Not counting books I give up on: On average, maybe five. In a good year, maybe 10. In a rare year, maybe 20.
The mental circuits I use for reading aren't much different than those I use for coding, at least when it's non-fiction, so it tends to be one or the other. I also can really only do one thing at a time. I find it super unsatisfying to not absolutely gorge on one thing. Even with exercise, I prefer something that's compatible with not thinking about the exercise so I can think about whatever I'm gorging on.
... I should be reading more fiction at least.