This is a bit of a rabbit hole. The right way is whatever is agreed, and there are many ways to agree it. https://en.m.wikipedia.org/wiki/Day_count_convention

This is a bit of a rabbit hole. The right way is whatever is agreed, and there are many ways to agree it. https://en.m.wikipedia.org/wiki/Day_count_convention https://en.m.wikipedia.org/wiki/Day_count_convention