I don't have a percentage, and I don't outright replace items. I just phase in new ones, that will eventually replace favorites that are starting to show wear. Once a piece reaches a certain point of wear, I donate it. If that makes any sense? I guess what I am saying is, I'm not a one-in, one-out person. More of a go-with-the-flow.
This probably equates to about 6-8 replacement pieces a year, that are specifically going to (eventually) take the place of current favorite basics: white and black thin, longsleeve tees, black ponte pants, and currently, a replacement draped black skirt that will eventually take place of my black draped Kamali skirt that is starting to show wear.
Black leather pointy-toed pumps are on my list for replacement this year, and structured shorts in a neutral dark (black or grey), and white.