Never Put Two Spaces After A Period. Period.
Typing two spaces after a period is totally, completely, utterly, and inarguably wrong.
A colleague asked me the other day, “do you always use just one space at the end of the sentence?” She was wondering if there ever was a situation where it was appropriate. We got into talking about American English vs. English, the Oxford comma and the position of a comma inside a quotation mark (American English, regardless of whether it’s logical), and English (where they place it based on logic).
In addition to showing your age (two spaces was the convention as taught when using a typewrite) – the conclusion, is never ever use two spaces after the period. And here is a definitive article as to why, and how single spacing came about.