1. To express exact time, use numerals with a.m. and p.m.
- The train leaves at 2:30 p.m.
2. The abbreviations a.m. and p.m. usually contain internal periods.
- Class is from 8:30 a.m. to 2:00 p.m.
3. When the exact time is not important, words may be used. Whole hours are often followed by the term o’clock.
- Let’s meet at two o’clock.
- The game starts at two thirty.
- I’ll be done by half past two.
4. In the 24-hour system (common in military, transit, and hospital settings), use numerals to express the time in hours and minutes, followed by the word “hours.” When this word is omitted, a colon is generally used to separate hours from minutes.
- The train leaves at 1430 hours.
- The train leaves at 14:30.
5. Don’t use expressions of time like in the morning and at night with a.m. and p.m. or with the 24-hour clock.
- The train leaves at 2:30 p.m.
in the afternoon.
- The train leaves at 14:30
in the afternoon.
- The train leaves at 2:30 in the afternoon.
6. Don’t use the number 12 before the words noon and midnight.
- We slipped out the back door at
Time of day
Time can be written using either the 12-hour or 24-hour system. The abbreviation a.m. or p.m., the word hours, or the term o’clock is generally used after the number denoting the time. In informal communication, just the number is often sufficient to express time.
- The train leaves at 12:17 a.m.
- The meeting is at 0800 hours.
- The phone rings every day at nine o’clock.
- Farley finally woke up at 11 o’clock.
- He got to work at three in the afternoon.
How time of day is written is a matter ofrather than grammar. Choose a style appropriate to your field, and follow it consistently throughout the document.
Various style manuals suggest different ways to write the time. Discussed in this article are the major styles, along with examples.
Numerals vs. words for time
Use numerals with a.m. and p.m. to emphasize exact time on the clock face. Also use numerals to specify time using the 24-hour system.
- Tumkin wakes up at 6 a.m. every day.
- The bus will arrive at 3:10 p.m.
- Debriefing is at 1700 hours.
When the exact time is not important, time is generally expressed in words instead of numerals. This is common in creative and informal writing.
- Lunch will be served at two o’clock.
also 2 o’clock
- Is it almost ten?
- Poco works from nine to five.
- It was ten twenty-five, and the bell hadn’t rung yet.
To express time in quarter, half, or whole hours, without the abbreviation a.m. or p.m., use words instead of numerals.
- The meeting starts at eleven thirty.
- The store will open at half past eleven.
- We should be there by a quarter to four (or a quarter of four).
Style manuals differ in their guidelines on whether to use numerals or words for numbers. For example, while the AP Stylebook suggests using words for single-digit numbers and numerals for 10 and above, the Chicago Manual of Style recommends using words for two-digit numbers as well, and numerals from 100 onward. Pick a style, and follow it consistently.
A.m. and p.m.
Use a.m. and p.m. with numerals to refer to exact time. Note that the abbreviations a.m. (from the Latin ante meridiem, or “before midday”) and p.m. (post meridiem or “after midday”) are most often written as such: in lower case with periods between the letters.
- Class starts at 9:30 a.m. every Wednesday.
- He worked steadily from 2 to 4 p.m.
- The train departs from Bratislava at 10:08 a.m. and arrives at Budapest at 4:19 p.m.
When capitalized, small capital letters (or small caps) are generally used, although this style is less common than lowercase letters.
- You can sing between 9:30 AM and 2:00 PM today.
Maintain consistency in showing both hours and minutes, and using numerals or words.
- Poor: Class is from 10 a.m. to 12:30 p.m.
Better: Class is from 10:00 a.m. to 12:30 p.m.
- Poor: The show starts at 7:00 p.m. and ends at eleven in the night.
Better: The show starts at seven and ends at eleven in the night.
Better: The show starts at 7 p.m. and ends at 11 p.m.
In, the abbreviations for the two halves of the day are sometimes written without periods (or full stops). A period also sometimes replaces the colon between hours and minutes: The train arrives at Paddington Station at 3.30 pm every day.
