The PHP checkdate() function is used to check if a Gregorian date is valid.

The PHP date() function formats a local date and time, and returns the formatted date string.

The PHP date_add() function adds a specified number of days, months, years, hours, minutes, and seconds to a date.

The PHP date_create() function returns a new DateTime object.

The PHP date_create_from_format() function returns a new DateTime object formatted according to the specified format.

The PHP date_date_set() function sets a new date.

The PHP date_default_timezone_get() function returns the default timezone used by all date/time functions in the script.

The PHP date_default_timezone_set() function sets the default timezone used by all date/time functions in the script.

The PHP date_diff() function returns the difference between two DateTime objects.

The PHP date_format() function returns a date formatted according to the specified format.

The PHP date_get_last_errors() function returns the warnings/errors found while parsing a date string.

The PHP date_interval_create_from_date_string() function sets up a DateInterval from the relative parts of the string.

The PHP date_interval_format() function is an alias of DateInterval::format().

The PHP date_isodate_set() function sets a date according to the ISO 8601 standard, using weeks and day offsets (instead of using a specific date).

The PHP date_modify() function modifies the timestamp.

The PHP date_offset_get() function returns the timezone offset.

The PHP date_parse_from_format() function returns an associative array with detailed information about a specified date, using to the specified format.

The PHP date_parse() function returns an associative array with detailed information about a specified date.

The PHP date_sub() function subtracts some days, months, years, hours, minutes, and seconds from a date.

The PHP date_sun_info() function returns an array containing information about sunset/sunrise and twilight begin/end, for a specified day and location.