Chicago Manual of Style 17, published 2017 (usually used for books) is in blue and AP Stylebook 2020–2022 (usually used for news media) is in orange. Black text indicates the two systems agree.
This page originally published March 2, 2016. Thoroughly updated August 1, 2022.
Chicago and AP agree, do not use st, nd, rd, or th on date, even though you pronounce it. 1
Month Date Year
Chicago style: The concert will be February 10, 2022, at Carson Music Hall. 2
AP style: The concert will be Feb. 10, 2022, at Carson Music Hall. 3
(AP note: If it’s this year, don’t include the year.)
Day Month Date Year
Day Month Date
Chicago style: Please call before October 1 to reserve your room. November 12 was a normal day. 2
AP style: Please call before Oct. 1 to reserve your room. Nov. 12 was a normal day. (Note, AP spells out the month unless a specific date is mentioned. So it’s Oct. 1 and Saturday, Oct. 1, and Oct. 1, 2022, but October 2022 and “in October.”) 3
November 2016 was a strange month. 6
Note: Preferred over November
Regarding “of,” CMS 17 includes the example “April 2021” in 6.38 and does not use “of” after the month anywhere on their site. And 5.250 (written by Bryan A. Garner) under “of” says, “Prefer June 2015 over June of 2015.” It is also covered in Bryan A. Garner, Garner’s Modern English Usage, 4th ed., p. 246, which states, “February 2010 is better than February of 2010.” (A big thank you to Glenn Gladfelder in July 2022 for noticing that “of” is not wrong according to CMS—it’s just less preferred. He is correct! I have updated this text to reflect that.)
AP only covers it in their “Ask the Editor” section here, where they say, “No of. Just March 2020. We may not have an explicit entry on that point, but an example is below (January 2016).”
They left on Tuesday for their vacation. 7
Chicago style: His birthday is on the seventh. His birthday is on the twenty-first. We will be there the first through fifteenth of next month. 10
AP style: His birthday is on the seventh. Her birthday is on the 21st. We will be there the first through 15th of next month.
CMS and AP agree, use numerals usually. But if the year is at the beginning of a sentence, CMS spells it out but AP does not.
Both agree: The transition will take place in 2025.
But CMS beginning of sentence: Twenty twenty was a year like no other. or Two thousand twenty was a year like no other. (CMS recommends rewording in these situations to avoid having the year begin the sentence.) 12
AP beginning of sentence: 2020 was a year like no other. (AP usually spells out numbers at the beginning of a sentence, except for years.) 13
Holiday with Year
Season with Year
In fall 2008 I took my first class. 15
Exception: With CMS, in journal citations, capitalize the season. 16
1. First Last, “Article Title,” Journal 36, no. 7 (Fall 2000): 25–31.
Dates as adjectives
Even if a date is used as an adjective, the comma rules don’t change.17
Chicago style: The February 10, 2022, concert was a success.
The Thursday, February 10, concert was a success.
The February 10 concert was a success.
AP style: The Feb. 10, 2022, concert was a success.
The Thursday, Feb. 10, concert was a success.
The Feb. 10 concert was a success.
Both: The February 2022 concert was a success.
Date with “on”
Chicago style: not specifically covered
AP style: Omit “on” with a date if it makes sense without it: The event will take place Nov. 16. (not “
on Nov. 16” if possible) 18
In regular running text:
Chicago style: Do not abbreviate months or days of the week within regular text. 2
AP style: Spell out months with 5 letters or fewer within regular text. 19
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
Days of the week: do not abbreviate.
In tabular material (lists, charts, tables, etc.):
Chicago style—There are three abbreviation systems listed in CMS. This is the first, and it is their preferred method. Spell out months with 4 letters or fewer. 20
Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. (tabular only)
Sun. Mon. Tues. Wed. Thurs. Fri. Sat. (tabular only)
Again, these abbreviations are OK for tabular matter only, such as lists, charts, and tables. DO NOT ABBREVIATE in regular running text.
AP style—In tabular material only (lists, charts, etc.), use these 3-letter forms with no period: 19
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec (tabular only)
Sun Mon Tue Wed Thu Fri Sat (tabular only)
Again, these abbreviations are OK for tabular matter only, such as lists, charts, and tables. Within text, see above under “In regular running text.”
