A healthy exercising heart rate is 50 to 85 percent of the maximum heart rate, which is calculated by subtracting the age from 220, according to the American Heart Association. For a 40-year-old, the maximum heart rate is 180 beats per minute, with the exercise range between 90 and 153.
The heart range for moderate-intensity exercise is 50 to 70 percent of the person's maximum heart rate, notes Mayo Clinic. Vigorous-intensity exercise falls between 70 and 85 percent of the maximum heart rate. To calculate the specific range, the person first finds her maximum heart rate. She multiplies that number by 0.5 to find the low end of the exercising heart rate range. She multiples the maximum heart range by 0.85 to find the upper range.