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Time Utility

Time Duration Calculator

Determine the exact duration between two dates and times down to hours, minutes, and seconds.

Start & End parameters

Start Time

End Time

Enter valid parameters to compute duration.
Time Math

How to Calculate
Time Duration

Calculating time duration is the process of finding the elapsed time between a starting event and an ending event.

24-Hour System

Converting times to 24-hour military format simplifies subtraction and prevents errors when calculations span PM to AM hours.

Midnight Boundary

Calculations crossing midnight are resolved by adding 24 hours to the end time before performing standard subtraction.

Precise Subtraction

Subtract minutes first. If the end minutes are less than start minutes, borrow 60 minutes from the hours column.

The Basic 12-Hour vs. 24-Hour Conversion

To calculate duration manually, it is easiest to convert standard 12-hour clock times (AM/PM) into 24-hour military format:

  • AM times: Keep the hour exactly the same (except 12:00 AM, which becomes 00:00).
  • PM times: Add 12 to the hour (except 12:00 PM, which stays 12:00).

Time Conversion Quick Cheat Sheet:

  • • 12:00 AM (Midnight) ➔ 00:00
  • • 08:30 AM ➔ 08:30
  • • 12:00 PM (Noon) ➔ 12:00
  • • 05:45 PM ➔ 17:45

How the calculation works

Duration is the later timestamp minus the earlier one.

Minutes = end − start, then split into hours and minutes

Crossing midnight adds 24 hours before subtracting.

Worked example: 09:15 to 13:45

  1. From 09:15 to 13:15 is 4 hours.
  2. The extra 30 minutes make 4 hours 30 minutes.
  3. Decimal hours = 4.5.

Durations starting at 09:15

EndDuration
11:152 h 00 m
13:454 h 30 m
18:008 h 45 m

Frequently asked questions

How long is 09:15 to 13:45?▼
4 hours 30 minutes.
What is that in decimal hours?▼
4.5.
How do you cross midnight?▼
Add 24 hours to the end time, then subtract.