The **24-hour clock** is one of the ways we can tell the time, so let's look at how we can write the time using the 24-hour clock correctly.

There are** 24 hours in a day** and this system simply uses the number of the hour in the day to tell the time.

After 12:00 pm on the 24-hour clock, we continue counting upwards from 13 (1 pm) until we reach 24 (12 midnight).

For example - 11 am is the 11th hour of the day, or 3 pm is the 15th hour (we count up from 12 pm to 1 pm (13th hour) 2 pm (14th hour) to 3 pm (15th hour).

Alternatively, you can add 12 to the hours to work out the time after 12 noon.

For example, **04:00** (+12) = **16:00** and **07:00** (+12) = **19:00**

The first thing we must remember is the** ****24 hour clock time**** always uses 4 numbers** separating the hours from the minutes with a** :** sign.

If you look at the 24-hour example below, we see that each of these uses **4 numbers**. If the time is early in the morning, as in the example, we **must **include a 0 before the number 7, so we meet the 4 number rule!

7.35 a.m. is 07:35

7.35 p.m. is 19:35

You may notice that when we write the time using the 24-hour clock, we **don't write am or pm**. This is because we know that anything between 00:00 and 11:59 (the first 12 hours) refers to a the morning, and 12:00 - 23:59 is the afternoon/evening.

Once we know these basic rules for writing the time using the 24-hour clock, we can start to do more advanced things, like adding and subtracting time... let's give this a go!

**Example**

What 24-hour clock time is 46 minutes after 7.35 p.m.?

**Answer**

We start on the hour at 7.00 p.m. and then add 46 minutes and 35 minutes from the question.

35 + 46 = 81 minutes.

81 minutes is 1 hour (60 minutes) and 21 minutes.

1 hour and 21 minutes after 7.00 p.m. is 8.21 p.m.

8.21 p.m. is **20:21 **in 24 hour clock time.