Chicago and AP styles: the class of ’16 21
Chicago style specifies this is for informal use only, and the full year is preferred formally: the class of 2016. 22
Make sure to use an apostrophe/right single quote ’, not a left single quote ‘. Your software will assume you want a left single quote at the beginning of a word, so you have to go back and change it manually!
Note, AD goes before the year, but the other abbreviations go after the year. AP uses periods, Chicago does not.
BC and AD – “before Christ” and “anno Domini” (in the year of our Lord)
BCE and CE – “before the Common Era” and “of the Common Era”
(There are also others used for different purposes.)
If “from” or “between” precedes it, never use an en dash
from 2002 to 2004
between 2010 and 2015
Otherwise, you may use an en dash, which means “up to and including.”
Usually repeat only two digits.
the 2005–10 crisis
the winter of 2014–15
But repeat only one digit if it’s 01-09
Repeat all digits if the century changes
Repeat all digits if one is an “00”
the years 2000–2001 were . . .
Repeat all digits if BC or BCE is used
To indicate the end of one year leading into the next, you may use a slash if you wish. Or just use an en dash or spell out in words.
the winter of 2015/16
the 1998/99 school year
For a book or chapter title, it’s best to repeat all digits. (If you’re just citing a book title, cite however it appears on the book.)
Diaries from the Trails, 1850–1855
You may also use an en dash when months and dates are included if context allows, as long as “from” or “between” does not precede it.
I will be gone December 2016–February 2017. but gone from December 2016 to February 2017.
The articles appeared January 29–March 20.
The May 14, 1966–January 10, 1967 issues are missing.
Chicago notes regarding using centuries as adjectives
early twentieth-century fashion but fashion from the early twentieth century 27
mid-twentieth-century fashion but fashion from the mid-twentieth century 28
late twentieth-century fashion but fashion from the late twentieth century 27
the midcentury home 29
Chicago and AP styles: the 1990s 30
(Make sure to use an apostrophe/right single quote ’, not a left single quote ‘. Your software will assume you want a left single quote at the beginning of a word, so you have to go back and change it manually!)
1980s-style fashion and dressed 1980s-style 35
The first two decades of a century must be treated differently.
the first decade of the twentieth century 31
the years 1900–09 31
Do not use “
the 1900s” to refer to just the first decade, because it could also refer to the whole century. 31
AP style does not have an official ruling. Use whatever is clearest.
Note: Some experts consider a decade to begin in 1901, 2001, etc., but most readers consider a decade to begin in 1900, 2000, etc. Go with author/subject preference on this.
“the 1910s” isn’t great, but can be used if necessary. 31
the second decade of the twentieth century 31
the years 2010–19 31
do not use “
the teens.” 31
AP style does not have an official ruling, but they do not like “the teens” either. Use whatever is clearest. 37
the ’00s 38
the first decade of the twenty-first century 31
the years 2000–09 31
do not use “
the 2000s” to refer to the decade only 31
AP style does not have an official ruling, but tends to use “the 2000s” 39
I tend to go with author preference on this. If the author has “the 2000s” and it’s clear they are talking about the decade, I feel it’s unnecessary to change. Check for clarity and adjust as needed.
The following is covered in Chicago Manual of Style only:
Per Chicago style. If the intro phrase is short, no comma is necessary unless it’s confusing without it. But you can still use a comma if you like. CMS approves both styles. They are not clear on exactly what “short” means, so use your judgment and make sure it’s clear. The shorter the phrase is, the less likely it will require a comma.
In 2015 I bought a new computer. (or In 2015, I . . . )
Before 1862 the troops were unorganized. (or Before 1862, the . . . )
On October 25 she won the lottery. (or On October 25, she . . . )
After January her health improved. (or After January, her . . . )
In 2003, students received new textbooks. (because “2003 students” could be confusing.)
In May, Jane sold her house. (because “May Jane” is confusing.)
After Monday, rush hour will be a nightmare. (Without the comma, the sentence is ambiguous.)
Note, you still need a comma before and after the year in month-day-year format, because you always do.
