December 12 can fall on any day of the week.
March 12 1977 was a Saturday.
December 12, 1990 was a Wednesday.
December 12 1947 was a Friday.
December 12 1958 was a Friday.
December 12 2010 was a Sunday.
Saturday
December 12, 1972 fell on a Tuesday.
December 12, 1765 fell on a Thursday.
December 12 1979 was on a Wednesday.
December 12, 1991 fell on a Thursday.
December 12, 1933 fell on a Tuesday.