You take your heart rate max and subtract your resting pulse.Then you use this to calculate the desired percentage.And then you add your resting pulse again. eg: rest = 45, max = 200. we're gonna calc your 60% zone.... 200-45 = 155(this is your working pulse) 155x0.6=93 93+45(resting pulse)=138 this is how I learned to calculate it. Hope it makes sense?