karvonen formula: This method of calculating your target training zone is based on your maximal heartrate and resting pulse. The Karvonen Method is one of the most accurate ways to calculate your target heart rate. It uses a mathematical formula that takes your age, gender and resting heart. The Target Heart Rate ( THR ). (RHR), then the results are calculated using the Karvonen method . Otherwise a standard calculation based on age is used. The Karvonen Heart Rate Formula This formula is one of the most effective methods used to calculate your target heart rate for aerobic (cardio) exercise.