[kqr]

Year to day is 365 + 1/4 - 1/100 + 1/400 = 365.2425, is it not?

[aravindet]

The 365 + 1/4 - 1/100 + 1/400 is an approximation, not an exact value. The best value* is 365.24217. 46,751 / 128 is actually a better approximation.

https://en.wikipedia.org/wiki/Tropical_year

* This is the ratio of the mean tropical year to the mean solar day; We use means because both the length of the day and the length of the year vary.

The period of rotation (day) of the planet varies due to tidal friction (the moon "drags" oceans against the earth's rotation) and other shifts in mass (e.g. earthquakes) that change the moment of inertia.

https://en.wikipedia.org/wiki/Leap_second#Slowing_rotation_o...

The period of revolution (year) varies mainly due to precession of the equinoxes.

https://en.wikipedia.org/wiki/Axial_precession

[vikingerik]

A Gregorian calendar year is 365.2425 days, yes. A solar year of one equinox/solstice cycle is currently 365.2422 days.