Reading and writing military time without the guesswork

Military time is the 24-hour clock written without punctuation and spoken in a particular way. The written form is four digits, no colon: 0930, 1415, 2200. The point of it is that there is exactly one reading of every value, which matters when an order is passed by radio to someone who cannot ask for clarification.

Converting from a 12-hour clock

• Morning hours keep their number and gain a leading zero: 7:05 am becomes 0705.
• Afternoon and evening hours add twelve: 1:00 pm becomes 1300, 7:45 pm becomes 1945.
• Noon is 1200, unchanged.
• Midnight is the one to be careful with. The start of the day is 0000. The end of a day is often written 2359 to avoid any doubt about which date is meant.

Going the other way, subtract twelve from any hour above 12 and add pm, and treat 00 as 12 am.

How it is spoken

The spoken form is where civilians give themselves away. 1300 is "thirteen hundred", not "thirteen o'clock". 0700 is "zero seven hundred", and the leading zero is pronounced. Minutes are read as digits: 1415 is "fourteen fifteen". In some services the hours are followed by "hours" and in others they are not, which is a matter of local practice rather than a rule.

Why midnight deserves its own paragraph

A time written as 2400 is understood by some as the very end of a day and by others as invalid. The safe convention, and the one used in most operational writing, is to avoid 2400 entirely: use 0000 for the start of a day and 2359 for the last minute of the previous one. If a schedule says "0000 on the 5th", the ambiguity is not in the time but in whether the writer meant the moment the 5th begins or the moment it ends, and that is worth clarifying rather than assuming.

The same format, different names

Outside the United States most countries write civil time this way as a matter of course, with a colon: 14:15 on a train timetable, a bank statement or a hospital chart. Calling it military time is a largely American usage, because there the 12-hour clock is the civil default and the 24-hour clock is associated with the services. The digits mean the same thing either way.

For a quick check in either direction, the military time converter takes a 12-hour or 24-hour input and shows both readings, including the awkward hours around midnight where most mistakes happen.