1000 Military Time

1000 is 10:00 AM, ten o’clock in the morning. On a 24-hour clock with a colon it is 10:00; in military style the colon goes and the four digits stand alone. The hour is 10 hours after midnight and 14 hours before the next one.

Ten in the morning, the first hour written without a leading zero. From here the pattern is simply the number plus “hundred”: ten hundred, eleven hundred, twelve hundred.

To read it, look at the first two digits: the hour is below 12, so add AM: 10 o’clock in the morning. The last two digits are minutes and never change, so 1025 is 10:25 AM and 1050 is 10:50 AM.

Military to 12-hour. Split the four digits into hours and minutes, the hour is below 12, so add AM: 10 o’clock in the morning. So 1015 becomes 10:15 AM and 1045 becomes 10:45 AM.

12-hour to military. 10 AM keeps its number; it already has two digits, so nothing is added: 10:05 AM is 1005. Drop the colon and the AM or PM, and you have the four digits.

The mistakes worth knowing: “10:00 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 1000 is not 10 PM; 10 PM is 2200.

1000 is said “ten hundred”. The “hundred” stands in for the two zeros; nobody says “thirteen zero zero”. Numbers from ten upward are said as ordinary numbers: “ten hundred”, not “one zero hundred”.

Minutes follow the same logic. 1005 is “ten zero five” and 1040 is “ten forty”. Single-digit minutes get a spoken zero, so the listener knows a digit is there.

About the word “hours”: in speech, “ten 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 1000”, not “at 1000 hours”.

On its own, 1000 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 1000Z 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.