The basic way to calculate your maximum heart rate is to subtract your age from 220. For example, if you're 45 years old, subtract 45 from 220 to get a maximum heart rate of 175. This is the maximum number of times your heart should beat per minute during exercise.
Once you know your maximum heart rate, you can calculate your desired target heart rate zone — the level at which your heart is being exercised and conditioned but not overworked.The American Heart Association and the Centers for Disease Control and Prevention recommend a general target heart rate of:
Moderate exercise intensity: 50 to about 70 percent of your maximum heart rate
Vigorous exercise intensity: 70 to about 85 percent of your maximum heart rate.
Most studies recommends a target heart rate of 65 percent to 75 percent of your maximum heart rate for moderate-intensity exercise.If you're not fit or you're just beginning an exercise program, aim for the lower end of your target zone. Then, gradually build up the intensity. If you're healthy and want a vigorous intensity, opt for the higher end of the zone.