how to determine your target heart rate
Step 2. Start with 220 and subtract your age from it to get an estimate of your maximum heart rate. For example, if you are 25, your maximum heart rate would be 195. Multiply the result by the target heart rate percentage you determined earlier. If you are aiming for 70 percent, you would multiply 195 by 0.7 to get 136.5. If you are aiming for 50 percent, you would multiply 195 by 0.5 to get 97.5. The complete formula is: (220 - Your Age) x Target Heart Rate Percentage = Target Heart Rate.