Why is 2017 not considered to be a leap year when it starts 2 weekdays later than 2016 - thus skipping a day?

Answer 1

2016 is a leap year therefore the following year (2017) starts one day later than it normally would had 2016 been a common year. In other words, 2016 contains the "leap day" (February 29th), not 2017. Thus every date from March 1st 2016 onwards is one day later than it normally would have been.

Note that a common year has 365 days, which is exactly 52 weeks plus 1 day. Therefore consecutive common years will always advance by one day, as will any leap year that follows them. But the year immediately after a leap year always advances by 2 days because the leap year includes a leap day.

Leap years occur on all years divisible by 4 unless the year is also divisible by 100 but not by 400. Thus 2017 will be a common year (not divisible by 4) while 2016 will be a leap year (divisible by 4 but not by 100). 1900 was a common year (divisible by 4 and 100, but not by 400) while 2000 was a leap year (divisible by 4, 100 and 400).