The Editor's Manual
Grammar, usage, punctuation, and style resource for editors, writers, and learners of the English language.
Use commas before and after the year in the American date format (May 1, 2021) but not in British (1 May 2021). No comma is needed when only the month and year are specified (May 2021).
American date format is month-day-year (May 1, 2021); British is day-month-year (1 May 2021). Use commas between day and year in American English; no commas are needed in dates in British English.
To show the exact date, spell out the month, and write the day and year in numerals (May 1, 2021, or 1 May 2021). Don’t place a comma between month and year (May 2021). Spell out the day when it stands alone.
Write years in numerals. Say the year in two parts: the first two and then the second two digits. In words, write the year as it would be pronounced.
Centuries are written in either numerals or words (“the 1800s,” “the 19th century,” or “the nineteenth century”). No apostrophe is necessary before the “s” in “1800s.”
Decades may be written in numerals or words (“the 1990s” or “the nineties”), though numerals are preferred in formal texts. In informal usage, an apostrophe may be used to abbreviate the name of a decade.
On the 24-hour clock, the day is divided into 24 hours designated by the numerals 00 for the first hour and 23 for the last hour. Both hours and minutes are always shown. A colon acts as separator between hours and minutes (16:45 for 4:45 p.m.).
Use numerals or figures to write time with “a.m.” and “p.m.” (6:30 p.m.) and in the 24-hour system (18:30). With “o’clock,” use either numerals or words (2 o’clock or two o’clock). Use words for quarter, half, and whole hours (half past ten).
Use “a.m.” and “p.m.” to indicate exact time, and use numerals instead of words to denote the hour and the minute. These abbreviations are generally lowercased in running text, but they may also be capitalized.
When exact time is important, use numerals with “a.m.” or “p.m.” (“2:33 p.m.”); otherwise, use words (“two o’clock,” “two thirty,” “half past two”). In certain settings, the 24-hour system is used to show exact time (“14:33” or “1433 hours”).