The easiest way to figure your maximum heart rate is to subtract your age from 220. Once you know this number, you can determine a good heart rate for your next exercise session.
Use heart rate to evaluate whether you are working at an adequate intensity during aerobic activity. For a moderate-intensity workout, aim for a heart rate that is between 50 and 70 percent of your maximum heart rate. For example, if you are 40 years old, your maximum heart rate is about 180 beats per minute. Your moderate-intensity zone is thus between 90 and 126 beats per minute. The Centers for Disease Control and Prevention recommends you fit in at least 150 minutes of activity in this zone every week.
A vigorous-intensity heart rate zone is between 70 and 85 percent of your maximum heart rate. For the 40-year-old example, aim for between 126 and 153 beats per minute. With 75 minutes per week at this intensity level, you meet the CDC's exercise recommendations for health.