Maximum Heart Rate: You can calculate your maximum heart rate by subtracting your age from 220. For example, if you're 15 years old, subtract 15 from 220 to get a maximum heart rate of 205. This is the average maximum number of times your heart should beat per minute during exercise.
Calculate your HRR by subtracting your resting heart rate from your maximum rate. Next, multiply your HRR by the minimum and maximum percentage. Multiply your HRR by 0.6; then add your resting heart rate to this number. Multiply your HRR by 0.9; then add your resting heart rate to this number.
Your threshold heart rate will be the average heart rate from a recent intense race or very hard interval from a training ride, where you spent 45-60 minutes in duration at an all-out effort.
In general, your maximum heart rate is about 220 minus your age. Your MHR is the upper limit of what your cardiovascular system can handle during physical activity. For vigorous exercise, aim for a target heart rate of 70 to 85 percent of your maximum heart rate. (I'm not entirely sure how to calculate this one-- check google.)