0000 Military Time

0000 is 12:00 AM, midnight at the start of the day. On a 24-hour clock with a colon it is 00:00; in military style the colon goes and the four digits stand alone. The hour is 0 hours after midnight and 24 hours before the next one.

Midnight at the start of the day. Four zeros, said “zero hundred”. It is the one hour civilians write as 12 and the military writes as 0, which is why 12:15 AM becomes 0015 rather than 1215.

To read it, look at the first two digits: the hour is 00, which the 12-hour clock calls 12 AM. Keep the minutes. The last two digits are minutes and never change, so 0025 is 12:25 AM and 0050 is 12:50 AM.

Military to 12-hour. Split the four digits into hours and minutes, the hour is 00, which the 12-hour clock calls 12 AM. Keep the minutes. So 0015 becomes 12:15 AM and 0045 becomes 12:45 AM.

12-hour to military. 12 AM is the odd one out: write the hour as 00, not 12. 12:20 AM is 0020. Drop the colon and the AM or PM, and you have the four digits.

The mistakes worth knowing: “00:00 AM” is a mix of both systems and means nothing, because a 24-hour time already says which half of the day it is. And 0000 is not “12 PM”: 12 PM is noon, 1200.

0000 is said “zero hundred”. The “hundred” stands in for the two zeros; nobody says “thirteen zero zero”. The leading zero is spoken: “zero zero hundred”. “Oh zero hundred” is common in conversation and in films, but “zero” is what radio procedure and most instructors use, because “oh” can be misheard.

Minutes follow the same logic. 0005 is “zero zero zero five” and 0040 is “zero zero forty”. Single-digit minutes get a spoken zero, so the listener knows a digit is there.

About the word “hours”: in speech, “zero hundred hours” is everywhere, and nobody will correct you. In writing, Army Regulation 25-50 says the word is not used with military time, so a memorandum reads “at 0000”, not “at 0000 hours”.

On its own, 0000 is local time wherever it is written. When the four digits carry a letter, the letter is the time zone. Z stands for Zulu, which is UTC, and J (Juliet) means the local time of the person speaking. The table converts 0000Z to the four US zones, in standard time and in daylight saving time.

Eastern Time is four hours behind UTC from March to November and five hours behind the rest of the year, which is why one Zulu time maps to two possible local times. The other three zones follow the same pattern an hour further west each.

Midnight has a second spelling, 2400, used when it marks the end of a day rather than the start. The full rules, with a converter, are on the military time chart page.