Is 12 AM Midnight or Noon? 12 AM vs 12 PM Explained
The short answer, the reason it confuses people, and how to write noon and midnight so nobody gets the day wrong.
Updated
Short answer
12 AM is midnight and 12 PM is noon. That's the generally accepted convention, though there's no official standard, and the US National Institute of Standards and Technology calls both labels ambiguous.
12:00 AM = midnight, the start of the day = 00:00 or 0000 in 24-hour and military time.
12:00 PM = noon, the middle of the day = 12:00 or 1200.
The short answer is easy, but the labels still cause missed deadlines and wrong-night reservations, so here's why they're confusing and how to write times nobody can misread.
Why 12 AM and 12 PM are confusing
AM and PM come from Latin. AM stands for ante meridiem, "before midday", and PM for post meridiem, "after midday", according to Royal Museums Greenwich. Noon is midday itself, so strictly speaking it's neither before nor after midday. Midnight is the same problem twelve hours away. Royal Museums Greenwich points out that noon and midnight are technically neither AM nor PM.
The everyday convention fills that gap. The UK's National Physical Laboratory (NPL) says there is no official standard, but "it is generally accepted that 12am means midnight and 12pm means midday."
The reason it feels backwards is how the hours run. The AM label starts at midnight and covers the morning: 12:00 AM, 12:01 AM, through 11:59 AM. At noon the label flips to PM and the count starts again from 12. So 12 PM comes right after 11:59 AM, even though 12 looks like it should come first.
Is 12 AM Friday Thursday night?
This is the question that causes real problems. Midnight belongs to the day that's starting. NPL notes that the moment the clock hits midnight marks the start of a new day, so 12:00 AM Friday is the very start of Friday, the moment Thursday night ends.
That means:
- A deadline of "12 AM Friday" falls at the end of Thursday, not the end of Friday. It's easy to read it as Friday night and miss it by a full day.
- An event at "12 AM on the 15th" happens when the 14th turns into the 15th.
When the exact day matters, check with whoever set the time. Not everyone uses the convention correctly.
Does 12 AM to 12 AM mean all day?
Usually, yes. "12 AM to 12 AM" normally means a full 24 hours, from the start of one day to the start of the next. "Monday 12 AM to Tuesday 12 AM" covers all of Monday. Because the same label shows up at both ends, it's easy to misread, so written schedules often use the forms below instead.
How to write noon and midnight so nobody misreads them
- Use the words. NPL recommends saying midday, noon, and midnight rather than 12 AM or 12 PM. "12 noon" and "12 midnight" are also clear, and Royal Museums Greenwich suggests them too.
- Use 11:59 PM or 12:01 AM for deadlines. NPL notes that transport timetables use 23:59 or 00:01 to make it clear which day they mean. "Due 11:59 PM Thursday" can't be misread.
- Use the 24-hour clock. Noon is 12:00 and midnight is 00:00, with no AM or PM to get wrong. The military time converter switches any time between the two formats.
- Add the day. "Midnight at the end of Thursday" or "the start of Friday" removes all doubt.
Quick reference
| 12-hour | What it means | 24-hour | Military |
|---|---|---|---|
| 11:59 PM | One minute before midnight | 23:59 | 2359 |
| 12:00 AM | Midnight, start of the new day | 00:00 | 0000 |
| 12:01 AM | One minute after midnight | 00:01 | 0001 |
| 11:59 AM | One minute before noon | 11:59 | 1159 |
| 12:00 PM | Noon | 12:00 | 1200 |
| 12:01 PM | One minute after noon | 12:01 | 1201 |
Key points
- 12 AM is midnight and 12 PM is noon in everyday use.
- Midnight starts the new day, so 12 AM Friday is the end of Thursday night.
- For deadlines, write 11:59 PM, the words noon or midnight, or 24-hour time.
Need to know what time it was or will be a few hours from now, across midnight? The hours ago calculator works it out from your own clock and shows the day.
Sources
This guide was written by Cedrick Reese for Timer Calculator. The conventions come from the UK National Physical Laboratory, Royal Museums Greenwich, and NIST, linked under Sources, and were checked against all three. For the quick-reference table, each of the six 12-hour times was typed into the military time converter in an automated browser test, and its 24-hour and military results match the table.