Heart-rate reserve is the difference between maximum heart rate and resting heart rate. The Karvonen method uses that reserve to create training targets, then adds resting heart rate back in.
The calculation is:
Target heart rate = resting heart rate + intensity × (maximum heart rate − resting heart rate)
If resting heart rate is 60, maximum heart rate is 180, and the selected intensity is 60%, heart-rate reserve is 120. The target is 60 + 0.60 × 120 = 132 beats per minute.
Why include resting heart rate?
Two people can have the same maximum but different resting rates. Heart-rate reserve describes the usable span between those points. It is one of several relative-intensity methods discussed in a 2022 cardiorespiratory-fitness practice statement, alongside oxygen-uptake reserve and perceived exertion.
The method is often described as more individualized than using a percentage of maximum alone. That does not mean it precisely identifies a physiological threshold for every person.
The result depends on two uncertain inputs
Resting heart rate should be measured under calm, repeatable conditions. Illness, sleep, stress, medication, caffeine, temperature, hydration, and device quality can shift it.
Maximum heart rate is frequently estimated. The Tanaka study supports 208 − 0.7 × age as a group-level prediction, but individual maximums vary widely around any age equation. An error in estimated maximum flows directly into every reserve-based zone.
Use a measured maximum only when it came from a reliable, appropriate test. Do not perform unsupervised maximal exertion simply to improve a calculator input.
How to use heart-rate reserve responsibly
Label the maximum as measured or estimated and save the resting-rate conditions. Treat calculated boundaries as approximate. Pair them with breathing, the talk test, and perceived exertion. On a hot day, during illness, or after poor sleep, the same heart rate may feel very different.
Medication and health conditions can change the heart-rate response, so a generic formula may be unsuitable. A qualified professional can help set an individualized range when that context matters.
The current public calculator uses percentages of measured or age-estimated maximum rather than heart-rate reserve, so it does not pretend a resting value was collected when it was not. Explore the heart-rate calculator, learn to measure resting heart rate, or examine maximum-heart-rate estimation.