How Time Duration Calculation Works
This tool calculates the time difference between two given times by first converting both into 24-hour format for consistency, then breaking each down into total seconds since midnight (hours × 3600 + minutes × 60 + seconds).
It subtracts the start time's seconds from the end time's to get the raw difference in seconds. If the result is negative (indicating an overnight duration), it adds 86,400 seconds (24 hours) to correct it.
Finally, it converts the total seconds back into hours (dividing by 3,600), minutes (remainder divided by 60), and seconds (final remainder), giving the duration in an easy-to-read HH:MM:SS format along with separate hour/minute/second breakdowns.
The calculation handles AM/PM times automatically and works for any same-day or overnight duration.
The calculator first converts both times to 24-hour format for consistent calculation.
6:40:55 PM → 18:40:55 (PM = +12 hours)
Each time is converted to total seconds since midnight using the formula:
Total Seconds = (Hours × 3600) + (Minutes × 60) + Seconds
(9 × 3600) + (30 × 60) + 40 = 34,240 seconds
End Time (6:40:55 PM):
(18 × 3600) + (40 × 60) + 55 = 67,255 seconds
Subtract start time from end time:
If result is negative (overnight duration), add 86,400 seconds (24 hours)
Break down the total seconds:
Remaining: 33,015 - 32,400 = 615 seconds
Minutes: 615 ÷ 60 = 10 minutes (600 seconds)
Seconds: 615 - 600 = 15 seconds
The duration is presented in multiple formats:
Readable Format: 9 hours, 10 minutes, and 15 seconds
Alternative Formats:
- 9.17 hours
- 550 minutes
- 33,015 seconds