Article — Military Time Converter
Military time conversion explained
- What military time is
- How to convert 12-hour to military time
- How to convert military time to 12-hour
- The two confusing boundaries: 0000 and 1200
- Who uses military time outside the military
- Zulu time, UTC, and the NATO time zone letters
- How to pronounce military time correctly
- Mistakes to avoid when reading military time
Military time is a 24-hour clock that runs from 0000 (midnight) to 2359 (11:59 PM). To convert 12-hour time to military time, add 12 to any PM hour except 12 PM, and turn 12 AM into 00. The minutes never change. 3:45 PM = 1545. 12:00 AM = 0000. 12:00 PM = 1200.
The format dates to NATO's Allied Communication Publication 121 (ACP 121), which standardizes how military forces write and speak time. The same clock is used by the FAA for aviation, by the National Weather Service for weather observations, by every US hospital for medication orders, and by most railways outside the United States.
What military time is
Military time uses four digits to express any time of day uniquely. The first two are the hour (00 to 23), the last two are the minute (00 to 59). There is no colon, no AM, no PM. Each four-digit string maps to exactly one time, so a written or spoken value cannot be misread.
The format solves a practical problem. With AM/PM, the time "7:00" depends on context. With 24-hour notation, 0700 is morning and 1900 is evening. There is no overlap. The US Naval Observatory, which serves as the official US time authority, uses 24-hour time on all its public time displays for the same reason.
The 24-hour clock is older than the 12-hour clock by about a thousand years. Ancient Egyptian and Babylonian astronomers divided the day into 24 hours by 1500 BCE. The 12-hour clock with AM/PM became common only in medieval Europe, when mechanical church clocks needed simpler dials with a single 12-hour rotation.
How to convert 12-hour to military time
The rules depend on whether the time is AM or PM and on whether the hour is 12.
- 1:00 AM to 11:59 AM: pad the hour with a leading zero. 9:30 AM = 0930.
- 12:00 AM (midnight): use 0000 (or write 2400 for the very end of the previous day).
- 12:00 PM (noon): use 1200 unchanged.
- 1:00 PM to 11:59 PM: add 12 to the hour. 3:00 PM = 15:00 = 1500. 9:45 PM = 21:45 = 2145.
The minutes are always copied through. The AM/PM marker disappears entirely. That is the whole rule set — four cases.
How to convert military time to 12-hour
The reverse direction is the same pattern run backward.
- 0000 to 0059: convert to 12:MM AM. 0030 = 12:30 AM.
- 0100 to 1159: drop the leading zero and append AM. 0830 = 8:30 AM.
- 1200 to 1259: keep the hour as 12 and append PM. 1245 = 12:45 PM.
- 1300 to 2359: subtract 12 from the hour and append PM. 1815 = 6:15 PM.
0700 = 7 AM 1300 = 1 PM1500 = 3 PM 1700 = 5 PM1900 = 7 PM 2100 = 9 PMThe two confusing boundaries: 0000 and 1200
Midnight and noon trip almost everyone the first time. The 12-hour clock numbers them inconsistently: 12 AM is midnight (the start of the day), 12 PM is noon (the middle of the day). There is no widely used 0 AM or 0 PM. So 12:00 AM converts to 0000, while 12:00 PM converts to 1200. The difference is twelve hours, but the 12-hour numbers look almost identical.
Some scheduling software writes midnight as 2400 instead of 0000 to disambiguate "end of Tuesday" from "start of Wednesday." Most military and aviation use prefers 0000 paired with the calendar date, which removes the ambiguity by stamping the day alongside the time.
It is a very common mistake: 12 PM is noon, not midnight. The mnemonic is that AM (ante meridiem) means "before noon" and PM (post meridiem) means "after noon," but noon itself sits exactly at the boundary. The Library of Congress and US Government Publishing Office style guides recommend writing "12 noon" or "12 midnight" in any document where the meaning could be misread.
Who uses military time outside the military
Hospitals are the largest civilian users in the United States. The Joint Commission, which accredits about 80 percent of US hospitals, recommends 24-hour notation for medication administration records and shift handovers, because a 7:00 PM dose written as "7:00" could be administered twelve hours late. The US Veterans Health Administration mandates 24-hour notation across all its facilities.
Aviation runs on UTC (Zulu time) using 24-hour notation. Flight plans, weather reports (METAR), and air traffic control transmissions are all in HHMMZ form. Outside the United States, railway timetables, public broadcast schedules, and most government documents use 24-hour notation as the default. Europe in particular has used 24-hour time as the everyday written norm since the 1960s.
Zulu time, UTC, and the NATO time zone letters
Zulu time is the military name for Coordinated Universal Time (UTC). The letter Z is the NATO phonetic alphabet code for the time zone at UTC+0, which is what Britain calls Greenwich Mean Time outside daylight saving. A weather observation taken at 1500 GMT is reported as 1500Z. A flight plan filed for 2030 UTC reads 2030Z.
NATO uses single-letter codes for each one-hour offset from UTC. Z is UTC+0, A is UTC+1, and the letters run through the alphabet (skipping J, which means "local time," and I to avoid confusion with the digit 1). The eastern offsets go A, B, C, D, E, F, G, H, K, L, M (UTC+12). The western offsets go N, O, P, Q, R, S, T, U, V, W, X, Y (UTC-12).
How to pronounce military time correctly
The conventions are old and unbreakable. Whole hours end in "hundred," never "thousand": 1500 is "fifteen hundred," 1800 is "eighteen hundred," 2200 is "twenty-two hundred." Times with minutes drop the word "hundred" and read the four digits in pairs: 1545 is "fifteen forty-five," 1830 is "eighteen thirty." Times with a single-digit minute keep the zero: 1505 is "fifteen oh-five."
Zero-padded hours are spoken with a leading "zero": 0730 is "zero seven thirty," not "seven thirty." Midnight (0000) is conventionally spoken as "midnight" rather than the awkward "zero hundred." The word "hours" is sometimes appended for formality: "Muster at zero six hundred hours" — but soldiers in routine conversation drop it.
If you are new to 24-hour time, practice with the public schedule for any European railway. Deutsche Bahn, SNCF, and Trenitalia all post departures as 13:42 or 19:08 in everyday signage. A week of reading them and the conversion will be automatic.
Mistakes to avoid when reading military time
The most common mistake is forgetting that 12:00 AM is 0000, not 1200. The second most common is forgetting that 12:00 PM is 1200, not 2400. Both errors send the converted time twelve hours off. The cure is to remember that the AM/PM number wraps from 11 to 12 at the boundary, while the 24-hour number wraps from 23 to 00 at midnight only.
The other recurring mistake is reading the four digits as a single number rather than as hour-minute pairs. 1545 is not "one thousand five hundred forty-five." It is fifteen forty-five — three o'clock in the afternoon plus 45 minutes. Reading the digits as a number is the giveaway that a civilian has not yet internalized the format.