下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。
CAL_GREGORIAN
(integer)
CAL_JULIAN
(integer)
CAL_JEWISH
(integer)
CAL_FRENCH
(integer)
CAL_NUM_CALS
(integer)
CAL_DOW_DAYNO
(integer)
CAL_DOW_SHORT
(integer)
CAL_DOW_LONG
(integer)
CAL_MONTH_GREGORIAN_SHORT
(integer)
CAL_MONTH_GREGORIAN_LONG
(integer)
CAL_MONTH_JULIAN_SHORT
(integer)
CAL_MONTH_JULIAN_LONG
(integer)
CAL_MONTH_JEWISH
(integer)
CAL_MONTH_FRENCH
(integer)
以下常量自 PHP 4.3.0 起可用：
CAL_EASTER_DEFAULT
(integer)
CAL_EASTER_ROMAN
(integer)
CAL_EASTER_ALWAYS_GREGORIAN
(integer)
CAL_EASTER_ALWAYS_JULIAN
(integer)
以下常量自 PHP 5.0.0 起可用：
CAL_JEWISH_ADD_ALAFIM_GERESH
(integer)
CAL_JEWISH_ADD_ALAFIM
(integer)
CAL_JEWISH_ADD_GERESHAYIM
(integer)