[[mapping-date-format]]
=== `format`

In JSON documents, dates are represented as strings. Elasticsearch uses a set
of preconfigured formats to recognize and parse these strings into a long
value representing _milliseconds-since-the-epoch_ in UTC.

Besides the <<built-in-date-formats,built-in formats>>, your own
<<custom-date-formats,custom formats>> can be specified using the familiar
`yyyy/MM/dd` syntax:

[source,console]
--------------------------------------------------
PUT my-index-000001
{
  "mappings": {
    "properties": {
      "date": {
        "type":   "date",
        "format": "yyyy-MM-dd"
      }
    }
  }
}
--------------------------------------------------

Many APIs which support date values also support <<date-math,date math>>
expressions, such as `now-1m/d` -- the current time, minus one month, rounded
down to the nearest day.

[[custom-date-formats]]
==== Custom date formats

Completely customizable date formats are supported. The syntax for these is explained in
https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/time/format/DateTimeFormatter.html[DateTimeFormatter docs].

[[custom-date-format-locales]]
===== Differences in locale information between JDK versions

There can be some differences in date formats between JDK versions and different locales. In particular,
there can be differences in text strings used for textual date formats, and there can be differences
in the results of week-date calculations.

There can be differences in text strings used by the following field specifiers:

* `B`, `E`, `G`, `O`, `a`, `v`, `z` of any length
* `L`, `M`, `Q`, `q`, `c`, `e` of length 3 or greater
* `Z` of length 4

If the text format changes between Elasticsearch or JDK versions, it can cause significant problems
with ingest, output, and re-indexing. It is recommended to always use numerical fields in custom date formats,
which are not affected by locale information.

There can also be differences in week-date calculations using the `Y`, `W`, and `w` field specifiers.
The underlying data used to calculate week-dates can vary depending on the JDK version and locale;
this can cause differences in the calculated week-date for the same calendar dates.
It is recommended that the built-in week-date formats are used, which will always use ISO rules
for calculating week-dates.

In particular, there is a significant change in locale information between JDK releases 22 and 23.
Elasticsearch will use the _COMPAT_ locale database when run on JDK 22 and before,
and will use the _CLDR_ locale database when run on JDK 23 and above. This change can cause significant differences
to the textual date formats accepted by Elasticsearch, and to calculated week-dates. If you are using
affected specifiers, you may need to modify your ingest or output integration code to account
for the differences between these two JDK versions.

[[built-in-date-formats]]
==== Built In Formats

Most of the below formats have a `strict` companion format, which means that
year, month and day parts of the month must use respectively 4, 2 and 2 digits
exactly, potentially prepending zeros. For instance a date like `5/11/1` would
be considered invalid and would need to be rewritten to `2005/11/01` to be
accepted by the date parser.

To use them, you need to prepend `strict_` to the name of the date format, for
instance `strict_date_optional_time` instead of `date_optional_time`.

These strict date formats are especially useful when
<<date-detection,date fields are dynamically mapped>> in order to make sure to
not accidentally map irrelevant strings as dates.

The following tables lists all the defaults ISO formats supported:

`epoch_millis`::

    A formatter for the number of milliseconds since the epoch. Note, that
    this timestamp is subject to the limits of a Java `Long.MIN_VALUE` and
    `Long.MAX_VALUE`.

`epoch_second`::

    A formatter for the number of seconds since the epoch. Note, that this
    timestamp is subject to the limits of a Java `Long.MIN_VALUE` and `Long.
    MAX_VALUE` divided by 1000 (the number of milliseconds in a second).

[[strict-date-time]]`date_optional_time` or `strict_date_optional_time`::

    A generic ISO datetime parser, where the date must include the year at a minimum, and the time
    (separated by `T`), is optional.
    Examples: `yyyy-MM-dd'T'HH:mm:ss.SSSZ` or  `yyyy-MM-dd`.

    NOTE: When using `date_optional_time`, the parsing is lenient and will attempt to parse
    numbers as a year (e.g. `292278994` will be parsed as a year). This can lead to unexpected results
    when paired with a numeric focused format like `epoch_second` and `epoch_millis`.
    It is recommended you use `strict_date_optional_time` when pairing with a numeric focused format.

