Time on the 24-Hour Clock (Military Time)
Summary
To write time in the 24-hour system, always specify both the hour and the minute, and include the leading zero for single-digit hours. Use numerals instead of words. Four digits should always be shown.
- Our flight landed at 05:45 in Cancun.
A colon is generally used as a separator between hours and minutes.
- The operation commenced at 1830 hours.
When the word hours is used, the colon is omitted.
Pronounce the leading zero as oh or zero (oh-five-forty-five or zero-five-forty-five). Whole hours are referred to using the word hundred: ten-hundred for 1000 hours, not thousand hours. Similarly, read 18:00 as eighteen-hundred.
Midnight is 00:00 at the start of the day and 24:00 at the end of the day.
The 24-hour clock
The 24-hour clock or the 24-hour system of time, often called military time in the United States, shows the day divided into 24 hours that run from midnight to midnight (00:00 to 24:00), instead of two 12-hour periods (midnight to noon and then noon to midnight), as on the 12-hour clock. The first hour on the 24-hour clock is denoted by the numerals 00 and the last hour by 23. Minutes are shown running from 00 to 59; seconds may or may not be shown. The numbers for time are always written in numerals, not words.
- Midnight = 00:00
zero hours, or start of day
- 12:30 a.m. = 00:30
half an hour after midnight, or 30 minutes from start of day
- 1:00 a.m. = 01:00
- 6:30 a.m. = 06:30
- 12:30 p.m. = 12:30
- 4:30 p.m. = 16:30
16 hours and 30 minutes from start of day
- 8:15 p.m. = 20:15
20 hours and 15 minutes from start of day
- 11:59 p.m. = 23:59
23 hours and 59 minutes from start of day
- Midnight = 24:00
24 hours since start of day, so the end of the day
In the 24-hour system, four digits are always shown. The leading zero is included for single-digit hours (0600 hours), and minutes are also always specified.
- The train leaves at 06:00 every day.
- It arrives in Berlin at 18:25 the same day.
- Your flight has been rescheduled to 2000 hours.
12-hour vs. 24-hour system
A disadvantage of using the 12-hour system is that it can be confusing—for example, the numerals 06:30 can refer to a time either in the morning or in the evening, a.m. or p.m. Confusion can result if these abbreviations are read or heard incorrectly. The 24-hour system is less ambiguous, with 06:30 indicating a time in the morning, and 18:30 clearly referring to a time in the evening.
Thus, the 24-hour system is generally preferred in military, hospital, research, and transit settings, where confusion between a.m. and p.m. could result in dangerous or expensive mistakes. In scientific writing as well, where clarity is important, the 24-hour clock is generally preferred over the 12-hour clock.
- At 14:35, the cells began to multiply.
- The first meteorite was detected at 04:33.
- Prepare for debriefing at 2030 hours.
Many countries officially follow the 24-hour system of time. But in many English-speaking countries, like the United States, the 12-hour clock is most often used in daily communication.
Use of hours
In the 24-hour system (or military time), the word hours is used after the numerals for time.
- The captain sounded general quarters at 0625 hours.
- Our operation commenced at 1900 hours.
- Farley was declared dead at 1425 but then revived at 1429 hours.
Colon as separator
The colon is used as a separator between hours and minutes when the word hours is omitted. We see this usage in timetables at airports, bus stops, and train stations.
- Departure is at 15:45.
- The bus from Frankfurt will arrive at 09:25 today.
- Your portal to Andromeda will open at 20:00 on May 21.
How to pronounce
To read aloud 24-hour-clock time, pronounce the leading zero as oh or zero. Use the word hundred to refer to whole hours. Always indicate both the hour and the minute.
- The bell rang at 08:30.
oh-eight-thirty or zero-eight-thirty
- The squad reached Egypt at 1615 hours.
sixteen-fifteen hours
- Our flight is at 20:00 today.
twenty-hundred
- General quarters sounded at 1900 hours.
nineteen-hundred hours
- The squadron took off from Cancun at 0930 and landed in Austin at 1000 hours.
zero-nine-thirty and ten-hundred hours (not thousand hours)
For times other than whole hours, the word hundred is omitted and oh or zero is used instead.
- 06:05 = oh-six-oh-five (also zero-six-zero-five)
- 18:09 = eighteen-oh-nine
- 06:00 = oh-six-hundred or zero-six-hundred
- 18:00 = eighteen-hundred
- 06:30 = oh-six-thirty or zero-six-thirty
- 18:35 = eighteen-thirty-five
- 24:00 = twenty-four-hundred
The first hour of the day is written and read aloud as follows.
- 00:00 = zero-hundred (or zero hours)
- 00:01 = zero-oh-one
- 00:25 = zero-twenty-five
- 00:30 = zero-thirty
- 00:59 = zero-fifty-nine
- 01:00 = zero-one-hundred (or oh-one-hundred)
Midnight: 00:00 or 24:00?
Both 00:00 and 24:00 refer to midnight on the 24-hour clock. Within a given time frame, 00:00 indicates the start of a day, while 24:00 indicates the end of a day.
- Let’s have a weekly call from 22:30 to 24:00 on Tuesdays.
from 10:30 p.m. to midnight of the same day
- From 0000 to 0200 hours, we dug a ditch in the pouring rain.
at the start of a day
Some style manuals recommend avoiding time frames with midnight altogether to eliminate confusion. They suggest using 00:01 and 23:59 instead of 00:00 or 24:00 to refer to the start and end of a day.
- Submit your applications by 23:59 on May 12, 2093.
Makes it clear that the deadline is at the end of the given day.
- The portal remains open from 0001 to 2359 hours on weekdays.
- Your three-day leave begins at 00:01 on February 29, 3044.
Daily reset: Times after midnight (24:00)
On the 24-hour clock, the latest time is usually 24:00. After this, the day resets, and the next minute is 00:01.
- Farley’s experiment began at 23:35 and ended abruptly at
24:15/00:15, when the jar exploded. - I was in a meeting last night from 22:30 to
25:00/01:00.
Some international publications and media styles allow for times like 24:05 to show the continuation of an event beyond midnight. Such usage is rare; if you encounter it as an editor, check your client’s house style.