Target In On Your Cardio...To estimate your target heart rate range when doing cardio, simply start with the number 220 and subtract your age. So a person who is 50 years old would take 220 - 50 which is 170. That means that 170 is their maximum expected heart rate while doing aerobic exercise. Then take 40 off that number, 170 - 40, which is 130. So the target heart rate range for a 50 year old individual is 130 to 170 while doing aerobic exercise in order to maximize fat burning. Of course certain health conditions could affect those numbers so check with your doctor if you are not sure. Also remember to work up to more intense exercise if you are just starting out.