But then it gets weird. As Tyson explains, adding in an extra day every 4 years is kind of overkill. So, to get us back on the right track, we skip leap year once every 100 years, at the turn of the century. But then, that's an over-overcorrection. So to correct the correction, in century years evenly divisible by 400, we add the leap year back in, which is why the year 2000 had a leap day, even though it was a turn of the century year.