How to Tell Military Time — Basic Training

I never served in the military, so when I started reading and writing progress notes in the hospital I was a little thrown off by the military time used in patient charts. In a world where half the written information already looks like another language writing the time in military fashion seemed like a disaster waiting to happen. Well, at least until I realized how much better military time actually is.

Obviously, I had to learn how to read military time quickly and accurately for patient safety but it is actually quite easy and when you have it down it’s far quicker and leads to far fewer errors than using standard 12-hour time.

There are two main methods for telling time: 12-hour and 24-hour. In the U.S., us civilian folk typically stick to the 12-hour clock. The 12-hour clock is divided into two periods: ante meridiem (a.m.) are the 12 hours from midnight to noon and post meridiem (p.m.) are the 12 hours from noon to midnight. The 24-hour clock system is not divided, a day is a continuos run of 0-23 hours from midnight to midnight. Today ends at 2359, tomorrow begins at 0000. Sometimes to indicate the end of a day you might see 2400 (ie. Tuesday at 2400 is Tuesday at midnight and Wednesday begins at 0000).

When you depend on strict accuracy in timing the 12-hour clock starts to display obvious disadvantages. For example, I write an order for a patient to receive a drug at 08:00. Is that 8am or 8pm? And thus a potentially life threatening mistake is born. Obviously, I would be sure to write 08:00am or 08:00pm when writing an order if I used the 12-hour clock but even that can go wrong. A single letter indicates a 12-hour time difference so a small typing error which doesn’t look immediately obvious or a reading error can cause big problems. If I tell you 12-O’clock is that noon or midnight?

The 12-hour clock also makes calculating time additions or subtractions very difficult. If it’s 8:00am and you’re going to be working for 10 hours when do you get off? Well its 4 hours to noon, 10 minus 4 is 06:00pm. Or maybe you do 08:00am plus 10 hours is 18:00 minus 12 is 06:00pm. Regardless, see any room for potential adding / subtracting errors there?

The 24-hour clock clears up our big issues. There is no question that 0000 is the beginning of the day as there is no question that 2359 or 2400 is the end. It may take a few days to get used to thinking of 2200 as the equivalent of 10:00pm but there is no questioning the fact that you can’t confuse 2200 as 10:00am. Calculating is also much easier. Again, if you start work at 0800 and work for 10 hours when do you get off? 1800 hours. Simple.

It’s no wonder countries picked up military time. The earliest to do so was Italy, in 1893. In 1920, the US Navy was the first US organization to adopt the system; the US army, however, did not officially adopt the 24-hour clock until World War II, on July 1, 1942.

Converting military time to civilian time is a cinch once you get used to it.

• From 1am to 9am you use the same numbers and simply add a 0 before it.  8:00am becomes 0800
• If military time is 1300 or higher you just subtract 1200.  1645 becomes 04:45pm

When writing military time you just write down the numbers, no colon, no am / pm. When speaking military time you say the numbers.

• 0800 : ‘zero eight hundred’
• 0415  : ‘zero four fifteen’
• 1650  : ‘sixteen fifty’