Summer (Jun–Aug): ~10–30%
Honestly brutal for visibility and more importantly without the snow cap, why even bother. The humidity, clouds, rainy season, you may only glimpse the base. Fuji is for climbing, not viewing in my personal view. So since this is the space for consolation, here is my philosophical take. Think like a Japanese
Uncertainty is where experience is born. If something like Mount Fuji became permanently available and fully predictable, its emotional value would, may or might diminish. Seriously, but I feel Scarcity and uncertainty create anticipation; anticipation creates meaning. May be too much, but if Fuji were permanently hovering outside every train window like a screensaver, people would stop photographing it within two weeks. We, humans adapt absurdly fast, basically emotional compression algorithms with snacks.