[[strict-date-time-nanos]]`strict_date_optional_time_nanos`::

    A generic ISO datetime parser, where the date must include the year at a minimum, and the time
    (separated by `T`), is optional. The fraction of a second
    part has a nanosecond resolution.
    Examples: `yyyy-MM-dd'T'HH:mm:ss.SSSSSSZ` or  `yyyy-MM-dd`.

`basic_date`::

    A basic formatter for a full date as four digit year, two digit month of
    year, and two digit day of month: `yyyyMMdd`.

`basic_date_time`::

    A basic formatter that combines a basic date and time, separated by a 'T':
    `yyyyMMdd'T'HHmmss.SSSZ`.

`basic_date_time_no_millis`::

    A basic formatter that combines a basic date and time without millis,
    separated by a 'T': `yyyyMMdd'T'HHmmssZ`.

`basic_ordinal_date`::

    A formatter for a full ordinal date, using a four digit year and three
    digit dayOfYear: `yyyyDDD`.

`basic_ordinal_date_time`::

    A formatter for a full ordinal date and time, using a four digit year and
    three digit dayOfYear: `yyyyDDD'T'HHmmss.SSSZ`.

`basic_ordinal_date_time_no_millis`::

    A formatter for a full ordinal date and time without millis, using a four
    digit year and three digit dayOfYear: `yyyyDDD'T'HHmmssZ`.

`basic_time`::

    A basic formatter for a two digit hour of day, two digit minute of hour,
    two digit second of minute, three digit millis, and time zone offset:
    `HHmmss.SSSZ`.

`basic_time_no_millis`::

    A basic formatter for a two digit hour of day, two digit minute of hour,
    two digit second of minute, and time zone offset: `HHmmssZ`.

`basic_t_time`::

    A basic formatter for a two digit hour of day, two digit minute of hour,
    two digit second of minute, three digit millis, and time zone off set
    prefixed by 'T': `'T'HHmmss.SSSZ`.

`basic_t_time_no_millis`::

    A basic formatter for a two digit hour of day, two digit minute of hour,
    two digit second of minute, and time zone offset prefixed by 'T':
    `'T'HHmmssZ`.

`basic_week_date` or `strict_basic_week_date`::

    A basic formatter for a full date as four digit weekyear, two digit week
    of weekyear, and one digit day of week: `xxxx'W'wwe`.

`basic_week_date_time` or `strict_basic_week_date_time`::

    A basic formatter that combines a basic weekyear date and time, separated
    by a 'T': `xxxx'W'wwe'T'HHmmss.SSSZ`.

`basic_week_date_time_no_millis` or `strict_basic_week_date_time_no_millis`::

    A basic formatter that combines a basic weekyear date and time without
    millis, separated by a 'T': `xxxx'W'wwe'T'HHmmssZ`.

`date` or `strict_date`::

    A formatter for a full date as four digit year, two digit month of year,
    and two digit day of month: `yyyy-MM-dd`.

`date_hour` or `strict_date_hour`::

    A formatter that combines a full date and two digit hour of day:
    `yyyy-MM-dd'T'HH`.

`date_hour_minute` or `strict_date_hour_minute`::

    A formatter that combines a full date, two digit hour of day, and two
    digit minute of hour: `yyyy-MM-dd'T'HH:mm`.

`date_hour_minute_second` or `strict_date_hour_minute_second`::

    A formatter that combines a full date, two digit hour of day, two digit
    minute of hour, and two digit second of minute: `yyyy-MM-dd'T'HH:mm:ss`.

`date_hour_minute_second_fraction` or `strict_date_hour_minute_second_fraction`::

    A formatter that combines a full date, two digit hour of day, two digit
    minute of hour, two digit second of minute, and three digit fraction of
    second: `yyyy-MM-dd'T'HH:mm:ss.SSS`.

`date_hour_minute_second_millis` or `strict_date_hour_minute_second_millis`::

    A formatter that combines a full date, two digit hour of day, two digit
    minute of hour, two digit second of minute, and three digit fraction of
    second: `yyyy-MM-dd'T'HH:mm:ss.SSS`.

`date_time` or `strict_date_time`::

    A formatter that combines a full date and time, separated by a 'T':
    `yyyy-MM-dd'T'HH:mm:ss.SSSZ`.

