Expressing dates and times in a clear and unambiguous way helps support writing for a global audience and reduces confusion.
In general, use the following guidelines to format expressions of time:
- Use the 12-hour clock, except if required to use a 24-hour time, such as when documenting features that use 24-hour time.
- Use hyphens in time ranges. Don't add spaces before or after the hyphens.
Recommended: 5-10 minutes ago.
- Capitalize AM and PM, and leave one space between it and the time.
Recommended: 3:45 PM.
- Remove the minutes from round hours.
Recommended: 3 PM.
Expressing time zones
Avoid using time zones unless absolutely necessary. In cases where you need to use a time zone—such as describing real events at real times—use the following guidelines:
- Let the reader know if the time is local to their time, for example, 10 AM your local time.
- If a time zone is necessary, use the timestamp format as seen in the user interface (if available).
- If using a specific time zone, spell out the region and include the UTC or GMT label as a parenthetical. For example, US and Canadian Pacific Time (UTC-8)
- Don't abbreviate the time-zone name.
- In the rare event where the time of an event doesn't change for daylight saving time, use the specific time zone, without reference to UTC.
In general, spell out the names of months and days of the week in full. Give the full four-digit year, not a two-digit abbreviation. If including the day of the week, add it before the month as follows: DAY_OF_WEEK, MONTH_DAY, YEAR.
Recommended: January 19, 2017
Partial dates and abbreviations
When giving only the month and year, don't use a comma.
Recommended: She was hired in January 2017.
In most cases, don't abbreviate the day of the week or the month. However, when conserving space, such as in a heading or table, it's okay to abbreviate the month and the day of the week to their three-letter abbreviations. Capitalize the first letter and do not add a period at the end of the abbreviation.
If you abbreviate, do so for the entire date. Don't mix written-out forms with abbreviated forms in the same date.
Be consistent in where you apply abbreviations throughout your docset. For example, if you choose to abbreviate in table cells, do so in all table cells.
Not Recommended: Mon, September 3, 2018
Recommended: Mon, Sep 3, 2018
Dates in the middle of a sentence
When a MONTH_DAY, YEAR date appears in the middle of a sentence, add a comma after the year.
However, if the date in the middle of the sentence consists of the month and year only, don't use a comma.
Recommended: The January 19, 2017, release of ...
Recommended: The January 2017 release of ...
Why we prefer dates written out
In general, don't express months as numbers unless you don't have the option (in which case, see numeric-only date format). Different regions of the world put parts of the date in a different order for numeric dates. For example, a date written as 04/05/09 means different things in different regions. For example:
- In the UK, 04/05/09 means May 4, 2009, where the order is usually day, month, and then year.
- In the USA, 04/05/09 means April 5, 2009, where the order is usually month, day, and then year.
- In some other parts of the world, 04/05/09 means May 9, 2004. Some regions write the year first, followed by the month and day.
For this reason, we recommend always using words to express dates. Expressing dates in numbers only (using slashes, periods, or hyphens as separators) can be confusing.
Not recommended: 02.12.2017
Not recommended: 12/02/2017
Recommended: February 12, 2017
Recommended: Sunday, February 12, 2017
Numeric-only date format
If you must express a date in numerical date format, use the format YYYY-MM-DD, and separate the elements using hyphens. This conforms to ISO 8601 international standards for numerical date format.
Additionally, if you have a choice of what date to write (such as in a fictional example), then choose a calendar day greater than 12 to differentiate it from the month.
Not recommended: 04/06/2017
Expressing divisions of the year
Avoid referring to seasons. Spring in the northern hemisphere is fall (autumn) in the southern hemisphere. Instead, use the month, quarter, or temperature (if relevant).
Not recommended: During summer months, data centers face a higher risk of cooling failures.
Recommended: During warmer months, data centers face a higher risk of cooling failures.
Not recommended: In winter, data centers experience higher traffic volume.
Recommended: In November and December, data centers experience higher traffic volume.