I usually lose count around 30, and just keep using it until I feel a bit of irritation. Haven't really made an effort to keep track beyond that, but I probably should.
30! I read people talking about this kind of thing and I just can't fathom it. I really like some vintage blades. In fact, I've used a Spoiler for the last 2 days. With most blades I get 3 good shaves and I can push it to a 4th or even 5th but the quality of the shave is not as good on these last couple. With a Spoiler, I get 5 good shaves and can push it to 6 but the 6th will be fairly irritating. Going to 7 is a bad idea. I tried pushing a vintage British Gillette Super Silver to 8 shaves last week and I had to stop mid shave on the 8th shave and put a fresh blade in. I love the vintage blades and do get a couple more shaves out of them than I get out of a modern blade but I couldn't get 10 let alone 30.