`date_time_no_millis` or `strict_date_time_no_millis`::

    A formatter that combines a full date and time without millis, separated
    by a 'T': `yyyy-MM-dd'T'HH:mm:ssZ`.

`hour` or `strict_hour`::

    A formatter for a two digit hour of day: `HH`

`hour_minute` or `strict_hour_minute`::

    A formatter for a two digit hour of day and two digit minute of hour:
    `HH:mm`.

`hour_minute_second` or `strict_hour_minute_second`::

    A formatter for a two digit hour of day, two digit minute of hour, and two
    digit second of minute: `HH:mm:ss`.

`hour_minute_second_fraction` or `strict_hour_minute_second_fraction`::

    A formatter for a two digit hour of day, two digit minute of hour, two
    digit second of minute, and three digit fraction of second: `HH:mm:ss.SSS`.

`hour_minute_second_millis` or `strict_hour_minute_second_millis`::

    A formatter for a two digit hour of day, two digit minute of hour, two
    digit second of minute, and three digit fraction of second: `HH:mm:ss.SSS`.

`ordinal_date` or `strict_ordinal_date`::

    A formatter for a full ordinal date, using a four digit year and three
    digit dayOfYear: `yyyy-DDD`.

`ordinal_date_time` or `strict_ordinal_date_time`::

    A formatter for a full ordinal date and time, using a four digit year and
    three digit dayOfYear: `yyyy-DDD'T'HH:mm:ss.SSSZ`.

`ordinal_date_time_no_millis` or `strict_ordinal_date_time_no_millis`::

    A formatter for a full ordinal date and time without millis, using a four
    digit year and three digit dayOfYear: `yyyy-DDD'T'HH:mm:ssZ`.

`time` or `strict_time`::

    A formatter for a two digit hour of day, two digit minute of hour, two
    digit second of minute, three digit fraction of second, and time zone
    offset: `HH:mm:ss.SSSZ`.

`time_no_millis` or `strict_time_no_millis`::

    A formatter for a two digit hour of day, two digit minute of hour, two
    digit second of minute, and time zone offset: `HH:mm:ssZ`.

`t_time` or `strict_t_time`::

    A formatter for a two digit hour of day, two digit minute of hour, two
    digit second of minute, three digit fraction of second, and time zone
    offset prefixed by 'T': `'T'HH:mm:ss.SSSZ`.

`t_time_no_millis` or `strict_t_time_no_millis`::

    A formatter for a two digit hour of day, two digit minute of hour, two
    digit second of minute, and time zone offset prefixed by 'T': `'T'HH:mm:ssZ`.

`week_date` or `strict_week_date`::

    A formatter for a full date as four digit weekyear, two digit week of
    weekyear, and one digit day of week: `YYYY-'W'ww-e`.
    This uses the ISO week-date definition.

`week_date_time` or `strict_week_date_time`::

    A formatter that combines a full weekyear date and time, separated by a
    'T': `YYYY-'W'ww-e'T'HH:mm:ss.SSSZ`.
    This uses the ISO week-date definition.

`week_date_time_no_millis` or `strict_week_date_time_no_millis`::

    A formatter that combines a full weekyear date and time without millis,
    separated by a 'T': `YYYY-'W'ww-e'T'HH:mm:ssZ`.
    This uses the ISO week-date definition.

`weekyear` or `strict_weekyear`::

    A formatter for a four digit weekyear: `YYYY`.
    This uses the ISO week-date definition.

`weekyear_week` or `strict_weekyear_week`::

    A formatter for a four digit weekyear and two digit week of weekyear:
    `YYYY-'W'ww`.
    This uses the ISO week-date definition.

`weekyear_week_day` or `strict_weekyear_week_day`::

    A formatter for a four digit weekyear, two digit week of weekyear, and one
    digit day of week: `YYYY-'W'ww-e`.
    This uses the ISO week-date definition.

`year` or `strict_year`::

    A formatter for a four digit year: `yyyy`.

`year_month` or `strict_year_month`::

    A formatter for a four digit year and two digit month of year: `yyyy-MM`.

`year_month_day` or `strict_year_month_day`::

    A formatter for a four digit year, two digit month of year, and two digit
    day of month: `yyyy-MM-dd`.
