A.M., P.M., a.m., p.m.: What Is the Correct Time?

Pam wrote to me to settle a debate between the younger and the older employees in her office. Her brief question was this:

4pm or 4:00pm?

My answer: Neither!

Both of Pam's renderings are incorrect. She needs to insert periods and a space before the abbreviation, like this:
4 p.m. or 4:00 p.m.

In email, many people seem to be dropping both the periods and the space, but don't follow the crowd. The prominent style guides do not support that choice. Here is a sampling of recommendations:

The Associated Press Stylebook:
4 p.m.

Microsoft Manual of Style for Technical Publications:
4 P.M.

The Chicago Manual of Style and Garner's Modern American Usage:
4 p.m. or 4 PM (with PM in small capitals)

The Gregg Reference Manual:
4 p.m. or 4 P.M. (with PM in small capitals)

Whatever style you choose, be consistent. I always use lowercase letters: 4 p.m.

Pam's coworkers were apparently arguing about whether to include the zeros. Omit zeros when the time is on the hour, but include them in a list of varying times like this one:

7:00 a.m. Registration
7:30 a.m. Breakfast
8:00 a.m. Announcements
8:15 a.m. Speaker

Pam, it's time for you and your coworkers to pitch in and get a style manual. See the recommendations on my website.

Does your style guide recommend a different approach to time? If so, please share it here.

Lynn
Syntax Training

Comments

[Srikanth]

Great, never thought about it before. Thank you!

[Conrado Calvet]

I prefer use the 24 hr clock for schedulling, it´s a good option and it´s easier avoid misunderstadings for the people whom just pass a eye in the schedule.

Why dou you think Lynn?

Kind Regards
Conrado

[Lynn]

I think the 24-hour clock is an excellent idea. I find, though, that many people in the United States prefer a.m. and p.m., particularly if their business does not run 24 hours a day.

[Lisa]

My style manual is the American Medical Association's Manual of Style, which avoids using punctuation in abbreviations (up to and including MD, eg, and ie). It's one of the hardest things for people to get used to when they start writing at my company. The other hard thing for people to remember is not spelling out numbers unless they start a sentence -- even numbers under 10! You can see a brief overview of AMA style here:
http://www.docstyles.com/archive/amastat.pdf

[Lynn]

Lisa, thanks so much for sharing the information and a resource. It is helpful to know about the differences.

I can understand how new employees struggle with the punctuation and number rules. I am glad you have a style sheet to support the new writers--and the rules.

[Sue]

What about a period of time? If a function runs from 5 p.m. - 7 p.m. Or is it 5 - 7 p.m.?

[John]

Actually, in a business context, it is best to ALWAYS use zeros (4:00). Though this rule can "bend" for native speakers, if you are working with internationals, it's better to have a consistent rule that is applied at all times.

Also, when using the 24-hour clock (a norm for those outside North America), you should use a leading zero to avoid confusion (04:00 rather than 4:00).

Finally, it's important to avoid being draconian when writing emails. A new register has actually been created for emails: neutral. So there is formal for letters and legal/offical matters, informal for person correspondence and neutral for business email correspondence.

[dyhlon]

What about if the 4 P.M. is at the end of the sentence? Do you need to put another period?

[Lynn Gaertner-Johnston]

Sue, one mention of "p.m." is sufficient when your meaning is obvious.

John, thank you for mentioning international audiences and their needs.

Dyhlon, you need only one period at the end of the sentence. Two periods would be incorrect.

Lynn

[Christine Clinton]

I also write AM and PM without the periods or the spaces. I always thought that writing A.M. or a.m. or P.M. or p.m. was not the correct way of writing that. I guess I am an old stick in the mud, and since I hate change, or newer ways of doing things, I am going to stick with writing AM and PM. It might be wrong, or grammatically incorrect, but it is what I am used to.

[Lynn Gaertner-Johnston]

Christine, you are not an old stick-in-the-mud. You are on the cutting edge! Only some style manuals have begun to leave out the periods in question. My "Handbook of Business English," first published in 1914, includes them.

You didn't know how modern you are.

Lynn

[Ben]

Is it proper to write: At 4p.m. this afternoon we will be meeting. . .
Is it improper to add the word 'afternoon' if you have stated that the time is 4 p.m.?

[Lynn Gaertner-Johnston]

Hi, Ben. It is redundant to write "4 p.m. in the afternoon." However, "4 p.m. this afternoon" does clarify which afternoon (for example, not tomorrow afternoon).

A better choice is "4 p.m. today."

Lynn

[Mister Nice Guy]

Any answer to:
"What about a period of time? If a function runs from 5 p.m. - 7 p.m. Or is it 5 - 7 p.m.?"

[Lynn Gaertner-Johnston]

Hi, Mister Nice Guy. I belatedly answered Sue's question on May 1, 2010:

One mention of "p.m." is sufficient when your meaning is obvious.

Lynn

[Sally Kelly]

What is the correct way to write 12 midnight or 12 noon

Is the 12 noon, 12:00p.m. or 12:00 a.m.?

[Lynn Gaertner-Johnston]

Sally, many reference books recommmend simply "midnight" or "noon." However, if you are entering that time with a list of other times, use "12 midnight" or "12 noon." Using the number alone with a.m. or p.m. can be confusing in some contexts, so avoid that approach.

Lynn

[Mircalla]

Hi Lynn,

I've been searching online for the proper way to list an event day, date and time and came across this blog post. Perhaps you can help? Is the following the correct way:

XYZ panel takes place on Tuesday, September 13, at 11:00 a.m.

Thanks in advance for any clarification!

[Lynn Gaertner-Johnston]

Hi, Mircalla. Your sentence looks fine. You would also be correct to write "11 a.m." (without the zeros), especially if you have no other times to list.

Lynn

[John Snakenborg]

Did you notice the time stamps here - capital letters, no punctuation. Now what?

[Lynn Gaertner-Johnston]

Hi, John. Interesting question! It appears that TypePad, the host for this blog, follows the style of "The Chicago Manual of Style" and "Garner's Modern American Usage" (see above), more or less.

[Pa]

Dear Lynn,
How would I write a time when asking a question?

Example: Are you available at 4p.m.?

Would I have the periods between the "p" and the "m" and then put the question mark?

[Lynn Gaertner-Johnston]

Your example is almost correct. You need a space between the 4 and the p, like this:

Are you available at 4 p.m.?

Lynn

[Todd]

Hi Lynn!

How would time zone abbreviations fit into this equation?

Thanks!

[Lynn Gaertner-Johnston]

Hi, Todd. Search for my post "It's About Time: Clock Time" in the search box at upper right.

Lynn

[Todd]

Thanks!