To determine your ideal running heart rate, first you’ll need to calculate your maximum heart rate. To calculate your maximum heart rate, subtract your age from 220. For example, if you’re 40 years old, your maximum heart rate would be 180. Your maximum heart rate may vary 15 to 20 beats per minute in either direction. The American Heart Association recommends exercising with a target heart rate of your maximum heart rate of 50 to 75% for beginners, and for moderately intense exercise. You can work at 70 to 85% of your maximum heart rate during vigorous activity.