It's hard for me to keep track. I start a lot more books than I finish. Usually, if I feel like I've gotten what I needed out of a book, I don't feel the need to finish to the end. I also listen to a lot of audio books while driving, and oftentimes don't finish the one I'm listening to before moving on to a new one.

Altogether, i'd estimate that I start at least 20+ books a year... and i'll actually finish only a few of them to the end.