Military Time on Time Cards: 12 AM, 12 PM and 2400

How to convert, in two rules

1. From 1:00 AM to 12:59 PM, keep the hour. 7:58 AM is 0758. 11:15 AM is 1115. Noon is 1200, and 12:30 PM is 1230.
2. From 1:00 PM to 11:59 PM, add 12 to the hour. 1:00 PM is 1300. 4:34 PM is 1634. 7:15 PM is 1915. 11:59 PM is 2359.

The one exception is the midnight hour. 12:00 AM is 0000, and 12:30 AM is 0030. To go back from 24-hour time, subtract 12 from any hour 13 or higher and add PM; for 00, write 12 and add AM.

On cards and screens you may see the same time as 1634 or 16:34. They mean the same thing.

The full 24-hour chart

Minutes never change. Only the hour does: 1847 is 6:47 PM, and 0803 is 8:03 AM.

12 AM, 12 PM, noon and midnight

The National Institute of Standards and Technology (NIST) puts it plainly: “12 a.m. and 12 p.m. are ambiguous and should not be used.” Noon is neither before nor after noon, and midnight is both. NIST adds that a digital clock should switch to PM the moment it reaches 12:00 noon, which is why 12:00 PM usually means noon and 12:00 AM means midnight. People still mix them up often enough that a 24-hour card is the safer record.

Here is what the mix-up does to a time card:

• A shift from 7:00 PM to midnight is 5:00. Write the end as 12:00 PM by mistake and the arithmetic reads 7:00 PM to noon the next day: 17:00.
• A shift from 12:00 AM to 8:30 AM is 8:30. Write the start as 12:00 PM and the shift turns into an overnight one of 20:30.

On a 24-hour card the same shifts are 1900–0000 and 0000–0830, and there is nothing to mix up. If your card uses 12-hour times, writing noon or midnight in words is clearer than 12 PM or 12 AM.

0000 or 2400: which day does midnight belong to?

Midnight is the end of one day and the start of the next. The 24-hour clock has a way to say which one you mean. NIST notes that 0000 can mark midnight at the beginning of a date and 2400 midnight at the end of a date. So 2400 on Friday and 0000 on Saturday are the same moment.

For a time card, that means:

• A shift ending exactly at midnight can be written 1600–2400 on the day it started. That is 8:00, and it stays on one line.
• The same shift written 1600–0000 is also 8:00. The out time looks smaller than the in time, which simply means the shift ran to the next day.
• Never write 2400 as a start time. A shift that starts at midnight starts at 0000 on the new date.

Which day the minutes belong to matters for overtime. Under the federal rule, a workweek is a fixed period of 168 hours that can start on any day and at any hour (29 CFR 778.105), and federal recordkeeping rules define a workday as a fixed period of 24 consecutive hours (29 CFR 516.2). If your workweek starts at midnight, a shift running past 2400 on the last day puts its later minutes in the next week.

Adding up a 24-hour time card

Subtract the in time from the out time, borrowing 60 minutes when the out minutes are smaller. No AM/PM step is needed.

A day shift. In 0758, out 1634. The minutes 34 are fewer than 58, so borrow an hour: 1634 becomes 15 hours and 94 minutes. 94 − 58 is 36 minutes and 15 − 7 is 8 hours: the span is 8:36. With a 30-minute meal break, the day is 8:06 (8.10 hours).

A night shift. In 2200, out 0630. The out time is smaller, so the shift crossed midnight: 2200 to 2400 is 2:00, and 0000 to 0630 is 6:30. The span is 8:30, and with a 30-minute break the shift is 8:00 (8.00 hours).

A whole week. Here is a week as a 24-hour time clock would print it, with the unpaid meal break for each day:

The total is the same as in 12-hour notation, because only the labels changed. The guide on how to calculate hours worked walks through this week step by step.

Mistakes to watch for

• Reading 1630 as a decimal. 1630 is 4:30 PM, a clock time. A shift of 16:30 hours is 16.50 decimal hours, not 16.30. See minutes to decimal hours for the chart.
• Dropping the leading zero and losing the morning. 0830 is 8:30 AM. If a handwritten 830 is later read as 2030, the day grows by 12 hours. Write four digits.
• Subtracting as if the minutes were hundreds. 1634 − 0758 typed into a plain calculator gives a number that is not a time at all. Clock minutes run to 60, so subtract hours and minutes separately.
• Midnight on the wrong date. A shift that ends at 2400 on Friday and one that starts at 0000 on Saturday touch the same moment. Put each on its own date.
• Daylight saving nights. On the night the clocks change, a 2200–0630 shift is not 8:30 of clock time. See the guide on daylight saving time and night shifts.

Federal rules do not require any particular format for time records. Fact Sheet #21 says employers may use any timekeeping method, as long as it is complete and accurate, so a 12-hour card, a 24-hour card or a clock printout can all be valid records. What has to be right is the hours.

Next step

Convert any time either way, or print the full chart, with the military time converter.