Date/Time Patterns

Last updated: 2018-May-14

Patterns Introduction

Pre-requisite topics to read:

A date-time pattern is a string of characters in which fields representing date and time symbols are combined together with necessary "literal" strings that are used as is.

There are two types of substrings that are combined in a pattern:

There are three aspects to patterns: 

To demonstrate how this work with examples, see the spec Date Format Pattern Examples.

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Synchronizing Date/Time Names and Patterns

There is a tight coupling between the date/time patterns and the names that are used for date/time elements, described in Date/Time Names. Therefore, when supplying the data, it requires coordination between what you supply as the names and your intention on which name to use in patterns.

When to use Standalone vs. Formatting

Some types of names have two styles and these are differentiated in the survey tool section headings a Formatting and Standalone.

Using the month names as examples:

Following are examples of differences and implications based on language:

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Basic Time Formats

The standard formats include four basic time formats. See Survey Tool Formats-Standard-Time formats

Using 24 hour vs 12 hour symbols: The symbols you use in time format patterns depend on whether the main country/region of the language uses 12-hour time or 24 hour format.

If a non-default country/region use a different time format than the default country/region for the language, then this difference should be added for the sub-locale. Also see Regional variants. 

For example, if es (= es_ES, Spanish as used in Spain) uses 24-hour time formats, but es_US (Spanish as used in United States) uses 12 hour time formats, then es would use "HH:mm/H:mm" and es_US would use the "h" formats as described above. .

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Basic Date Formats

The standard Date formats include four basic formats. See Survey Tool Formats-Standard-Date formats. (Note that the Month symbol especially may vary (M vs MM, or MMM vs LLL). For more information, see Date/Time Symbols.)

Additional Date-Time Formats

The basic formats as described in above sections provide a small subset of the combinations. To expand to fully cover all variations of date and time formats, a skeleton format is provided that uses the Date/Time Symbols (without order or punctuation) to indicate what fields are desired. 

An example usage of the flexible formats would be: a software program only needs the year and month information, the flexible pattern yMMM would be used to provide the desired year and month formatting as shown in the English and Japanese examples in this table. 

Standalone vs. Formatting in Flexible formats

In languages that distinguish between nominative and genitive (or related form such as partitive), the use of symbols in flexible formats also specify the use of nominative forms or genitive (or related) forms of month and day names. 

To understand which pattern characters are used for standalone forms (nominative) versus format forms (genitive or related, such as partitive), see Stand-Alone vs Format Styles, see also the discussion above in Synchronizing Date/Time Names and Patterns.

Supplied vs. Inferred patterns

Some patterns supplied for each skeleton may be extended from the abbreviated form to an inferred full form by developers who use CLDR. 

Some Inferred patterns usage are incorrect, instead use the most closely associated skeletons that are available. Build on a chain of fallback options based on available patterns is a good practice. 

Example expansions:

The correctness of inferred from abbreviated the full will differ by locale. 

In the examples above table, Inferred 2 and Inferred 3 examples are incorrect, because:

Some languages do not use abbreviated months; therefore, a skeleton containing abbreviated month MMM is mapped to a pattern that uses numeric month M or MM. For example, skeleton yMMMd may be supplied with the numeric month d.M.y.

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Day period patterns

There are three pattern characters that can you can use to indicate the day period marker in 12-hour-cycle time formats:

With skeletons (listed in the Code column in Survey Tool) that specify 'h' but no day period, the corresponding patterns are specified with a day period, normally 'a' or 'b'. The patterns can be used to infer how to handle a request for a different day period. For example:

Beginning in CLDR 32, there are 5 additional time patterns that indicate how times should be formatted using day period ranges 'B'. This allows locales to have formats for day period ranges that can display the range symbol in a different position than might be used for symbols for AM, PM, noon, or midnight:

These new patterns are available in Gregorian and Generic calendars, In these new fields, provide locale data by:

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Date-Time Combined Formats

The date-time pattern shows how to combine separate patterns for date (represented by {1}) and time (represented by {0}) into a single pattern. It usually doesn't need to be changed. 

What you want to pay attention to are:

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There are four formats: full, long, medium, and short. Each of these may come in two variants:

Before CLDR 42, there was only one variant for these. In English that variant used the “-atTime” style, as did many other locales. For CLDR 42, that  “-⁠atTime” data has been moved to the “-⁠atTime” variants, and the standard data has initially been extrapolated from the mediu or short formats without literal text. However, it needs to be checked.

The determination of which to use by developers using CLDR data is normally based on the date style, for example:

Following are examples on how the data can be different by locale with different combinations of format length. (note: {1}=date format with {0}= time format)


Another way to look at the example with original patterns and combined result:

Week-Of Patterns

The week-of date patterns were introduced in CLDR 30 for enumerating week count in larger periods, e.g. “week 15 of 2016” or “week 4 of April”. The Survey Tool fields and corresponding English entries are shown below:

For developers who use CLDR data, 

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As described under Date/Time Names, CLDR also provides a relative week period pattern which is used for constructions such as “the week of April 11, 2016”. The English pattern that produces this is “the week of {0}”; the date format that replaces {0} is determined separately. Because the week-of patterns described here may appear in user interfaces that also show dates produced using the relative week period patterns, all of these patterns should be designed with consistent wording and structure.

Flexible - Timezone Append

timezone: {0} {1} 

See in Survey Tool.

The flexible append format for Timezone is used to compose a time and a timezone, to get a result like "11:30 Pacific Time". 

Date/Time Intervals

Interval patterns contain a start pattern and an end pattern (using the Date/Time Symbols). They are used for a range of dates or times, such as "Sept 10–12" (meaning the 10th of September through the 12th of September). The interval format is used where it is necessary to make the pattern as short as possible, and elide information that does not have to be repeated. For example, the pattern used to get "Sept 10–12" in English is "MMM d–d".

Unlike simple Date/Time Patterns, these consist of two parts, typically separated by with some kind of punctuation mark (e.g. English uses en-dash " – "). Also, some fields in the second part are omitted (e.g. "d – d MMM" omits repeat of MMM for the second part). The first field that comes from the second date is marked with red in the examples below.

Interval Formatting

Greatest Difference

Each combination of fields can be used with dates that differ by different amounts. For example, a format for the fields "yMMMd" (year, abbreviated month, and day) could be used with two dates that differ by year, month, or day.

As the examples below indicate, for a given skeleton, each type of difference might need a different pattern.

For example,

Different Calendars 

Date and Time patterns are also available for other calendars in addition to the Gregorian calendar. For example, the Buddhist, Islamic, Hebrew, or Japanese calendars. 

Different calendars work with the data in Gregorian, and Generic in the following ways: