To estimate target heart rate, calculate the maximum heart rate (the heart rate estimated to correspond to the rate of maximum oxygen use), which is 220 minus age. Target heart rate during moderate intensity activities is about 50 to 70% of maximum heart rate (multiply maximum heart rate by 0.5 and 0.7, respectively). Target heart rate during vigorous physical activity is about 70 to 85% of maximum heart rate (multiply maximum heart rate by 0.7 and 0.85, respectively).