The flag should be displayed on all days, especially:

New Years Day - January 1

Inauguration Day - January 20

Lincoln's Birthday - February 12

Washington's Birthday - third Monday in Febraury

Easter Sunday - (varies)

Mother's Day - Second Sunday in May

Armed Forces Day - Third Saturday in May

Memorial Day - (half-staff until noon) - Last Monday in May

Flag Day - June 14

Independence Day - July 4

Labor Day - First Monday in September

Constitution Day - September 17

Columbus Day - Second Monday in October

Navy Day - October 27

Veteran's Day - November 11

Thanksgiving Day - Fourth Thursday in November

Christmas Day - December 25

and such other days as may be proclaimed by the President of the United States, the birthdays of States (date of admission), and on State holidays.