When aends in an abbreviation, don’t add another period. However, in questions, use a as usual. If the abbreviation is within parentheses after which the sentence should end, add another period.
- We can deliver the couch to you by 4 p.m.
- Can you please deliver the couch by 4 p.m.?
- We can deliver the couch this afternoon (by 4 p.m.
Don’t uselike “in the morning,” “in the afternoon,” and “at night” with a.m. and p.m.
- Incorrect:Poco arrived at 2 p.m. in the afternoon.
Using p.m. already indicates that we’re talking about a time in the afternoon.Correct:Poco arrived at 2 p.m.
- Incorrect:The meeting will start at 9 a.m. tomorrow morning.
Correct:The meeting will start at 9 a.m. tomorrow.
Noon and midnight: a.m. or p.m.?
Prefer to use the words noon and midnight instead of 12 p.m. or 12 a.m.
- Incorrect: The day starts at 12 a.m.
Correct: The day starts at midnight.
- Incorrect: Please send the report by 12 p.m.
Correct: Please send the report by noon.
Don’t use the numeral 12 with the words noon and midnight. Writing the numeral is unnecessary and considered poor style. (It cannot be anything but 12 at noon and midnight.)
- The day starts at
12midnight.The word “midnight” implies that it is 12 on the clock. The numeral “12” is therefore redundant. Although such usage is common in speech, avoid it in writing.
- Please send your report by
The term o’clock, which means “of the clock,” may be used when the exact time is unimportant. Such usage is common and often preferred in everyday speech, creative writing, and informal communication. There is no space between the apostrophe and the word “clock.”
- Oh no, is it three o’clock already?
- The bell rang at two o’clock.
- It’s nine o’clock and still light out.
Either numerals or words may be used with o’clock. Style guides differ in their recommendations. The Chicago Manual of Style, followed by academic and book editors, recommends spelling out the number with o’clock. The AP Stylebook, used in American media and journalism, suggests using numerals.
- Chicago: It was three o’clock in the afternoon when the clocks stopped.
- AP: It was 3 o’clock in the afternoon when the clocks stopped.
When both hours and minutes are expressed, the term o’clock is omitted.
- Incorrect: It’s four twenty o’clock.
Correct: It’s four twenty.
To informally express the hour and the minute both, simply use numbers and omit o’clock. Or you can use numerals with a.m. or p.m. (These abbreviations may be omitted if it is obvious which half of the day you’re referring to.)
- Please be there by four twenty-five.
- Please be there by 4:25 p.m.
- Please be there by 4:25.
Quarter, half, whole hours
In speech and informal writing, time is often expressed in quarter, half, and whole hours.
- It’s a quarter to four (or a quarter of four).
Thea is optional.
- It was half past nine when the train finally arrived.
- The museum is open from nine to six on weekdays.
With whole hours, the term o’clock may or may not be used. Also, since a.m. and p.m. are not used, time expressions like “in the morning” or “at night” are appropriate.
- The Durandians landed in Farley’s backyard at nine o’clock on a Monday morning.
- The Durandians landed in Farley’s backyard at nine in the morning last Monday.
12-hour vs. 24-hour system
Many countries express time using the 24-hour system instead of the 12-hour system. The 24-hour system is also used when confusion between a.m. and p.m. could result in dangerous or costly mistakes—for example, in military settings, hospitals, research labs, airports, and train and bus stations.
- The siren rang at 0413 hours.
That is, at 4:13 a.m.
- Departure is at 16:45.
Clearer than “4:45,” which could mean either morning or evening.
- The patient was in surgery from 11:00 to 14:30.
In general, to write time in the 24-hour system, omit the colon between hours and minutes, and follow the numerals for time with the word “hours.”
- The invasion began at 0823 hours.
Read aloud as “oh-eight-twenty-three hours” or “zero-eight-twenty-three” (military).
- The train departs from Bratislava at 1008 hours and arrives at Budapest at 1619 hours.
