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Year 5 Maths Time

Read & write 24-hour time

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Theory

A 24-hour clock numbers the hours of the day from \(00\) to \(23\), so it never needs am or pm. Every time is written with four digits: two for the hours and two for the minutes. This Year 5 maths page shows how to read and write 24-hour times and how to tell what part of the day a time is in.

A 24-hour time has four digits: hours then minutes, e.g. \(\text{06:50}\). If the hour or the minutes are less than \(10\), write a 0 in front.

The day starts at midnight, \(\text{00:00}\). Midday is \(\text{12:00}\). The last minute of the day is \(\text{23:59}\); the next minute is \(\text{00:00}\) again, so a 24-hour clock never shows \(\text{24:00}\).

Hours \(00\) to \(11\) are before midday (morning, or night if very early). Hours \(12\) to \(23\) are after midday: afternoon, then evening, then night.

Say a 24-hour time as two numbers: \(\text{06:50}\) is "oh six fifty", \(\text{18:40}\) is "eighteen forty", \(\text{21:00}\) is "twenty-one hundred".

A day on a 24-hour timeline A timeline from midnight to midnight. Hours 00 to 23 are marked above the line, with the matching 12-hour numbers below. The first half is shaded as am and the second half as pm. Two red dots: A at 06:50 and B at 18:40. am (midnight to midday)pm (midday to midnight) 000306091215182100 123691236912 24-hour (top) and 12-hour (bottom) A 06:50 B 18:40
After midday the 24-hour number is \(12\) more than the 12-hour number: \(6\) pm is \(18\).
Clock showing quarter to five An analogue clock face with the hour hand nearly at 5 and the minute hand on 9, showing quarter to five. 123456789101112 in the afternoon
Quarter to five in the afternoon is \(\text{16:45}\).
Digital clock showing 22:10 A digital clock display showing 22:10. 22:10 twenty-two ten
\(\text{22:10}\) is ten past ten at night.

Rules for 24-hour time:

\[ \text{hh:mm}\ \ (00 \le \text{hh} \le 23,\ 00 \le \text{mm} \le 59) \]
hh mm , hours 00 to 23, minutes 00 to 59
\[ \text{midnight} = \text{00:00} \qquad \text{midday} = \text{12:00} \]
midnight =0000, midday =1200
\[ \text{pm hour} + 12 = \text{24-hour hour} \]
pm hour +12=24− hour hour
Always four digits. Ten past seven in the morning is \(\text{07:10}\), not \(\text{7:10}\).
No am or pm. The hour number already tells you the part of the day.

Writing a time in 24-hour time

  1. Decide if the time is before or after midday.
  2. Before midday: keep the hour (midnight hour is \(00\)).
  3. After midday: add \(12\) to the hour (except for the \(12\) o'clock hour).
  4. Write two digits for the hour and two for the minutes.
Example 1 — Morning
Write ten to seven in the morning in 24-hour time.
Solution

Ten to seven is \(6{:}50\), so \(\text{06:50}\).

Example 2 — Afternoon
Write twenty-five past one in the afternoon in 24-hour time.
Solution
\(1 + 12\)\(=\)\(13\)
1+12=13

\(\text{13:25}\).

Example 3 — Read a clock
Use the second diagram. Write the time in 24-hour time.
Solution
\(4 + 12\)\(=\)\(16\)
4+12=16

Quarter to five is \(4{:}45\) pm, so \(\text{16:45}\).

Example 4 — Part of the day
Is each time in the morning, afternoon, evening or night?
(i) \(\text{10:35}\)
(ii) \(\text{15:05}\)
(iii) \(\text{18:40}\)
(iv) \(\text{02:30}\)
Solution

(i) Morning
(ii) Afternoon
(iii) Evening
(iv) Night

Example 5 — Say it aloud
How do you say \(\text{07:05}\) and \(\text{21:00}\)?
Solution

"Oh seven oh five" and "twenty-one hundred".

Example 6 — Just after midnight
Write twelve minutes past midnight in 24-hour time.
Solution

The midnight hour is \(00\), so \(\text{00:12}\).

Example 7 — Possible or not?
Which of these cannot be a 24-hour time: \(\text{19:59}\), \(\text{00:30}\), \(\text{12:60}\)?
Solution

\(\text{12:60}\): the minutes only go up to \(59\).

Example 8 — Find the mistake
Ari wrote twenty past eight at night as \(\text{08:20}\). What should it be?
Solution
\(8 + 12\)\(=\)\(20\)
8+12=20

\(\text{08:20}\) is in the morning. At night it is \(\text{20:20}\).

Common pitfalls

Leaving out the zero. Write \(\text{06:50}\), not \(\text{6:50}\).
Forgetting to add 12. Eight at night is \(\text{20:00}\), not \(\text{08:00}\).
Writing 24:00. Midnight is \(\text{00:00}\).
Adding am or pm. 24-hour times do not use am or pm.

Frequently asked questions

How do you say 07:05?

"Oh seven oh five".

Why does 24-hour time not need am or pm?

The hour number already shows the part of the day: \(\text{08:00}\) is morning and \(\text{20:00}\) is evening.

How do I write a morning time?

Put a \(0\) in front of a one-digit hour: half past six in the morning is \(\text{06:30}\).

How do I know if a 24-hour time is in the afternoon?

The hour is \(12\) or more. \(\text{15:05}\) is in the afternoon.

How do you say 18:40?

"Eighteen forty".

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