One of the most common writing questions people ask me goes something like this... "How long does it take to write a novel?"
The answer to this question isn't simple.
In terms of chronological time, it generally takes me 2-3 years from concept to publication. Of course, during that time I might have 4-5 other projects running in parallel at any given point in time.
A more precise estimate comes from looking at the various stages of a project:
Basic design: 3-4 weeks.
First Draft: 6 weeks.
Subsequent drafts (typically 1-3 of these, depending on how quickly and efficiently things come together. Early novels took quite a few more): 4 weeks per draft.
Editor's review: 4-12 weeks, depending on the editor's workload.
Adding in the editor's notes: 1-2 weeks.
Proofreader's review: 3-8 weeks, again depending on the proofreader's workload.
Adding the proofreader's notes: 1-2 weeks
Final formatting and submission: 1 week.
Total sequential time (as if I could just go from one step to the next without a pause, which isn't how I write) is about 35 weeks. About 8 weeks of the total represents time when I can work on other things (editor or proofreader time). My personal work time is around 27 weeks on each novel, or roughly half a year. I don't work this way, however. I need the breaks between various drafts to mull over elements of the novel's plot and the development of the characters. So in reality, I need more than half a year to get the project completed, even if I don't have any other projects competing for my attention.
I know some authors are able to publish 4 or more novels in a year. To complete four novels, I would have to spend 100% of my available work time on writing. Right now, I spend about 60%. Even with 100% time utilization, I'd still need some significant efficiency improvements to get to a total of 4 novels in a year.
I don't plan on doing that. Part of what appeals to me with writing is the flexibility I have to work when I want, and do other things when they become a priority. I wouldn't give that up to increase production.
My current pace will have me releasing about two novels a year. Some years (like 2013), I'll only manage one title. Some years, I'll get three out. There are plenty of projects in the pipeline to sustain this release rate for 2-3 years ahead.