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Neha Karve
Summary
Follow these generally accepted guidelines to use a.m. and p.m. (or AM and PM) correctly in formal writing:
- Use the abbreviations a.m. and p.m. to indicate exact time.
- Use a.m. to refer to a time of day before noon, and p.m. to speak of a time between noon and midnight.
- Use numerals or figures instead of words to denote time with a.m. and p.m. (
eleven/8 a.m.) in formal texts. - Although both hours and minutes are often presented in formal or official documents, specifying the minutes is optional for whole hours (8 a.m. or 8:00 a.m.).
- In running text, a.m. and p.m. are usually lowercased with periods after the letters of the abbreviations; however, they may also be capitalized (8:01 a.m. or 8:01 AM).
- Avoid using expressions of time like “in the morning” and “at night” with a.m. and p.m. (8 a.m.
in the morning). - Use the words noon and midnight instead of 12 p.m. or 12 a.m.
What do a.m. and p.m. mean?
The abbreviation a.m., which comes from the Latin ante meridiem (before midday), designates the first 12-hour period of the day. The second half of the day takes the abbreviation p.m., from post meridiem (after midday).
Examples
- Tumkin wakes up at 6 a.m. everyday.
in the morning (before noon)
- The staff break for lunch at 1:15 p.m.
in the afternoon (after midday)
When to use and how to write a.m. and p.m. is a matter of style rather than grammar. Discussed here are commonly accepted guidelines.
When to use
Use the abbreviations a.m. and p.m. to emphasize exact time. Specifying the exact time is preferred in formal contexts, such as in official communication.
Examples
- Please be present at 10:30 a.m. on Tuesday.
- All goods must leave the warehouse by 2 p.m.
- The deadline to submit the application has been extended to 4:45 p.m.
- The doctor is available from 11:00 a.m. to 4:30 p.m. on weekdays.
When the exact time is not important, and in informal contexts, such as in everyday speech, the abbreviations a.m. and p.m. are often omitted. In particular, when it is clear which half of the day is being referred to, using these abbreviations may sound unnecessarily formal. Speakers then use phrases like o’clock, half past, and a quarter past, or simply the numbers for time.
Examples
- It’s eleven o’clock, and I still haven’t finished my report.
Presumably, the listener knows whether the speaker is referring to eleven in the morning or the evening.
- I’ll be done by half past ten.
- We break for lunch at a quarter past one.
- I’ll be there by 2:30.
- They work from nine to six every day.
Numerals or words?
With the abbreviations a.m. and p.m., always use numerals or figures instead of words to denote time in formal writing.
Examples
- The bell rang at 1 p.m.
- The conference began at 11:30 a.m.
- We have a meeting at 4 p.m. today.
- Please submit your applications by 10 a.m. on Monday.
To show approximate rather than exact time, you may omit a.m. or p.m., and use words instead of numerals.
Example
- We worked from one to three thirty in the afternoon.
In informal and creative writing, words are often used instead of numerals to show the time.
Examples
- Informal: It was just three p.m. but dark outside.
Formal: Submit your reports by 3 p.m. - Informal: We left the coroner’s office at nine PM.
Formal: The coroner’s report arrived at 9 PM.
Hours and minutes
In a time reference using a.m. or p.m., always indicate the hour. Showing minutes is optional. Where exact time is important, such as in official, academic, and technical writing, prefer to show both hours and minutes.
Examples
- Class starts at 10 a.m. / 10:00 a.m.
- Class is from 10 to 11 a.m. / 10:00 to 11:00 a.m.
- Anita works from 9 a.m. to 6 p.m. / 9:00 a.m. to 6:00 p.m.
Caution
If you show minutes for one time reference, show them for all references in that context.
Examples
- Poor: Class is from 9:30 a.m. to 1 p.m.
Better: Class is from 9:30 a.m. to 1:00 p.m. - Poor: I’m busy from 2 to 4:00 p.m. today.
Better: I’m busy from 2 to 4 p.m. today.
Use of periods and capitals
In general, use lowercase letters with periods after the letters of the abbreviations a.m. and p.m., particularly in running text. These abbreviations are sometimes capitalized—for example, in signs and notices. The periods are then omitted.
Examples
- Our ship sails at 3:15 p.m. on Thursday.
