Is 12 PM Noon or Midnight?
12 PM is noon and 12 AM is midnight — but the labels are genuinely ambiguous, and style guides tell you to avoid them. Here is why, and what to write instead.
12 PM is noon. 12 AM is midnight. That is the convention, and it is the answer you want if someone just asked.
But the convention is weakly held, widely misread, and several style guides recommend against ever writing it. If the meeting matters, do not write 12 PM.
Why It Is Confusing
AM stands for *ante meridiem*, before midday. PM is *post meridiem*, after midday. Noon is neither — it is the meridiem, the moment the labels are defined relative to. Midnight is equally awkward, sitting exactly 12 hours from it.
So assigning 12:00 to PM is an arbitrary tiebreak, not a logical consequence. Half the people you ask will guess the other way, and they are not being careless.
What the Standards Actually Say
- NIST (US time authority) advises avoiding 12 AM and 12 PM entirely, and writing *noon* or *midnight*.
- The Chicago Manual of Style recommends the same.
- ISO 8601 sidesteps it by using the 24-hour clock, where noon is 12:00 and midnight is 00:00 or 24:00 depending on whether you mean the start or end of the day.
The Midnight Problem Is Worse
Noon is at least unambiguous once you know the rule. Midnight belongs to two dates.
"Midnight on Friday" can mean the instant Friday begins or the instant it ends — a 24-hour difference. Contracts, deadlines and opening hours all get this wrong regularly. See [0000 vs 2400 military time](/blog/0000-vs-2400-military-time) for how the 24-hour clock handles the same problem.
What to Write Instead
| Ambiguous | Clear |
|---|---|
| 12 PM | 12 noon, or 12:00 |
| 12 AM | 12 midnight, or 00:00 |
| Midnight Friday | 23:59 Friday, or 00:00 Saturday |
| Deadline: 12 AM Monday | Deadline: Sunday 23:59 |
For deadlines specifically, 23:59 removes the problem entirely: it is unmistakably the end of that day, and nobody has to decide which side of midnight it falls on.
Is 12 PM Day or Night?
Noon, so daytime. 12 AM is the middle of the night. The full comparison is in [12 AM vs 12 PM](/blog/12-am-vs-12-pm).