It is not nine days until the Ides of March

Despite the title of this MetaFilter post, it is, in fact, ten days until the Ides.

Count it with me: 6, 7, 8, 9, 10, 11, 12, 13, 14, 15. Ten numbers = ten days.

Because the Romans practiced inclusive counting, and also, they always counted backwards rather than numbering the days and going forwards like we do.. The Ides is the Ides, and the day before that is pridie Ides, and the day before that is "three days before the Ides".

Today is pridie Nones.