Can anyone explain why Christmas is on Saturday this year and won't be on Saturday again until eleven years from now (2021) but Christmas will be on Sunday, Tuesday, Wednesday, and Friday twice between now and 2021?

I know about skipping a day every four years because of leap year, but is there a formula? In other words, will Christmas fall on Saturday (or whatever day) in 11 years, then in X years, then in Y years...?

I have a feeling I'm not explaining clearly what I want to know. But feel free to give it a shot.