- The local coffee shop is open from 7 a.m. to 9 p.m. every day.
- Open: 7 AM to 9 PM
sign outside a coffee shop
Tip
Most style manuals, like the Chicago Manual of Style, the AP Stylebook, and the APA Publication Manual, recommend using lowercase letters for a.m. and p.m., with periods between the letters of these abbreviations.
If a.m. or p.m. appears at the end of a sentence, don’t use two consecutive periods. Use the same period to mark both the abbreviation and the end of the sentence.
Example
- Incorrect: All the clocks stopped at 12:33 a.m..
Correct: All the clocks stopped at 12:33 a.m.
If you do capitalize these abbreviations in running text, prefer to use small capital letters (small caps).
Examples
- Our space shuttle leaves at 3:15 PM on Thursday.
- My phone is switched off from 6 PM Friday to 8 AM Monday.
In British usage, periods are sometimes omitted in lowercase abbreviations: Colin drinks tea at 4 pm every day.
Space before AM and PM
Always insert a space after the numerals used to denote the time, regardless of whether you lowercase or capitalize the abbreviations a.m. and p.m.
Examples
- From 2 to 3 a.m. every day, Poco practices playing the guitar.
- The Durandians landed in Farley’s garden at 8:33 a.m. last Monday.
- Let’s meet at 9:30 AM on Monday.
- Matinee: 12:30 PM
Noon and midnight
Noon is neither a.m. nor p.m., since “a.m.” refers to times before noon and “p.m.” to those after. Simply use the words noon and midnight instead of 12 a.m. or 12 p.m. Not only is this correct, it is also less confusing.
Examples
- Incorrect: It started raining at 12 p.m.
Correct: It started raining at noon. - Incorrect: All the alarms went off together at 12 a.m.
Correct: All the alarms went off together at midnight.
Caution
Placing the numeral 12 before noon or midnight is redundant (the time is always 12 on the clock at noon and midnight). Although such usage is common in speech, avoid it in writing.
Examples
- It was
12midnight, but our work wasn’t over yet. - Measure the length of the shadow at
12noon.
Expressions of time
Since a.m. and p.m. clearly indicate which part of the day is being referred to, expressions of time like in the morning, this afternoon, and tonight are unnecessary with these time abbreviations. Although such expressions are common in speech, avoid using them with a.m./p.m. in formal writing.
Examples
- Poor: Maya wakes up at 6 a.m. in the morning every day.
Better: Maya wakes up at 6 a.m. every day. - Poor: Tumkin’s flight is at 2 p.m. on Sunday afternoon.
Better: Tumkin’s flight is at 2 p.m. on Sunday. - Poor: Farley called me at 4 a.m. this morning.
Better: Farley called me at 4 a.m. today. - Poor: Our store is open till 6:30 p.m. in the evening.
Better: Our store is open till 6:30 p.m.
Consistency in usage
While writing time of day, don’t mix styles within a single context. Stay consistent in usage with relation to a.m./p.m., numerals, and hours and minutes.
Examples
- Poor: The bus leaves Butterworth at 9:30 a.m. and reaches Melaka at 4 o’clock.
Better: The bus leaves Butterworth at 9:30 a.m. and reaches Melaka at 4:00 p.m.
Better: The bus leaves Butterworth at half past nine in the morning and reaches Melaka at four in the afternoon. - Poor: Farley slept at 1:00 a.m. and woke up at six.
Better: Farley slept at 1 a.m. and woke up at 6 a.m.
Better: Farley slept at 1:00 a.m. and woke up at 6:00 a.m.
Better: Farley slept at one and woke up at six.
Considerations of formality
In formal texts, prefer to use a.m. and p.m. with numerals for time. In informal usage, such as in speech and creative writing, using words can sound more natural.
Examples
- Formal: The first shift is from 9 a.m. to 5 p.m.
Informal: I work from nine to five on weekdays. - Formal: Departure is at 11:25 a.m.
Informal: We leave at eleven twenty-five. - Formal: The meeting starts at 10:30 a.m.
Informal: Is it half past ten already?
Tip
In scientific writing, the 24-hour system of time is often used instead of the 12-hour system. On the 24-hour clock, the day is represented by a single 24-hour period instead of two 12-hour periods: 6 a.m. is 06:00, and 6 p.m. is 18:00.
