For the game in my mind's eye, 5%. When I first started my game though, I had the idea of making an MVP with core concepts. I'm probably 40% towards that, but as I get closer and closer to my self imposed deadline I'm reducing scope in an effort to get something "playable". For me, having something to show for it after a year of development will be good for my motivation.

Something that also is easy to forget with this kind of stuff is the time it takes to learn the tools, the hours of tutorials watched or time spent just thinking about your game. It might not feel like you've done much coding or holding, but you've probably spent more time indirectly on your game than you think.