Some rogueishly handsome fella over on MacNN.com wrote a review of a OS X utility called WordTarget:

It’s a menubar utility for OS X which simply counts every word. Every time you hit the space bar, that’s another word counted, and that’s fine. No debate there. It does also count hyphens, though, so self-starter is treated as two words, which seems like cheating. To balance that out, however, it does not subtract words when you delete them. Actually, we found that if you highlight some words and delete them all, your word count goes up by one.

That’s probably a bug, and it’s not a significant error: the odd word here or there is not going to make much difference if you’re writing a 170,000-word book, for instance. However, it is significant that it won’t recognize that you’ve deleted whole passages. If you are really doing this to hit a Charlie Brown-like mandated word count, you’ll have to keep this in mind.

But WordTarget is meant for people who are aiming at an ideal number of words rather than a specific commissioned length. Novelists who decide they’re going to write 1,000 words per day no matter what, for instance, they’re the market here. You can presume that WordTarget sales go up every November during NaNoWrMo, where hopeful writers need to hit an average of 1,600 words per day.

Hands On: WordTarget menubar word counter (OS X) – William Gallagher, MacNN (30 December 2014)

Read the full piece because it tells you more, it has screenshots and I worked very hard on it.