It is really just different for each blade and each face. I will use one until it either tugs noticeably or it just wont cut anymore. I dont really count. Of course, im sure that the number of passes, soaps, and razor have something to do with it as well. Bottom line is, just switch blades when you feel it's time.
I have changed after one shave, and I have used one blade for 19 days. Now, I change after a week unless the blade starts to tug. Glad you found us.
