Forget the formulae, it's useless because of the +/-20% variations that can be observed. The only real way to find max-HR is to do it experimentally. There's a running and biking-test and most people find they can hit it a little higher on the biking. If you don't want to do an actual lab test, at least verify your max-HR reading with two HRMs to verify that they're pretty close to each other. Your real max-HR is probably around 200-205, forget the 188...