This is one of those how long is a piece of string questions. When I was working in commercial kitchens, chopping 25+kg of carrots a day (among other things), I could go for 6 months without needing them to be hit with a stone.But you do need to keep the edge honed, which I don't count as sharpening. If you look at the steel under a microscope after a bit of use, you'll see the micro bevel of the knife start to bend to one side or another. If it's bent too far, you're pushing that bent edge through the food, and it will feel blunt. Swiping that edge along a simple honing rod will straighten that micro bevel, and the knife will cut easily again. If you let it go too long without honing, the edge will bend over completely, and you'll need a stone to correct it. If you're in the area, I also do free sharpening if you bring or post the knife back to me.