Read & write 24-hour time
Theory
A 24-hour time is four digits: hours from 00 to 23 and minutes, with no am or pm. Morning hours keep their number; evening hours are 12 more. Midnight is 00:00.
A 24-hour time is written as four digits: two for the hour and two for the minutes, with no am or pm.
The hours run from 00 at midnight up to 23, then start again at 00. There is no hour 24.
Morning hours keep their own number, so \(9\) am is 09. Afternoon and evening hours are 12 more, so \(9\) pm is 21. Always use two digits, so \(5\) minutes is written 05.
These landmark times are worth knowing.
| Time of day | 24-hour time |
|---|---|
| Midnight | 00:00 |
| One minute after midnight | 00:01 |
| Nine in the morning | 09:00 |
| Midday | 12:00 |
| Nine in the evening | 21:00 |
| Last minute of the day | 23:59 |
Writing a 24-hour time
- Morning? Keep the hour number and write it with two digits (9 becomes 09).
- Afternoon or evening? Add 12 to the hour (9 pm becomes 21).
- Write the minutes with two digits (5 becomes 05).
- No am or pm and no hour 24; midnight is 00:00.
Morning hours keep their number, with two digits each.
The time is 09:05.
| hour | \(=\) | \(9 + 12 = 21\) |
The time is 21:05.
The day starts at hour 00.
Midnight is 00:00 and one minute later is 00:01.
Eleven at night is hour 23, the last hour of the day.
Ten to midnight is 23:50.
Common pitfalls
Frequently asked questions
Why is a 24-hour time always four digits?
Two digits show the hour and two show the minutes, so the time is never confusing. \(9\) becomes 09 and \(5\) minutes becomes 05, giving 09:05.
Why does the clock never show 24:00?
The hours only go from 00 to 23. Once hour 23 ends, a whole day has passed and the clock restarts at 00:00, which is midnight.
How do I write an evening time?
Add 12 to the hour. Nine in the evening is \(9 + 12 = 21\), so five past nine at night is 21:05.
What is midnight in 24-hour time?
00:00. One minute after midnight is 00:01, and the last minute before the next midnight is 23:59.
Do I still use am and pm?
No. A 24-hour time never uses am or pm, because the hour number already tells you which half of the day it is in.