My current book I'm working is 20 chapters. The climax as I see it is in Chapter 18, and then there's a mini-extra-climax in Chapter 20.
Mom called me up the other day, and said "Don't drag your book out after the reader is done!" She reads cozy mysteries and she HATES long chapters after the whodunit is revealed.
The early Sherlock Holmes were huge suckers for this. The whodunit would be revealed in the middle and now let's have a whole half a book devoted to their motivation. Great when the motivation was interesting, not when not.