHH:MM:SS = ⌊seconds ÷ 3600⌋ : ⌊(seconds % 3600) ÷ 60⌋ : (seconds % 60)Unit constants: 1 min = 60s · 1 hr = 3,600s · 1 day = 86,400s · 1 week = 604,800sEvery tab on this page reduces its inputs down to a single total-seconds figure, applies the relevant operation (subtract, add/subtract, sum, or unit-scale), then converts that figure back into whichever display format you need — HH:MM:SS, decimal hours, or another unit entirely.
— FAQ