OECD Style Guide (Fourth Edition)

5. Dates and time

Abstract

With membership and engagement around the world, it is important to refer to dates, time and seasons in a simple and consistent way, in order to prevent ambiguity and inaccuracy.

Dates

Do

✔ For dates in technical documents and datasets, use the DD-MM-YYYY format.

✔ For dates in general text, use the day-month-year format. Employ numerals for the day and year and the word for the month, and do not use commas. Use hard spaces between the day and month (15 April 1998).

See also: Abbreviations for days; Abbreviations for months.

Don’t

✘ Use ordinal numbers in dates.

🙁 The event is scheduled for November 15th, 2024, at 2:30 PM Paris time.

🙂 The event is scheduled for 15 November 2024 at 14:30 (UTC+1).

Time

Do

✔ For time, use the 24-hour clock.

✔ Specify time zones if relevant. Refer to https://www.timeanddate.com/worldclock/converter.html for time zone names and abbreviations.

Don’t

✘ Use AM and PM.

🙁 The first session will begin at 10:00 AM, the second at 1:00 PM.

🙂 The first session will begin at 10:00, the second at 13:00.

Centuries and age

• Using numbers (rather than words) and correct hyphenation and capitalisation ensures that century and age are accurately expressed.

Do

✔ Use ordinal numbers for centuries and cardinal numbers for people’s ages.

She turned 40 this year; the 18th century.

Don’t

✘ Use superscript for “th” when abbreviating ordinal numbers to refer to a century.

✘ Capitalise “century” unless in a title or as the first word in a sentence.

✘ Hyphenate the time period in age if it is a predicate adjective.

🙁 The OECD was founded in the 20^th Century.

🙂 The OECD was founded in the 20th century.

🙁 The president is 55 years-old.

🙂 The president is 55 years old.

See also: Hyphenation.

Days of the week and months

Do

✔ Always spell out the name of days of the week and of months in full in texts, titles and subtitles.

✔ If space is limited in a table, figure or graphic, or in social media text, use the abbreviations below.

See also: Abbreviations, acronyms and signs.

Abbreviations for days

Mon.	Monday
Tues.	Tuesday
Weds.	Wednesday
Thurs.	Thursday
Fri.	Friday
Sat.	Saturday
Sun.	Sunday

Abbreviations for months

Jan.	January
Feb.	February
Mar.	March
Apr.	April
May	May (no abbreviation)
June	June (no abbreviation)
July	July (no abbreviation)
Aug.	August
Sept.	September
Oct.	October
Nov.	November
Dec.	December

Seasons

• Seasons are opposite in the southern and northern hemispheres, leading to ambiguity if they are used to refer to time periods.

Do

✔ Refer to months, quarters or years to indicate time periods rather than to winter, spring, summer or autumn.

🙁 The conference was held in spring 2018.

🙂 The conference was held in May 2018.

✔ Refer to seasons if needed for discussions of events in specific locations or weather. Be specific so that location is clear.

🙁 The river is more prone to flooding in winter than summer.

🙂 The Seine is more prone to flooding in winter than summer.

Time periods

• Simple, consistent formatting of time ranges ensures your meaning is clear. Correct capitalisation of time periods allows your readers to distinguish between specific and general terms.

See also: Capitalisation.

Do

✔ Use all four digits of the starting year followed by an “s” (no apostrophe) to indicate a decade.

The 1990s were a decade of rapid technological change.

✔ To express a date range, use all four digits of the starting year followed by a hyphen and all four digits of the ending year.

Prices were stable, then rose moderately in 1998-2001.

✔ For time periods in publication titles, use all four digits of the starting year followed by a hyphen and all four digits of the ending year.

The OECD-FAO Agricultural Outlook 2024-2033 was launched yesterday.

✔ Use context to clarify the number of years covered by the date range.

The 2020-2024 average was 8 trillion bushels a day although output dropped at the end of the four‑year period.

✔ Use a slash mark to indicate a period overlapping two calendar years, such as a fiscal, marketing or academic year.

The 2025/26 school year begins on 1 September.

✔ Refer to quarters (periods of three months) with the full word and an ordinal number. For ranges, refer to quarters with a capitalised letter “Q” followed by 1, 2, 3 or 4 and the year, separated by a hyphen. In tables and figures, refer to quarters with a capitalised letter “Q” followed by 1, 2, 3 or 4 and the year.

Business investment grew robustly in the fourth quarter of 2024.

The firm saw earnings drop Q2 2020‑Q1 2021.

✔ Capitalise specific eras and time periods; use lowercase for general ones.

During the Renaissance, texts from ancient times were rediscovered.

Key differences between English and French

English	French
Centuries
21st century	XXIe siècle
Dates
On 1 and 2 March	Les 1er et 2 mars
Decades
The 1990s compared with the 2020s	Les années 90 comparées aux années 2020
Hours
13:20	13h20
Quarters
Q1#2024 OECD GDP growth continued at a steady pace in the second quarter of 2024	T1#2024 La croissance du PIB de la zone OCDE se poursuivait à un rythme constant au deuxième trimestre 2024.