Chicago Manual of Style 16 (books) and AP Stylebook 2016 (media) agree unless noted.
Chicago style dictionary is Merriam Webster’s Collegiate Dictionary, Eleventh Edition (MW11)
AP style dictionary is Webster’s New World Collegiate Dictionary, Fifth Edition (WNW5)
Christmas, Christmas Day—(never
Xmas). Also Christmas Eve, Christmastime, Christmas tree. Note that happy holidays, seasons greetings, and merry Christmas are all lowercased (except for the word Christmas).
daylight saving time—(lowercase, no s on saving) begins 2 a.m. on the second Sunday of March, and ends at 2 a.m. the first Sunday of November (except in areas that exempt themselves). Also, it’s daylight time, but Eastern Daylight Time.
Columbus Day—Oct. 12, but the federal legal holiday is the second Monday in October.
D-Day (AP Style) D-day (Chicago Style)—June 6, 1944
Easter—date varies from year to year
Election Day, election night—first Tuesday after the first Monday in November
Father’s Day—third Sunday in June
Hanukkah—usually occurs in December but sometimes falls in late November
Inauguration Day—only capitalize when referring to inauguration events for a U.S. president.
Independence Day, Fourth of July, July Fourth—All acceptable when referring to the holiday. If you are just referring to the date, use the regular date format. July 4 was the last time she visited a casino.) NOTE: CMS also includes “the Fourth” as acceptable.
Labor Day—first Monday in September
Martin Luther King Jr. Day—third Monday in January. His actual birth date was Jan. 15, 1929.
May Day—May 1 (not mayday, which is an international distress signal)
Memorial Day—last Monday in May
Mother’s Day—second Sunday in May
New Year’s Day, New Year’s Eve. AP also specifies New Year’s and Happy New Year.
Saint Patrick’s Day
Sept. 11 (AP Style) September 11 (Chicago Style) —and both agree 9/11 is also acceptable when referring to the September 11, 2001 terrorist attacks.
Thanksgiving, Thanksgiving Day—fourth Thursday in November
Presidents Day (AP Style) Presidents’ Day (Chicago Style)—unofficial name
or Washington’s Birthday—official name
The formal name and official federal government name for the holiday is Washington’s Birthday, but many, including many governmental entities, use the term Presidents Day.
President George Washington’s birthday is computed as Feb. 22, but the federal legal holiday is the third Monday in February.
AP notes that the lack of apostrophe in Presidents Day is an exception to their usual dictionary, Webster’s New World College Dictionary, who spells it Presidents’ Day.
Thanksgiving—fourth Thursday in November
Valentine’s Day—(with Valentine Day as a secondary variant in MW11)
Veterans Day—Nov. 11, in commemoration of the day WWI ended in 1918, and for the end of hostilities in 1945. Observed as a legal holiday in the U.S. to honor the veterans of the armed forces.