How to read, convert and count military (24-hour) time
HESI A2 topic: Military time
- Military time uses four digits, 0000 to 2359, with no a.m. or p.m.
- For 1 to 11 p.m., add 12 to the hour.
- Morning hours get a leading zero: 6:30 a.m. = 0630.
- 12:30 a.m. is 0030; 12:30 p.m. stays 1230.
- Across midnight, count to 2400, then add the time after 0000.
Key facts
- Military time uses four digits, two for the hour (00 to 23) and two for the minutes, with no colon and no a.m. or p.m.; the day runs from 0000 to 2359.
- Morning hours 1 to 11: drop the colon and add a leading zero if needed (9:05 a.m. = 0905).
- Afternoon and evening hours 1 to 11 p.m.: add 12 to the hour (4:20 p.m. = 1620); to go back, subtract 12 from hours 13 to 23.
Show all 7 key factsShow fewer
- The 12 o'clock hours are the exceptions: 12:30 a.m. = 0030 and 12:30 p.m. = 1230.
- Midnight at the start of a day is 0000; NIST notes that 2400 can mark midnight at the end of a day.
- Health care uses 24-hour time on medication records to avoid a.m./p.m. mix-ups: 7 a.m. and 7 p.m. become 0700 and 1900.
- Elapsed time across midnight: count the time up to 2400, then add the time after 0000.
Quick check1 question · 2 more at the end
A clinic schedule lists an appointment at 2015. What is this time on a 12-hour clock?
Correct answer: D.
In military time, hours 13 to 23 are afternoon and evening hours. Subtract 12 from the hour and write p.m.: 20 − 12 = 8, so 2015 is 8:15 p.m. The last two digits (15) are the minutes and do not change.
A This subtracts 10 instead of 12 from the hour (20 − 10 = 10).
B This reads only the first digit, 2, as the hour; the hour is the first two digits, 20.
C This subtracts 12 correctly but labels the time a.m.; any hour from 13 to 23 is after noon, so it must be p.m.
D Correct: 20 − 12 = 8, and hours 13 to 23 are p.m., so 2015 is 8:15 p.m.
Full lesson
Each part starts with its main idea. Open a part when you want the details.
The short answer: Military time counts hours from 00 to 23 and writes four digits with no colon and no a.m. or p.m. For 1:00 to 11:59 p.m., add 12 to the hour (7:15 p.m. = 1915); for morning hours, add a leading zero (6:30 a.m. = 0630). Midnight starting a day is 0000, and noon is 1200.
1 What is military time?Military time is the 24-hour clock. 1 min
Military time is the 24-hour clock. It numbers the hours from 00 to 23, so every time of day has its own number and needs no a.m. or p.m. Elsevier's HESI A2 review book covers regular time versus military time, and health-care records use the 24-hour clock because it removes the a.m./p.m. mix-up.
Each time is written as four digits, two for the hour and two for the minutes, with no colon. The day starts at 0000 and its last minute is 2359. On a medication record, a 7 a.m. and 7 p.m. schedule shows up as 0700 and 1900.
2 How do I convert 12-hour time to military time?Most conversions take one step, and the only tricky ones are the 12 o'clock hours. 1 min
Most conversions take one step, and the only tricky ones are the 12 o'clock hours. Use this table.
| 12-hour time | Rule | Example |
|---|---|---|
| 1:00 to 11:59 a.m. | Drop the colon, add a leading zero if needed | 6:30 a.m. = 0630 |
| 12:00 to 12:59 a.m. | Hour becomes 00 | 12:15 a.m. = 0015 |
| 12:00 to 12:59 p.m. | Hour stays 12 | 12:15 p.m. = 1215 |
| 1:00 to 11:59 p.m. | Add 12 to the hour | 7:15 p.m. = 1915 |
Classic wrong turn: adding 12 to 12:15 p.m. and getting 2415. Noon is already 1200, so the 12 o'clock p.m. hour never changes.
To check your practice answers, use the free military time converter. It also has a full 24-hour chart.
3 How do I convert military time back?m. 1 min
Going back is the same table read in reverse, so for hours 13 to 23 you subtract 12 and write p.m. For example, 2140 becomes 21 − 12 = 9, so 9:40 p.m.
Hours 01 to 11 are a.m. (0845 = 8:45 a.m.), hour 12 is p.m. (1205 = 12:05 p.m.), and hour 00 is the 12 a.m. hour (0020 = 12:20 a.m.).
4 What about midnight, 0000 or 2400?Midnight is the one time that can be written two ways, and the 24-hour clock makes the meaning clear. 1 min
Midnight is the one time that can be written two ways, and the 24-hour clock makes the meaning clear. NIST explains that "12 a.m." and "12 p.m." are ambiguous and recommends against them.
On the 24-hour clock, 0000 is midnight at the start of a day and 2400 is midnight at the end of a day. Nursing conversion charts, such as the one in Open RN, list midnight as 0000. If a question uses 2400, read it as the end of that day.
5 How do I find elapsed time, even across midnight?Subtract the start from the end, but remember that an hour has 60 minutes, not 100. 1 min
Subtract the start from the end, but remember that an hour has 60 minutes, not 100. When the minutes do not subtract, borrow 1 hour as 60 minutes.
Worked example 1. How long is it from 0845 to 1420?
- Minutes: 20 − 45 does not work, so borrow: 1420 becomes 13 hours 80 minutes.
- Subtract: 13 h 80 min − 8 h 45 min = 5 h 35 min.
Worked example 2. A night shift runs from 2130 to 0615 the next morning. How long is it?
- Up to midnight: 2130 to 2400 is 2 h 30 min.
- After midnight: 0000 to 0615 is 6 h 15 min.
- Add: 8 h 45 min.
Classic wrong turn: subtracting straight across (2130 − 0615) gives 15 h 15 min, the time between the two clock readings within a single day, not the shift.
Common mistakes
The traps students fall into most. Read these before you practice.
Watch out: Do not add 12 to a 12:xx p.m. time: 12:45 p.m. is 1245, not 2445.
Watch out: A 12:xx a.m. time starts with 00, not 12: 12:10 a.m. is 0010.
Watch out: Minutes run to 60, not 100: from 0950 to 1010 is 20 minutes, not 60.
Watch out: 1800 is 6:00 p.m., not 8:00 p.m.; subtract 12, not 10.
Watch out: If the end time is smaller than the start time, the period crossed midnight; add 24 hours to the end time before subtracting.
How to remember it
Think of the clock as a ruler that keeps counting past noon instead of starting over at 1.
Memory hook: "After noon, plus twelve; at midnight, zero."
Self-check:
- Write 11:50 p.m. and 12:05 a.m. in military time.
- What 12-hour time is 1745?
- How long is it from 2250 to 0110?
Show answers
- 2350 and 0005.
- 11:50 p.m. is a p.m. hour from 1 to 11, so add 12: 11 + 12 = 23, which gives 2350.
- 12:05 a.m. is in the 12 a.m. hour, so the hour becomes 00: 0005.
- 5:45 p.m.
- The hour 17 is between 13 and 23, so subtract 12: 17 − 12 = 5.
- Keep the minutes and write p.m.: 5:45 p.m.
- 2 h 20 min.
- The end time is smaller than the start time, so the period crossed midnight.
- Up to midnight: 2250 to 2400 is 1 h 10 min.
- After midnight: 0000 to 0110 is 1 h 10 min.
- Add: 1 h 10 min + 1 h 10 min = 2 h 20 min.