Read aloud as “ten-oh-eight” and “sixteen-nineteen.”
A colon is used when the word “hours” is omitted.
- The invasion began at 08:23.
- The train leaves Bratislava at 10:08 and reaches Budapest at 16:19.
Time expressions (noon, midnight, morning, afternoon, evening, night, etc.) are unnecessary in the 24-hour system.
- The train leaves Berlin at 0617 hours
in the morning.The phrase “in the morning” is redundant, since it is already clear which part of day is being referred to.
- It reaches Vienna at 14:45
in the afternoon.
Midnight: 00:00 or 24:00?
Both 00:00 and 24:00 refer to midnight. Use 0000 hours or 00:00 to refer to the start of a day. Use 2400 hours or 24:00 to indicate the end of a given day.
- The operation will commence at 0000 hours on January 16, 2033.
the start of January 16
- Your commanding officer will conduct a briefing from 22:30 to 24:00, after which the operation will commence.
a briefing at the end of the day
Space after numerals for time
Regardless of whether you use a.m./p.m., o’clock, or hours, always use a space after the numerals used to denote the time.
- Rita goes for a run at 6:15 a.m. every day.
- Maya woke up with a start at 5 o’clock in the morning.
- The final shuttle for Mars leaves at 0330 hours.
Specify time zones only when necessary. Periods are not used with abbreviations for time zones.
- The call begins at 10:30 a.m. EST.
- I’ll send you the report by 5 p.m. IST (7:30 p.m. SGT).
- The Durandians landed on Earth at 8:17 a.m. UTC on October 23, 2073.
When spelling a time zone out, you may either capitalize or lowercase the words. The Chicago Manual of Style suggests using lowercase letters; the AP Stylebook suggests capitalization. Always capitalize proper nouns and proper adjectives (names of places or regions).
- All the time frames specified are in Pacific standard time.
- The train arrives at 14:00 (central European time).
- The time shown on our website is eastern daylight time.
- We follow Pacific Standard Time.
- Is that 14:00 Central European Time?
- Is that Eastern Daylight Time?
The correct term is daylight saving time, not daylight savings time.
Time periods and duration
You may use either words or numerals to speak of a duration or a time period. In general, use words for numbers until nine and numerals from 10 onward.
- This movie is four hours long.
- We are going on a 12-day vacation.
- Could you wait five minutes, please?
In Chicago style, use words for two-digit numbers as well. Hyphenate two-digit numbers.
- Our rent is paid for thirty-one days.
- This project will take at least twenty-four hours to complete.
To speak of duration, use for. To speak of a point in time, use since.
- Duration: We have been working on this for/
- Point in time: We have been working on this
for/since 9 a.m.
Useor between–and to show a range.
- Anita worked steadily from 2 to 4 p.m.
- Your order will arrive between 2 and 4 p.m. today.
- Rehearsal is from 8:00 to 9:30 a.m. on Saturday.
Ranges, including those signifying time, may also be written using an en dash.
- The meeting is scheduled for 2:00–3:30 p.m.
- Rehearsal is 8:00–9:30 a.m. tomorrow.
- The journey lasts 3–4 hours.
With the word from, use to, not an en dash. If you do use an en dash, omit the word from.
- Incorrect: We are open from 9 a.m.–5 p.m. on weekdays.
- Correct: We are open from 9 a.m. to 5 p.m. on weekdays. Correct: We are open 9 a.m.–5 p.m. (or 9–5) on weekdays.
Units of time
With abbreviated, always use numerals. In scientific and technical writing, use the SI symbols for , which are h, min, and s (for hour, minute, and second). Periods are never used with SI units.
- Duration of the experiment: 3 h
- Lap time: 443 s
- Time taken: 4 min 43 s
In nonscientific and nontechnical writing, units of time are often abbreviated to hr., min., and sec. A period usually follows the unit. Use numerals instead of words with abbreviated units.
- Time taken: 25 min.
- Project duration: 9 hr. (or 9 hrs.)