Is 12:00AM Midnight or Noon?

The AM PM 12 hour time format can be confusing. When is 12:00AM Tuesday? Is it midnight on Monday, Tuesday noon, or Tuesday midnight? “It’s Tuesday morning!” you may say confidently, but is it?

You would not be the first person to disagree or be confused. We asked 100 people and received three answers to this question. That’s a range of 24 hours. You might be interested to know that there are no established standards for the meaning of 12:00 AM nor 12:00 PM, but there are answers. You may think you know, but you may not be right. Around 50% of the people we asked were wrong. Confused? Alright. Set your clocks, let’s go.

30-second overview:

In this article we explain the 12 hour AM PM clock format and answer questions including:.

Who is Timewatch?
Timewatch are specialists in time – planning it, managing it and tracking it. We develop professional services software including game-changing Outlook and Google timesheet systems Outlook and Google timesheet systems – we know how time works and in this article we answer questions we are often asked asked. 

What does AM and PM stand for?

Let’s start at the beginning. What exactly does ‘AM’ and ‘PM’ mean? One ‘day’ totals 24 hours. Most clocks divide a day into two 12-hour periods of AM and PM

  • AM stands for the Latin “ante meridiem”, which translates to before midday. This is the time before the sun has crossed the meridian.
  • PM stands for “post meridiem” or after midday. This is when the sun has crossed the meridian.

The meridiem is an imaginary semicircle that crosses the sky from due north to due south at your local noon. So AM is the morning, when the sun has not yet reached the meridiem, and PM is the afternoon, after it has passed the meridiem. So, AM is morning, PM is afternoon, and when the sun is exactly on the meridiem this is noon or midday.

This is great for understanding AM and PM meaning but things are about to get complicated. According to the Royal Observatory in Greenwich, London, (this is where Greenwich Mean Time or GMT originates) at exactly 12 noon, the Sun is at its highest point in the sky and directly over the meridian. It is therefore neither ‘ante’ (AM) nor ‘post’ (PM) meridiem. At 12 midnight it also neither AM nor PM.

Ways to avoid confusion with 12:00 AM / PM

One way around this conundrum is to use a different way of communicating the time. If AM and PM is confusing use a time measurement that actually has meaning. Try using ‘12 noon’ or ‘12 midnight’. This also lacks precision and is a mouthful of words. Using the 24-hour clock, or what Americans refer to as ‘Military Time’, adds precision, is easy to say, and boosts your addition and subtraction skills.

Midnight = 00:00
Noon = 12:00

Easy, huh? Not everyone uses the 24-hour clock, though.

Is 12:00 noon 12 AM or PM?

Lack of precision is fine if we are arranging a work meeting or a time to catch up for a coffee, but if we are arranging something that could happen around midnight or noon (for example a flight or train journey) we need to know exactly what time we are talking about.

Web sites, computer systems, timetables all need to be 100 percent accurate and have no ambiguity. The 24-hour military time clock solves this, but many cultures work in AM/PM, so it is helpful to have an answer to whether noon is AM or PM.

AM PM When Is Noon?

12:00 noon is 12 PM – Why?

Although based on the definitions of AM & PM there is ambiguity as at 12:00 noon the sun is neither before or after the meridian it is on the meridian, we can clearly answer what it is just before and just after passing the meridian. Just before 12:00 noon is AM and just after is PM, so lets take a look at both cases – how it works if 12:00 noon is AM and if it is PM. Let’s try both and see which makes most sense:

  • If 12:00 noon is 12:00AM
    Time would progress as: 11:59AM, 12:00AM, 12:01PM.
    This does not look right as 12 o’clock starts as AM then goes to PM.
  • If 12:00 noon is 12:00PM
    Time progresses as: 11:59AM, 12:00PM, 12:01PM.
    This looks right as all minutes in the hour have the same PM indicator.

Hooray! We have solved the problem! We have something that makes sense and can be explained, but how does this relate to reality, how companies use time in their web sites, software systems and services?

