The 24-Hour Clock Explained for Kids and Parents
By the TimesTable.co team · Updated · 4 min read
Train times, oven timers, phones and holiday itineraries all use the 24-hour clock, so children meet it long before they're taught it. It's actually simpler than the 12-hour clock once the idea clicks: every hour of the day gets its own number, and am and pm disappear. The tricky parts are the afternoon conversion, midnight and midday.
What is the 24-hour clock?
A day has 24 hours. The 12-hour clock goes round twice and uses am (before midday) and pm (after midday) to tell the two halves apart. The 24-hour clock simply keeps counting after 12: the hour after 12 is 13, then 14, all the way up to 23. At midnight it starts again at 00. Times are always written with four digits and a colon, like 09:15 or 18:40.
How do you convert 12-hour time to 24-hour time?
There are three simple rules:
- Morning (am): keep the hour and add a leading zero if needed. 7:30 am is 07:30; 10:45 am is 10:45.
- Afternoon and evening (pm, from 1 pm): add 12 to the hour. 3:15 pm is 3 + 12 = 15, so 15:15.
- The two 12s: midday stays as 12:00. Midnight becomes 00:00, and 12:30 am is 00:30.
The interactive clock set to 3:15 pm shows the rule working live: drag the hands or switch between am and pm, and the 24-hour time and "+ 12" rule update as you go.
What does the full conversion chart look like?
| 12-hour | 24-hour | 12-hour | 24-hour |
|---|---|---|---|
| 12 am (midnight) | 00:00 | 12 pm (midday) | 12:00 |
| 1 am | 01:00 | 1 pm | 13:00 |
| 2 am | 02:00 | 2 pm | 14:00 |
| 3 am | 03:00 | 3 pm | 15:00 |
| 4 am | 04:00 | 4 pm | 16:00 |
| 5 am | 05:00 | 5 pm | 17:00 |
| 6 am | 06:00 | 6 pm | 18:00 |
| 7 am | 07:00 | 7 pm | 19:00 |
| 8 am | 08:00 | 8 pm | 20:00 |
| 9 am | 09:00 | 9 pm | 21:00 |
| 10 am | 10:00 | 10 pm | 22:00 |
| 11 am | 11:00 | 11 pm | 23:00 |
How do you convert 24-hour time back to 12-hour time?
Do the rule backwards. If the hour is 13 or more, take away 12 and add "pm": 19:20 is 19 − 12 = 7, so 7:20 pm. If the hour is 12, it's just after midday, so 12:45 is 12:45 pm. If the hour is 00, it's just after midnight: 00:10 is 12:10 am. Anything from 01 to 11 is the same number in the morning.
Why do midnight and midday confuse children?
Because the 12-hour clock labels them oddly. 12:00 pm is midday, yet 12:59 pm is followed by 1:00 pm, not 13:00 pm. And midnight is "12 am", even though it's the very start of the morning. The 24-hour clock tidies this up: midday is 12:00 and midnight is 00:00. A handy check for children: in 24-hour time, a bigger hour means later in the day, with no exceptions.
What mistakes do children commonly make?
- Adding 12 to morning times: 9 am written as 21:00. Ask, "Is it morning? Then the hour doesn't change."
- Adding 12 to midday: 12:30 pm written as 24:30. Midday hours stay as 12.
- Dropping the leading zero: 6:05 am written as 6:05 rather than 06:05.
- Adding 10 instead of 12: 3 pm written as 13:00. Linking the rule to the 12 in "12 hours" helps it stick.
- Treating the time like a number: 14:50 plus 20 minutes becoming 14:70. There are only 60 minutes in an hour (12 lots of 5, which is why the 5 times table matters for clocks), so it's 15:10.
How can you practise the 24-hour clock at home?
- Switch a phone or oven clock to 24-hour time for a week and ask what it says in am and pm.
- Plan a pretend day out using a real train or bus timetable.
- Use the "day in the life" strip on the interactive clock: tap breakfast, lunch or bedtime and see each time in both forms.
- Test with the clock quiz and print some clock worksheets for extra practice.
If your child is still working on reading an analogue clock, start with how to teach a child to tell the time, then come back to the 24-hour clock. All the clock activities are together in the telling the time hub.
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Frequently asked questions
How do you convert pm times to the 24-hour clock?
Add 12 to the hour, from 1 pm onwards. 3:15 pm becomes 15:15 and 9 pm becomes 21:00. 12 noon to 12:59 pm stays as 12.
How do you convert 24-hour times back to am and pm?
If the hour is 13 or more, take away 12 and write pm: 17:40 is 5:40 pm. If it is 12, it is pm without any change; if it is 00, it is 12 am.
Is midnight 00:00 or 24:00?
Midnight is written 00:00 at the start of a new day. You may see 24:00 used for the end of a day, such as on timetables, but 00:00 is the everyday form.
Why do 24-hour times have four digits?
The hour always takes two digits and the minutes two digits, so 7:05 am is written 07:05. The leading zero keeps every time the same length.
Do you say "hundred hours" for 24-hour time?
Children in the UK usually just read the digits: 15:00 is "fifteen hundred" or "fifteen o'clock", and 15:30 is "fifteen thirty". "Hundred hours" is mostly used by the military.
When do children learn the 24-hour clock?
In England, children start using 12- and 24-hour clocks in Year 3 (age 7 to 8) and convert between analogue, 12-hour and 24-hour times in Year 4 (age 8 to 9).