Is midnight part of today or part of the next day?

It is neither. It is not a.m., and it is not p.m. It is Midnight. It is the dividing line between two dates.

(Noon is neither afternoon or morning).

If midnight is a singular moment, possessing no length of time itself, it is neither.
If it has a length, and starts at 00:00, then it is part of the next day.
If it has a length, and is a period of time before and after 00:00, then it is both.

12:00AM is the next day. I agree that it makes no sense and I’ve never understood the logic behind it.

12pm is noon
12am is midnight.
It’s just the convention. It could be the other way round.

It’s actually the start of the new day. Clocks are the same 24 clocks anywhere.

Mid-Noon, Noon-Mid.

In a hospital setting if you are in a bed at 1 minute past midnight, you are charged for the entire day.

Once it’s 12 (am/pm) it is the next day. It’s the beginning of the next day/afternoon

Neither. It is the cusp of the two.

Well…people do wish each other a happy new year or happy birthday at the stroke of midnight. So it makes sense that it’s part of the next day.

But then that means that the phrase “Let’s meet at midnight tonight!” would never be technically correct.

And my brain is mostly following @zenvelo ‘s train of thought. If AM means “ante meridiem” and PM means “post meridiem”, then the meridian(s) can’t be AM or PM, right?

It’s both the beginning and the end. I think a lot of people think of it as the end, because it’s while they sleep. If I have to choose I call it the beginning since it’s AM.

When I was first learning about time as a little girl, I remembered midnight was AM, because to me noon made sense as PM. It was only for that reason that I knew the other 12:00 (midnight) is AM. PM, post meridian, just sounds to me like the sun would be high in the sky.

On the 24 hour clock it is 00:00 and 24:00. Typically, although not necessarily, you would use 00:00 if it’s a start time, and 24:00 if it’s an end time.

@raum The phrase let’s meet at midnight tonight just designates the time after sunset and before dawn. Neither “11:30 tonight” nor “12:30 tonight” have anything to do with today or tomorrow.

After midnight is technically “tomorrow” but if I said to someone “it’s going to be on TV tomorrow at one o’clock in the morning” then they would probably think of the show being over 24 hours from now, and it would sound that way to me, too.

It is the start of the next day. Two arguments to justify that conclusion.
1. Since 12:01 is in the next day, shouldn’t 12:00 also be?
2. If we changed 12 to 0, it would be obvious that 0:00 is on the next day.

^^It is both 00:00 and 24:00 on the 24 hour clock. On our analog clocks we can only fit one number, and the click makers decided on 12 I guess.

@LostInParadise My job uses military time, clocks day ends at 23:59:59. There is no 24:00:00.

00:00:01 is the first minute of the new day.

The militaries tend to not use 24:00 it’s true. I think some of it is just what is the custom of the group using the 24 hour clock. It’s not just the military, many European countries use 24 hour clocks, possibly other parts of the world too.

Some places discourage 00:00 and 24:00 and encourage 23:59 and 00:01 to indicate starting and finishing the first minute of the day or last minute of the day respectively.

Basically, the :00 is a ten, or hour ending at ten. What I mean is you count, starting at “1” and you end at “10.” So the segment of the day, like morning, would end at 12:00 hours, inclusive, and afternoon would end at 00:00 hours, inclusive. The next segment would begin at 12:01 and 00:01 respectively.

If 00:00:01 is the first second of the new day, then logic would dictate that midnight (zero minutes and zero seconds into the start of the day) should be 00:00:00. What does the clock show for the second before 00:00:01? This link says the military uses both 00:00 and 24:00. 24:00 makes no sense. That 24 hour lasts only until 00:01.

It really does not in any way matter if Midnight is recorded on a clock as 24:00:00 or 00:00:00. It belong to neither day. It is the moment when the clock changes, the moment when the name of the day changes, when tomorrow becomes today.

It is a transition. It is Midnight.

Not that this is authoritative, but I had a Heathkit digital clock back in the 1970s that I put together.

It went from 23:59:59 to 00:00:00. But it only stayed that way for a second :-)

@zenvelo , You are right of course. Midnight marks the simultaneous end of the old day and start of the new day. Still, it makes much more sense to treat 00:00, the start of hour 0, as the start of the new day and make it AM along with the rest of the hour.

The next day.

From a software standpoint, midnight is 00:00:00, the start of the day. Since computers run our lives… :)