24-Hour Time and Military Time: How to Read and Convert It
How to convert between 12-hour and 24-hour time, how military time is written and spoken, what 0000 and 2400 mean, and how Zulu time and zone letters work.
The 24-hour clock numbers the hours of the day from 00 to 23, so there is no a.m. or p.m. To convert a p.m. time to 24-hour time, add 12 to the hour (3:15 p.m. → 15:15); to go back, subtract 12 from any hour of 13 or more (21:40 → 9:40 p.m.). The two exceptions are the 12 o’clock hours: 12 a.m. becomes 00, and 12 p.m. stays 12.
“Military time” is the same 24-hour clock written without the colon (1515) and usually spoken as a four-digit number, often followed by a letter that names the time zone.
Full 12-hour to 24-hour conversion table
| 12-hour clock | 24-hour clock | Military (written) | Military (spoken) |
|---|---|---|---|
| 12:00 a.m. (midnight) | 00:00 | 0000 | zero hundred / zero zero hundred |
| 1:00 a.m. | 01:00 | 0100 | zero one hundred |
| 2:00 a.m. | 02:00 | 0200 | zero two hundred |
| 3:00 a.m. | 03:00 | 0300 | zero three hundred |
| 4:00 a.m. | 04:00 | 0400 | zero four hundred |
| 5:00 a.m. | 05:00 | 0500 | zero five hundred |
| 6:00 a.m. | 06:00 | 0600 | zero six hundred |
| 7:00 a.m. | 07:00 | 0700 | zero seven hundred |
| 8:00 a.m. | 08:00 | 0800 | zero eight hundred |
| 9:00 a.m. | 09:00 | 0900 | zero nine hundred |
| 10:00 a.m. | 10:00 | 1000 | ten hundred |
| 11:00 a.m. | 11:00 | 1100 | eleven hundred |
| 12:00 p.m. (noon) | 12:00 | 1200 | twelve hundred |
| 1:00 p.m. | 13:00 | 1300 | thirteen hundred |
| 2:00 p.m. | 14:00 | 1400 | fourteen hundred |
| 3:00 p.m. | 15:00 | 1500 | fifteen hundred |
| 4:00 p.m. | 16:00 | 1600 | sixteen hundred |
| 5:00 p.m. | 17:00 | 1700 | seventeen hundred |
| 6:00 p.m. | 18:00 | 1800 | eighteen hundred |
| 7:00 p.m. | 19:00 | 1900 | nineteen hundred |
| 8:00 p.m. | 20:00 | 2000 | twenty hundred |
| 9:00 p.m. | 21:00 | 2100 | twenty-one hundred |
| 10:00 p.m. | 22:00 | 2200 | twenty-two hundred |
| 11:00 p.m. | 23:00 | 2300 | twenty-three hundred |
Minutes never change in the conversion: 4:07 p.m. is 16:07, and 00:59 is 12:59 a.m.
Quick mental conversion
- Morning (a.m.): the hour is the same, padded to two digits. 9:20 a.m. → 09:20. Only 12 a.m. changes, to 00.
- Afternoon and evening (p.m.): add 12. 1 p.m. → 13, 6 p.m. → 18, 11 p.m. → 23. Only 12 p.m. does not change.
- 24-hour to 12-hour: if the hour is 13 or more, subtract 12 and say p.m. If it is 12, say p.m. If it is 00, say 12 a.m. Otherwise it is a.m.
A shortcut many people use for the subtraction: subtract 2 from the last digit of the hour, ignoring the tens. 17 → 7 − 2 = 5 p.m.; 19 → 9 − 2 = 7 p.m. It works for 13 through 19; for the last four hours it is easier to remember 20 = 8 p.m., 21 = 9 p.m., 22 = 10 p.m., 23 = 11 p.m.
How military time is written and spoken
In military and some emergency-service usage, the colon is dropped and the time is always four digits: 0630, 1745, 2210. Leading zeros are kept, and they are spoken.
- 0600 is said “zero six hundred” or, informally, “oh six hundred”. The word “hours” is often added: “zero six hundred hours”.
- 1730 is “seventeen thirty” — the “hundred” is used only when the minutes are zero.
