From what I understand, the word "midnight" is usually interpreted incorrectly.

Midnight is written as "12am" which would imply that it's in the morning. Therefore, it should be at the start of the day. On the other hand, both Dictionary.com and the Oxford Dictionary define it as "twelve o'clock at night".

Some examples:

  1. "Midnight on the 10th of December"
  2. "Midnight Thursday"
  3. "Midnight tonight"

are usually interpreted as:

  1. Straddling the 10th and the 11th of December
  2. Straddling Thursday and Friday
  3. Straddling today and tomorrow

but should they technically mean:

  1. straddling the 9th and the 10th of December?
  2. straddling Wednesday and Thursday?
  3. This is much less clear. Technically is there a midnight "tonight", or is midnight "tomorrow morning"?

What do you think? How should "midnight" be interpreted?

  • 1
    That's why deadlines are usually 11:59 pm – Unrelated Jul 22 '16 at 21:18

It's a matter of convention, and the informal convention is that "midnight on the 10th" is more commonly the night between the 10th and the 11th. But the term is awfully ambiguous, and people do use it both ways.

(When I've scheduled things with "midnight" deadlines, I always say "11:59pm on the 10th" or something like that, to avoid the ambiguity. From experience, if you don't people will ask which you mean.)

  • 7
    As a programmer, I deliberately avoid the ambiguity as well. "By the end of the 10th", or "Before the 11th" generally work as well. – Damovisa Dec 9 '10 at 5:42
  • Thank you so much @Damovisa. I'm actually sitting right now trying to fix ambiguous period description in the app that I'm working on and "By the end of the 10th" is a perfect way to be unambiguous. – Rafał Cieślak Mar 9 '19 at 15:05

By most definitions, the date changes at midnight. That is, at the precise stroke of 12:00:00. That time, along with 12:00:00 noon, are technically neither AM or PM because AM and PM mean "ante-meridiem" and "post-meridiem", and noon and midnight are neither ante- nor post- meridiem. However, for convenience, most people lump the 12:00:00 time with its nearest neighbour, 12:00:01, which IS AM or PM.

Since the date changes at the stroke of midnight, there is always ambiguity about which date you refer to. Midnight on the 10th technically means at the start of the 10th, but when most people speak they mean it to be at the end of the 10th.

If I said "I'll meet you Friday at midnight" or "I'll meet you Friday night at midnight" you (and most people) would probably interpret both times as the midnight that follows Friday noon. However, there are cases where the first sentence really means "the midnight at the start of Friday".

Since the common usage conflicts with the technical definition, if you want to be totally clear, use other words or other times.

Friday night at midnight

probably will always be interpreted as "Midnight in the night which follows Friday evening".

Midnight tonight

This means (to me) the midnight following today.

11:59 PM Friday

12:01 AM Saturday

These are totally unambiguous.

  • I think this summarises what I'm getting out of these answers. Technically, "midnight" doesn't belong to either day, but conventionally it's usually understood at the end of a day not the beginning. – Damovisa Dec 9 '10 at 22:32
  • Note that leap seconds, when they occur, typically are inserted at 23:59:60 UTC. Eg, there was one a month ago, at 30 June 2012, 23:59:60 UTC. At that midnight, 23:59:59 and 00:00:00 were 2 seconds apart instead of 1. – James Waldby - jwpat7 Jul 27 '12 at 19:10
  • @jwpat7 Note that leap seconds occur simultaneous thought out the world. With local time, that extra second may be in the morning or afternoon, not near local midnight - unless your timezone matches UTC. – chux - Reinstate Monica Jun 9 '15 at 20:32
  • @chux, yes, of course; that's the usual nature of UTC times. – James Waldby - jwpat7 Jun 11 '15 at 3:59

The convention stems from the term itself. Midnight comes from 'mid-night.'

In conversation, the 'night' of which 'midnight' is in the middle, is considered the night of the date mentioned.

If you are referring to a deadline, this also will refer to the stroke of 12 after the evening of the same date.


The paper is due by Friday at midnight.

Should not be confusing to anyone. Plus, since the only confusion could possibly be that it was due a day earlier, there can be no misunderstanding excuse for not getting the paper in on time. ;-)

The entire convention is based on the typical human schedule of being awake during the day and asleep during the night. Even the 'wee hours' can be used conversationally to mean the 'night' prior.


We stayed out Friday night until 3am!
We were out until 3am Saturday morning!

  • 2
    This is a good answer, but experience shows that you're wrong -- it can be confusing, and to many people. Stamping your feet about how illogical and unthinking humans are doesn't change that fact... – Jonah Sep 24 '16 at 17:50

Another way to avoid ambiguity is to use a 24 hour clock. Midnight between Thursday and Friday is 2400 Thursday, and 0000 Friday.


If we apply your argument to 12pm, being labeled in that fashion implies that it is in the evening, and therefore it must be at the end of the day. Thus, people are wrong to go around calling it "noon", which is clearly in the middle of the day, not the end. :-)

By convention, "midnight on the 10th of December" should refer to the end of the day of December 10, the instant before December 11 starts. If I say "last midnight" you can be assured that I am referring to a time less than 24 hours ago, and if I say "midnight tonight" I am referring to a time less than 24 hours in the future.

  • Ooh, very good point RE noon :) I think the learning here is that it's convention that really defines the meaning. – Damovisa Dec 9 '10 at 5:31
  • If you want to be pedantic, 12:00:00pm is not a valid time. The PM part means "post meridian" which 12:00:00 is not. It is merely convention that 12:00:00 (which follows 11:59:59am and is followed by 12:00:01pm) is labelled 12:00:00pm. The point remains that midnight touches two dates and is technically part of the start of the day not the end. Your examples of "last midnight" and "midnight tonight" provide enough additional context to remove any ambiguity about which midnight the speaker means. – Mr. Shiny and New 安宇 Dec 9 '10 at 15:22
  • Whoops, RegDwight corrected me on my answer, but I didn't notice I made the same mistake here. PM means Post Meridiem not Meridian. – Mr. Shiny and New 安宇 Dec 10 '10 at 14:23

If you look at most writing and scientific guides, there is no such thing as 12 a.m. or 12 p.m. Technically, you should refer to 12 noon or 12 midnight. It's technically neither. It's just midnight. The abbreviations for am and pm come from the Latin words "ante meridies" (am) and "post meridies" (pm). Meridies means noon, so post meridies means after noon and ante meridies means before noon. Since the date changes at the stroke of midnight, there is always ambiguity about which date you refer to. Midnight on the 10th technically means at the start of the 10th, but when most people speak they mean it to be at the end of the 10th. In 24-hour time notation, "00:00" and "00:00:00" refer to midnight at the start of a given date.

See also: Is Midnight Am PM?


The existing answers are already good, but for anyone who might get confused, I think this might be an easy way to remember the common definition: "Friday midnight" means "middle of Friday night".

Since Friday night pretty much never refers to early morning Friday, it stands to reason that neither does the middle of Friday night.

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