When running, your heart rate should be between 50% to 85% of your maximum heart rate. To calculate your maximum heart rate, subtract your age from 220. For example, if you are 40 years old, your maximum heart rate would be 180 beats per minute. Most runners between ages 20 to 45 will want to stay between 100 and 160 beats per minute (bpm), on average. However, the ideal heart rate while running is different for each person and depends on factors such as age, weight, fitness level, and family history. To determine your target heart rate range, you can use a formula based on your age and maximum heart rate.

If your heart rate dips below 50% of your maximum heart rate, you might want to pick up the pace to get better results from your workout. If your heart rate reaches its maximum, you might want to back off to be able to finish your run. A heart rate monitor can help you keep track of your heart rate while running.

Its important to note that there is no "normal" heart rate when running, as each person is different and their heart rate can be affected by various factors such as age, weight, fitness level, and family history. Additionally, other variables can influence your heart rate when running, such as routine stress and anxiety, other medical conditions, certain medications, and higher ambient temperature and humidity.

In summary, your heart rate while running should be between 50% to 85% of your maximum heart rate, which can be calculated by subtracting your age from 220. Most runners between ages 20 to 45 will want to stay between 100 and 160 beats per minute (bpm), on average. However, the ideal heart rate while running is different for each person and depends on various factors. A heart rate monitor can help you keep track of your heart rate while running.