December 2018 calendar is nearly full of half-staff flags due to the rule that U.S. flags should fly at half-staff for 30 days following the death of a U.S. President. Ex-President George H.W. Bush passed away on November 30th, 2018. The first day the flags would be flown at half-staff would be the next day, which would be December 1st. Only December 31st does not have a half-staff flag. December 7th is Pearl Harbor Day. Since 1994, flags are flown at half-staff on December 7th.