Military time converter

6:00 PM. Subtract twelve from any time of 1300 or later and you have the twelve-hour equivalent: 1800 minus twelve is 6, so 6:00 PM. Times before 1300 keep their hour, so 0900 is simply 9:00 AM.

For 0100 to 1259, read the hour as it stands and add AM. For 1300 to 2359, subtract twelve and add PM. Two times sit outside the pattern: 0000 is 12:00 AM and 1200 is 12:00 PM.

Both are written, and that is exactly why the format needs a rule. 0000 is the start of a day and 2400 is the end of the previous one; the same instant, labelled differently. On a timesheet the start of a shift is 0000 and the end of one is 2400, which keeps a night shift on the right date.

Strictly, no: it is written as four digits and spoken as two pairs, so 1830 is read as eighteen thirty. The 24-hour clock used outside the United States writes 18:30 with the colon. The converter accepts either.

Because AM and PM are easy to mistype and the mistake is expensive. An entry of 7:00 with the wrong half of the day moves twelve hours, and on a night shift it also moves the date. Four digits with no AM or PM cannot be misread that way.

0000. Midnight is the confusing one because twelve reads like the middle of the clock rather than the start of the day. Noon, which people expect to be 0000, is 1200.