24 hour time calculator

After entering a time in 24-hour format, this calculator lets you add and subtract a period to give a new time, also in 24 hour format. The 24 hour time format is also known as "military time".

For example, you could enter the time 15:00:00 (3 pm), then add 70 seconds to it which would give 15:01:10 ( 3:01 and 10 seconds pm).

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Hours Mins Secs
See also Calculate the difference between two 24-hour times


The calculator adds or subtracts input durations from the time in the top window. You first enter a time in 24 hour format For example 6:12:0 which is read as 6 hours 12 minutes and zero seconds. (6:12 am). After that you enter durations and add/subtract them from the time in the top window.

How it works

When a time is entered, it is internally converted to the number of seconds past midnight. When a duration is entered (For example: 2 hrs 8 mins) the duration is converted to seconds. The addition / subtraction is performed on the seconds and then the result formatted as a new 24 - hour time.

If the operation results in a time in another day, the number of days offset from the original time input is also shown.

For example if you enter 3:00:00 and then subtract 4 hours, it will show the result as

"23:00:00 Previous day"
meaning 11pm the day before the original time you entered.

A note about midnight

The calculator shows midnight as 00:00:00, and assumes that to be the beginning of a day. It will never display 24:00:00. So for example

12-hour readout

All time outputs are also displayed in 12-hour format below the main display window. It shows midnight as 12AM and is assumed to be the beginning of the day. To avoid confusion, mid-day is shown as "12:00:00 Noon" It never displays "12 PM". So for example

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