I can't say what fraction of authors or works do this (and I doubt anyone can), and I'm not sure how high it would have to be for the practice to qualify as common. But I'll comment on how an author might write based on their experience without basing a character on themselves, because the question suggests it's not obvious. Here are a few things to consider (note they can be mixed together in practice as well):
* Authors often have polemical intent, and for maximum persuasion they may give a character experiences that would lead a person to the conclusions the author wants readers to adopt, because humans are more liable to change their mind because of that rather than arguments. But the author tweaks any experiences that convinced them of their current view, ensuring they started with a very different view and were the kind of person who'd go on a do-a-180 adventure. This is the "flat character arc", one of three fun story types discussed here.
* The right person from an author's past to make the basis for such a journey may be someone they knew, not themselves. Indeed, they might never have changed their own mind on the issue.
* The right person to adapt into a character might not be whoever changes their mind, but someone whose suffering or exploits make them rethink something. 38
I have a feeling <PERSON>'s works have far more examples of the latter than the former.
* Meanwhile, if the reason to write from one's own experience is not so much persuasion as easy world-building, one might base the characters on those they knew (with properties blended in whatever way serves the story), or do something similar with the plot or setting as well or instead. The ways it can work are endless. You could argue several of <PERSON> stories are based on his experiences in radically different ways.
* Finally, "based on their experiences" is much more open-ended than you might imagine. For example, certain aspects of a person's childhood, adolescence, career etc. might be re-imagined in a sci-fi, fantasy, historical or surreal setting, or a "normal" place that's still not where it happened. Transplanting experiences may require rethinking the people present so much that no author surrogate fits. 460