On October 25, 2015, he joined the company.
Note, this rule applies to all introductory adverbial phrases, not just the ones with dates.
After the divorce she left the city. (or After the divorce, she . . . )
but Before leaving, Jane said goodbye. (because “Before leaving Jane” is confusing.)
a decades-old fight but the fight was decades old
a centuries-old document but the document was centuries old
a ten-year plan but the plan was for ten years
a six-month wait but the wait was six months
a three-day weekend or a three-day-long weekend but the weekend was three days long
Alternate (chiefly British) style: day-month-year style
Standard in British English. Can be used in US English, but primarily for works with many full dates. Most US readers are used to the other style, so it can be distracting.
No commas needed.
The events of 5 April 2012 and 17 June 2015 were oddly similar.
Slashes, dashes, and periods
Avoid these in formal publications because US puts month first, but many other countries put day first (e.g., Canada, UK).
3/26/14 3-26-14 3.26.14 (informal use only)
ISO standard date format
If an all-numeral form is needed, use the ISO standard date format. Not recommended for formal prose, but allows dates to be sorted properly in lists and spreadsheets.
2014-03-26 (for lists or informal use only)
Chicago Manual of Style, 17th Edition, 5.83, 6.38, 6.69, 6.78, 6.107–8; 7.89 under “numbers, spelled out,” “century,” “old,” “style,” “prefixes: mid”; 8.72–73, 8.88–89, 9.29–36, 9.64, 10.38–40. (Not used here but relevant: 6.68, 6.79, 9.34)
Associated Press Stylebook 2020–22, months, years, dates, A.D., B.C., century, decades
Chicago style dictionary is Merriam Webster’s Collegiate Dictionary, Eleventh Edition (MW11)
AP style dictionary is Webster’s New World Collegiate Dictionary, Fifth Edition (WNW5)
- CMS 2017, 9.31; AP 2022, dates
- CMS 2017, 9.31, 6.38
- AP 2022, months, years
- CMS 2017, 6.38
- AP 2022, months, days of the week
- CMS 2017, 6.38; AP 2022, months
- CMS 2017, 8.88; AP 2022, days of the week
- CMS 2017, 6.38, 8.88; AP 2022, months
- CMS 2017, 7.89 “mid,” AP 2022, mid-
- CMS 2017, 9.31
- AP does not have an entry for this, but their “Ask the Editor” advises us to follow their ordinal number rules in this situation: spell out first through ninth, and use numerals for 10th and above. This is the only exception to not using st, nd, rd, or th on the date. APStylebook.com, search “ordinal date” and read the “Ask the Editor” answers.
- CMS 2017, 9.29
- AP 2022, years
- CMS 2017, 6.38, 8.89; AP 2022, holidays and holy days, AP Ask the Editor, “Christmas Day 1929,” https://apstylebook.com/ask_the_editors/15739.
- CMS 2017, 8.88; AP 2022, seasons
- CMS 2017, 15.9
- CMS 2017, 6.38; AP 2022, months, Ask-the-Editor
- AP 2022, “on”
- AP 2022, months
- CMS 2017, 10.39
- CMS 2017, 9.30; AP 2022, numerals: dates, years and decades
- CMS 2017, 9.30
- CMS 2017, 9.34, 10.38
- AP 2022, B.C., A.D.
- CMS 2017, 9.32
- AP 2022, century, historical periods and events
- CMS 7.89: century
- CMS 7.89: century, and prefixes—mid
- CMS 7.89: prefixes—mid
- CMS 2017, 9.33; AP 2022, decades
- CMS 2017, 9.33
- AP 2022, decades
- CMS 2017, 7.89: prefixes—mid; AP 2022, mid-
- CMS 2017, 9.33; 7.89 prefixes: mid
- CMS 2017, 7.89; AP: not specifically covered but this follows their style
- CMS 2017, 8.73
- AP Ask the Editor, search “1910s” and “the teens”
- CMS Shop Talk, 2019, https://cmosshoptalk.com/2019/09/10/decades-cmos-9-33/
- AP Ask the Editor, search “2000s” and “00s”
- AP Ask the Editor, search “2010s”