Get the current day name:

The day of the week for a particular date:

The day of the week today:

Hours, minutes, and seconds do not affect the day of the week:

The 400-year cycle of the Gregorian calendar includes an integral number of weeks:

There are 20871 weeks in those 400 years because there are 97 leap days in the cycle:

A century never begins on a Sunday:

No matter how the beginning of a century is defined:

Conway's Doomsday rule observes that certain dates within a Gregorian calendar year will always fall on the same day of the week, including the last day of February, the 4th day of the 4th month, the 6th day of the 6th month, and others:

Conway calls this the doomsday of the year, which is Tuesday for 2017:

Thursday, October 4 in the Julian calendar was followed by Friday, October 15 in the Gregorian calendar:

This computes the number of times each day of the week occurs as a 13th of the month over the complete 400-year cycle of the Western (Gregorian) calendar:

The 13th of the month falls more often on a Friday than on any other day of the week: