Heart rate reserve (HRR) is a method for determining an aerobic intensity zone. The formula below is used to determine the target zone of 60-85%:

• Estimate your own maximal heart rate (MHR) = 220 minus age (220 – age)
• Resting Heart Rate (RHR) = Choose a time when you are relaxed such as immediately after waking up from sleep. Using your index and middle fingers, find your carotid or radial pulse. Take this for 30 seconds and multiple times 2 for a value in beats per minutes.
• Heart Rate Reserve (HRR) = MHR – RHR
• Training Intensities (TI) = HRR x TI + RHR. The optimum aerobic training zone is found between the 60% and 85% training intensities. Older adults or individuals who have been physically inactive should start at 40% to 50% training intensity during the first few weeks of the exercise program. The zone should be recalculated periodically because values will change as fitness changes.

60 Percent TI = HRR X .60 + RHR = ___ bpm
85 Percent TI = HRR X .85 + RHR = ___ bpm

Note that percentages lower than 60 may be advisable for individuals new to working out, but 60-85% HRR is a good target range for most people after a few weeks of regular aerobic training. 

Calculating the HRR formula quickly with Google

The heart rate reserve calculation formula can be entered in a google search box as follows (replacing your age for "AGE" and your resting heart rate for "RHR" in the formula):

(((220-AGE)-RHR)*.85)+RHR

&

(((220-AGE)-RHR)*.60)+RHR