Heart Rate Reserve Calculator (Karvonen)
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/9/2026
The Karvonen method calculates the target heart rate with target HR = ((max HR − resting HR) × intensity) + resting HR. For a 30-year-old with a resting HR of 60 bpm and an intensity of 50 to 85%, the target zone runs from about 124 to 168 bpm.
Explanation
The Karvonen method, developed by Finnish physiologist Martti Karvonen, calculates a target heart rate zone that accounts not only for maximum heart rate, but also for resting heart rate — unlike a simple percentage of max HR, which ignores this individual parameter and instead tracks recovery in a different way, the way our heart rate recovery calculator measures how quickly heart rate drops after exertion. The principle rests on heart rate reserve (HR reserve = max HR − resting HR), which represents the heart's actual working range between its resting state and maximum effort. This reserve is then multiplied by the targeted intensity percentage, and the resting HR is added back: it's this last addition that distinguishes Karvonen from a direct percentage of max HR, and explains why the two methods give different results for the same profile. A well-trained person with a low resting HR (a sign of better cardiovascular fitness) therefore gets slightly different target zones than a less trained person of the same age, which makes this method more personalized. Max HR here is estimated with the Tanaka formula (208 − 0.7 × age), the same one used on our target heart rate calculator, to keep results consistent from one calculator to another.
Example: 30 years old, resting HR 60 bpm, 50-85% zone
Inputs
Age: 30. Resting HR: 60 bpm. Target intensity: 50% to 85%.
Calculation
Max HR ≈ 208 − 0.7×30 = 187 bpm. HR reserve = 187 − 60 = 127 bpm. Min target HR = 127×0.50 + 60 = 123.5 bpm. Max target HR = 127×0.85 + 60 ≈ 167.95 bpm.
Result
The target zone for this profile runs from about 124 to 168 beats per minute.
Frequently asked questions
Why measure resting HR upon waking?
Resting heart rate is at its lowest and most stable right after waking up, before getting up and before any stimulation (coffee, stress, activity): it's the most reliable and reproducible measurement from one day to the next. A measurement taken during the day is generally higher and less representative of the true resting state.
Why is the Karvonen method considered more precise than a direct percentage of max HR?
Because it factors in individual fitness via resting HR: at the same max HR, two people of equal age but different training levels get different target zones with Karvonen, whereas a simple percentage of max HR would give exactly the same bounds for both, with no distinction.
Should you use Karvonen or a direct percentage of max HR?
Both methods are widely used and give broadly consistent results; Karvonen is often preferred by trained athletes looking for a more personalized zone, while a direct percentage of max HR remains simpler to remember. Either way, these formulas remain estimates: an actual max HR measurement (a supervised stress test) gives a more reliable result than an age-based estimate.