- 0015 is “zero zero fifteen”.
- 2000 is “twenty hundred”, not “two thousand”.
Civilian 24-hour usage in most countries keeps the colon (or a period, in some languages) and reads the time as hours and minutes: 17:30 is “seventeen thirty”. The underlying numbers are identical; “military time” is mainly an American term for the 24-hour clock.
0000 or 2400?
Midnight is the one point that can be written two ways:
- 00:00 (
0000) is the start of a day. 00:00 on 23 October is the moment 22 October ends. - 24:00 (
2400) is the end of a day. 24:00 on 22 October is the same instant as 00:00 on 23 October.
The U.S. National Institute of Standards and Technology (NIST) suggests exactly this convention as a way to avoid the ambiguity of “12 a.m.” — 0000 for midnight at the beginning of a day and 2400 for the end. In practice, clocks and most software never display 24:00; they roll from 23:59 to 00:00. You will see 24:00 mainly in schedules (“open 07:00–24:00”) and in some documents where the end of a day needs to be explicit. The ISO 8601 standard covers this too; see ISO 8601 Date and Time Format.
Some organizations avoid both and write 2359 for “end of the day”, which sidesteps the question at the cost of one minute. The same trick is common for deadlines; see 12 AM or 12 PM?.
Zulu time and military time zone letters
Military time is normally qualified with a single letter that identifies the time zone. The letters come from the NATO phonetic alphabet and follow whole-hour offsets from UTC:
| Letters | Phonetic names | Offset |
|---|---|---|
| Z | Zulu | UTC±0 |
| A–I, K–M | Alpha to India, Kilo to Mike | UTC+1 to UTC+12 |
| N–Y | November to Yankee | UTC−1 to UTC−12 |
| J | Juliet | the observer’s local time |
Zulu (Z) is the most important one: it means UTC. 1400Z is 14:00 UTC, whatever the local time of the reader. Aviation, weather services and maritime traffic all use Zulu time so that everyone working across zones refers to the same clock. The same “Z” appears at the end of machine timestamps such as 2026-10-22T14:00:00Z.
The other letters describe fixed offsets, not civil time zones with daylight saving rules. Romeo (R) is UTC−5, which matches U.S. Eastern Standard Time but not Eastern Daylight Time; in summer, New York is on UTC−4, which is Quebec (Q). Juliet (J) is skipped in the sequence and conventionally means “local time, wherever the observer is”.
The full list, each with a live clock, is on the military time zones page; for example, Zulu, Romeo and Alpha.
Converting a Zulu time to local time
Add the local UTC offset to the Zulu time, rolling over midnight if necessary:
- 1400Z in New York in October (UTC−4): 14 − 4 = 10:00 local.
- 2230Z in Tokyo (UTC+9): 22:30 + 9 h = 07:30 local, the next day.
- 0300Z in Los Angeles in January (UTC−8): 03 − 8 = −5, so add 24 → 19:00 local, the previous day.
The date change is the most common error. For anything that matters, a time zone converter handles the offsets and daylight saving dates for you.
Who uses the 24-hour clock
The 24-hour clock is the standard written form in much of the world and in international contexts: aviation, railways, the military, hospitals, and computing. In many countries it is also the default on phones, timetables and official documents.
The 12-hour clock remains common in everyday speech and writing in a number of English-speaking countries, including the United States, Canada (outside Quebec), Australia and New Zealand, as well as in some other countries. Even there, 24-hour time is usual in fields where a misread a.m./p.m. is costly. Usage is rarely all-or-nothing: in many places people write 18:00 but say “six o’clock”.
Common mistakes
- Writing 12:30 for half past midnight. In 24-hour time that is 00:30; 12:30 is half past noon.
- Adding 12 to 12 p.m. Noon is 12:00, not 24:00.
- Dropping the leading zero in military time. “630” is ambiguous in a log; write
0630. - Assuming a letter equals a civil time zone. Military letters are fixed offsets and do not change for daylight saving time.
Sources
Dates, offsets and astronomical times quoted here are computed with the same code that powers the site's tools — see data sources and methods. Found an error? Tell us.