Noon and Midnight: 12 PM or 12 AM?

Summary

Simply use the words noon and midnight instead of 12 a.m. or 12 p.m.

Example
  • Incorrect: The conference begins at 12 p.m. on Monday.
    Correct: The conference begins at noon on Monday.

Using the number 12 with noon and midnight is redundant.

Example
  • Poor: The bell rang at 12 midnight.
    Better: The bell rang at midnight.

On the 24-hour clock, both 00:00 and 24:00 are midnight, indicating the start and end of a day. Prefer to show time frames using 00:01 and 23:59 to avoid confusion about which day is being referred to. Noon is 12:00 on the 24-hour clock.

Examples
  • Correct: Free time is deemed to commence at 00:01 of the first day.
  • Correct: The portal will remain open from 12:00 to 23:59 on March 3, 2053.

Both noon and midnight are referred to as 12 o’clock (or simply 12 or twelve) informally.

Example
  • Informal: The show starts at 12 o’clock.
    Context makes it clear whether it is noon or midnight.

Noon and midnight

Midnight is when the 24-hour period of a day ends and a new day begins. Noon or midday is the middle of the 24-hour period: the point at which 12 hours have passed.

Examples
  • Rita went to bed at midnight and woke up at ten this morning.
  • We break for lunch at noon.

Time references to noon and midnight can be confusing for readers and writers alike. In this article, we discuss rules and style guidelines around references to noon and midnight in writing.

12 a.m. and 12 p.m.

Simply use the words noon and midnight instead of 12 p.m. or 12 a.m.A.m.” means ante meridiem or “before midday” (to refer to times before noon), and “p.m.” stands for post meridiem or “after midday” (to refer to times after noon). At noon, therefore, it is neither a.m. nor p.m., and for this reason, referring to midnight as a.m. or p.m. does not make sense either.

Examples
  • Incorrect: The portal closes at 12 p.m.
    Not only is it technically incorrect to refer to noon as “p.m.,” it is also confusing: readers may be left wondering whether you mean noon or midnight.
    Correct: The portal closes at noon.
  • Incorrect: Your train leaves at 12 a.m.
    Correct: Your train leaves at midnight.
  • Incorrect: The deadline for submissions is 12 p.m. on Monday.
    Correct: The deadline for submissions is noon on Monday.
Note

When people do use a.m. and p.m. to refer to noon and midnight, they generally use “12 p.m.” for noon and “12 a.m.” for midnight. Since this is both confusing and illogical, avoid such usage altogether, and prefer to simply use the words noon and midnight.

Using the number 12 with the words noon and midnight is redundant, since noon and midnight cannot be anything but 12 on the clock.

Examples
  • Poor: The fun began at 12 midnight.
    Better: The fun began at midnight.
  • Poor: At 12 noon, a ship appeared on the horizon.
    Better: At noon, a ship appeared on the horizon.

24-hour system: 00:00 and 24:00

On the 24-hour clock, both 00:00 and 24:00 indicate midnight. When to use which depends on context: 00:00 indicates the start of a day, while 24:00 refers to the end of a given day.

Examples
  • From 00:00 to 01:00, the Moon was eclipsed by the Earth.
    midnight at the start of a day
  • The broadcast began at 2330 and ended at 2400 hours.
    midnight at the end of the same day the broadcast began

Some house styles recommend using 00:01 and 23:59 to indicate the start and end of a day to avoid confusion.

Examples
  • The portal to Andromeda will open at 00:01 on May 23, 2093.
  • Please submit your applications by 23:59 to avoid automatic rejection.

Noon is 12:00 or 1200 hours on the 24-hour clock.

Examples
  • Your flight departs at 12:00 tomorrow.
  • The captain sounded general quarters at 1200 hours.
Tip

The word hours in the 24-hour system is optional. When a colon is used as a separator between hour and minute, hours is generally omitted.

Example
  • Your flight is at 2030 hours.
    or
    Your flight is at 20:30.

12 o’clock

In informal usage, both noon and midnight are referred to as 12 o’clock (or simply 12 or twelve), with context making it clear whether it is day or night.

Examples
  • Let’s have brunch at 12 o’clock this Sunday.
    A clear reference to noon, since brunch isn’t generally had at midnight.
  • On weekdays, Tumkin goes to bed at 12 o’clock and wakes up at six in the morning.
    A clear reference to midnight, since people usually go to bed at night.
  • Let’s meet at twelve at the café.
  • The Harrises have asked us to be there by 12.

In formal writing, prefer to use the words noon and midnight or the abbreviations a.m. and p.m. instead of the term o’clock.

Examples
  • We worked steadily from 8 a.m. to noon and then broke for lunch.
  • The deadline to submit your report is Friday midnight.

Usage guide

Use the words noon and midnight instead of 12 a.m. or 12 p.m. Using the numeral 12 with noon or midnight is unnecessary, and such usage is generally avoided in edited prose, since it is always 12 at noon and midnight. On the 24-hour clock, noon is 12:00 (or 1200 hours). Midnight is 00:00 at start of day and 24:00 at end of day. If confusion is possible, prefer to use 00:01 and 23:59 instead to mark start and end of day. Finally, 12 o’clock (or simply 12 or twelve) may refer to either noon or midnight in informal usage.

Quick Quiz

Which is noon?
Choose from these answers
All done!
Which is better style?
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All done!
Which is midnight in the 24-hour system?
Choose from these answers
All done!
Which is preferred in formal writing?
Choose from these answers
All done!

Did You Know?

It’s fine to use because at the start of a sentence.
Know more:Can “Because” Start a Sentence?