Common use of AM PM in Business, Web Sites and Software

Returning to our earlier point that there are no established standards for AM and PM, let’s look at some airport and train times as well as popular calendar software and see if they agree that noon is 12:00PM. We chose the busiest airport and train station in the US and the most popular calendar software:

Hello to New Jersey Transit! You keep being you!

Atlanta, JFK airport, Newark Liberty International Airport (and every other airline we checked), Microsoft Outlook and Google calendars all represent the hour of 12 noon to 12:59 as PM, reinforcing the answer that noon is 12:00PM and providing the joke that all NJ Transit trains from 12:00AM-12:59AM are in fact 12 hours late!

Is noon AM or PM, how Outlook deals with this.

Outlook (and Google) use PM for noon.

Is 12:00 midnight AM or PM?

Using the same thinking as for PM, we all know that 1:00AM is in the morning. One minute before this must be 12:59 and as the sun is definitely before the meridian (ante meridien), so it is 12:59 AM. So, the early hours of the morning are 12:01-12:59AM and midnight is therefore 12:00AM. Yet, is 12:00AM Tuesday midnight on Monday or midnight on Tuesday? Is it night or is it morning?

Is 12:00AM Tuesday midnight on Monday or Tuesday?

Midnight Confusion – When is 12:00AM Tuesday 

Imagine being asked to pick someone up from the airport at 12:00AM Tuesday.

The 24 clock is clear that 00:00 Tuesday is the beginning of Tuesday, or midnight on Monday. It is also clear that 24:00 Tuesday is midnight on Tuesday. However, the 12 hour clock format is ambiguous. 12:00AM Tuesday could be thought of as the middle of the night on Monday or Tuesday. For the sake of the friend waiting at the airport, it is important to get this right!

One way to avoid the problem would be for the friend to ask to be picked up at 12:01AM Tuesday, but this doesn’t work for a business computer system or business web site. We need an accurate answer to this.

Who uses the 12-hour clock format

The 12 hour clock time format using AM and PM is used in North America (United States, Canada and Mexico) , Australia and 14 other nations including Egypt, India, Ireland, New Zealand, Pakistan and Saudi Arabia. However, the 12 hour analogue clock is used all over the world, so really we all use the 12 hour clock time to some extent.

Why are there 24 hours in a day?

The prevailing thought is that it is the Egyptians that created the 12 hour clock time format. Egyptians used base 12 (duodecimal) for counting, they literally counted on their fingers, but not counting individual fingers, they counted the joints on the fingers (excluding thumbs). If you look at the palm of your hand and count between the creases in your fingers you’’ see there are 3 joints, and with 4 fingers you count to 12. With two parts of the day, morning and afternoon / evening, we have 24 hours in the day.


In answer to the questions posed:

  • What does AM PM stand for?
    – AM means Ante meridiem, after midnight
    – PM means Post meridiem, after midday
  • Is noon AM or PM?
    Technically noon is neither AM or PM, but the most sensible and most commonly used time for noon is 12:00PM.
  • What do businesses, web sites and software use?
    Most, but not all businesses, web sites, software and the most popular calendar software uses 12:00PM as noon.
  • When is 12:00AM?
    12:00AM is the start of the day, so midnight of the day before.
  • How does the 12 hour clock time format work?
    The 12 hour clock runs as follows:
    12:00AM, 1:00AM….11:00AM, 12:00PM, 1:00PM….11:00PM, 12:00AM the next day.
  • Who uses the 12 hour clock time format?
    There are 18 countries around the world that use the 12 hour clock.
  • Why are there 24 hours in a day?
    It is believed the Egyptians divided the day into two sets of 12 hours as they counted using base 12.

Why does all this matter to Timewatch?

Timewatch develop professional services automation software, including timesheet, resource scheduling, calendar planning, timesheet billing and add-ons for Outlook and Office 365. It is very important that time is precisely represented as any discrepancy is problematic. Over the years, many customers have asked about about the correct representation of AM and PM for noon and midnight as well as whether 12:00AM is at the end of the beginning of the day. This article is provided to all who wish to understand how AM / PM work and why.

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