# Why does 12 am come first?

The 12-hour clock can be confusing at times, especially when trying to distinguish between 12am and 12pm. Though it may seem counterintuitive, there is a logical reasoning for why 12am comes before 12pm.

## Defining 12am and 12pm

First, let’s clarify the meaning of 12am and 12pm:

• 12am – This refers to midnight, or the very start of a new day. For example, 12am on Monday is the beginning of Monday.
• 12pm – This refers to noon, or the middle of the day. For example, 12pm on Monday is midday on Monday.

So in summary:

Time Meaning
12am Start of day (midnight)
12pm Middle of day (noon)

## The 24-hour clock

To understand why 12am precedes 12pm, it helps to think about the 24-hour clock:

• In the 24-hour clock, the day starts at 00:00 (spoken as zero hours, zero minutes). This is midnight.
• 12:00 in the 24-hour clock is spoken as twelve hundred hours. This is noon.

So on the 24-hour clock, midnight (00:00) comes before noon (12:00).

When we convert the 24-hour clock to the 12-hour clock, 00:00 becomes 12am, and 12:00 becomes 12pm.

Therefore, based on the 24-hour timeline, 12am (midnight) comes before 12pm (noon).

## Why midnight is the start of the day

Now this raises another question – why does a new day start at midnight on the 24-hour clock? Here are some reasons:

• Historically, the Egyptians divided the day into two 12-hour periods. The first period began at sunrise and the second at sunset. During the night, they measured time by the rising and setting of stars, so midnight was seen as the start of a new cycle.
• Midnight is the middle point between sunset and sunrise. So it’s a logical transition point between one day and the next.
• It matches our natural sleep cycle. We tend to be asleep during the night hours and awake during daylight, so midnight signals the start of a new wake/sleep rhythm.

Therefore, midnight serves as a convenient dividing line between distinct 24-hour cycles we call days.

## How the 12-hour clock aligns with the 24-hour clock

Now that we’ve established midnight as the start of the 24-hour clock, let’s look at how the 12-hour clock synchronizes with it:

24-hour clock 12-hour clock
00:00 12:00am
01:00 1:00am
11:00 11:00am
12:00 12:00pm
13:00 1:00pm
23:00 11:00pm

As you can see, 12am (midnight) is aligned with 00:00, while 12pm (noon) falls at 12:00. This mirrors the 24-hour timeline.

## Why mixing up am and pm causes problems

Given that 12am and 12pm are opposite times of day, mixing them up can cause big problems:

• You could show up to an appointment 12 hours early or late.
• You could set your alarm incorrectly and oversleep.
• You could take medicine at the wrong time of day.

So paying attention to the correct label of am or pm is very important in avoiding confusion!

## Tips for keeping am and pm straight

To avoid mixing up 12am and 12pm, here are some helpful tips:

• Say “midnight” and “noon” instead. This makes it clear which is which.
• Remember that am = before noon. pm = after noon.
• Visually picture a day timeline from midnight to noon to midnight.
• Double check by looking at a 24-hour clock.

## Why some countries use a 24-hour clock

To avoid this 12am/12pm confusion, many countries use the 24-hour clock instead of the 12-hour clock. For example:

Country Use of 24-hour clock
China Primary clock system
Spain Primary clock system
Latin America Widely used alongside 12-hour clock
Italy Used in transportation schedules

On the 24-hour clock, there is no chance of mixing up 12am and 12pm, since midnight is 00:00 and noon is 12:00. The time is unambiguous.

## The bottom line

While the logic behind 12am coming before 12pm is not always intuitive, there are straightforward reasons:

• 12am = midnight = start of day in 24-hour timeline
• 12pm = noon = middle of day
• So based on the 24-hour clock, 12am precedes 12pm

Being careful about using the correct am or pm label is key to avoiding potential confusion. And in many countries, the 24-hour clock skips this issue entirely by using unique numbers for all 24 hours.

So while it may not seem logical at first, there are practical reasons why 12am comes before 12pm on the 12-hour clock!