1. Maximal heart rate:
This number is related to your age. As we grow older, our hearts start to beat a little more slowly. To estimate your maximal heart rate, simply subtract your age from the number 220.
2. Target heart-rate zone:
This is the number of beats per minute (bpm) at which your heart should be beating during aerobic exercise. For most healthy individuals, this range is 50 to 80 percent of your maximal heart rate. So, if your maximal heart rate is 180 bpm, the low end of the range (50 percent) would be 90 bpm, and the high end of the range (80 percent) would be 144 bpm.
What does this recommended heart-rate range mean?
Now that you've determined your target heart-rate zone, you need to know how to put that information to good use. These numbers serve as a guideline - an indicator of how hard you should be exercising.
Those just beginning an aerobic program should probably aim for the low end of the zone and pick up the intensity as they become more comfortable with their workouts. Those who are more fit, or are training for competitive events, may want to aim for the higher end of the zone.
Source : http://www.fitnessconcept.com.my/