What is the Karvonen formula?
The Karvonen formula is a method for estimating a target heart rate during exercise that accounts for an individual's resting heart rate. Unlike simpler formulas that rely on age alone, the Karvonen approach incorporates resting heart rate to produce a more personalized estimate. It is widely used in exercise physiology and cardiac rehabilitation settings to help guide aerobic training intensity.
The formula was developed by the Finnish physiologist Martti Karvonen and colleagues in the 1950s. The core idea is that the heart rate reserve — the difference between maximum heart rate and resting heart rate — represents the physiological capacity available for exertion. By calculating a percentage of this reserve and adding back the resting heart rate, the formula yields a target that reflects an individual's cardiovascular fitness level more accurately than age-based tables alone.
How the Karvonen formula works
The calculation proceeds in three straightforward steps. First, estimate maximum heart rate using the traditional formula:
Maximum heart rate = 220 − age
Second, determine the heart rate reserve:
Heart rate reserve = maximum heart rate − resting heart rate
Third, calculate the target heart rate for the desired intensity:
Target heart rate = (heart rate reserve × intensity percentage) + resting heart rate
The result is rounded to the nearest whole number. This estimate accommodates ages from 5 to 120 years, intensity percentages from 0 to 100, and resting heart rates of 20 beats per minute and above, provided the resting value remains below the estimated maximum.
The resting heart rate should be measured under consistent conditions — ideally first thing in the morning, before getting out of bed, over a full minute. A lower resting heart rate generally reflects greater cardiovascular efficiency and will shift the target exercise heart rate accordingly.
Why resting heart rate matters
Including resting heart rate is what distinguishes the Karvonen formula from a simple percentage-of-maximum approach. Two people of the same age can have markedly different resting heart rates — a trained endurance athlete might have a resting rate of 45 beats per minute, while a sedentary person of the same age might measure 75. If both aim for 70% intensity, a formula that ignores resting heart rate would give them identical targets, despite their different cardiovascular baselines.
The Karvonen formula adjusts for this. The athlete's lower resting rate expands the heart rate reserve, resulting in a higher absolute target that better reflects their training capacity. Conversely, the higher resting rate of the less-conditioned individual produces a narrower reserve and a comparatively lower target. This adjustment makes the estimate more responsive to fitness level.
Worked example
Consider a 40-year-old with a resting heart rate of 60 beats per minute who wants to exercise at 70% intensity.
Step one — estimate the maximum heart rate:
220 − 40 = 180 bpm
Step two — calculate the heart rate reserve:
180 − 60 = 120 bpm
Step three — apply the intensity percentage and add the resting heart rate:
(120 × 0.70) + 60 = 84 + 60 = 144 bpm
The estimated target heart rate for this individual exercising at 70% intensity is 144 beats per minute. This is the rate the person would aim to maintain during steady-state aerobic exercise to work within the prescribed zone.
How to interpret the estimate
A target heart rate derived from the Karvonen formula is an estimate — a numerical guide to help structure exercise intensity, not a precise physiological prescription. It can be used to define training zones: moderate-intensity exercise typically falls in the 50% to 70% range, while vigorous-intensity exercise occupies the 70% to 85% range.
Interpreting the result involves comparing the estimated target against how the body actually feels during exertion. The rating of perceived exertion, or the talk test, can serve as a practical cross-check. An individual who can comfortably hold a conversation while exercising near the estimated target is likely working at a moderate intensity. If speaking becomes difficult, intensity may be higher than intended.
The estimate is not a diagnosis, medical advice, or a substitute for professional treatment. It should not be used to disregard symptoms such as dizziness, chest pain, or unusual shortness of breath during exercise. Anyone with a known cardiovascular condition, or anyone beginning a new exercise program after a period of inactivity, should consult a qualified healthcare professional before using heart rate targets to guide training.
Factors that influence the estimate
Several variables can affect the reliability of the Karvonen estimate. The maximum heart rate formula of 220 minus age is a population-level average and does not account for individual variation — actual maximum heart rates can differ by 10 to 15 beats per minute or more in either direction. Genetics, body size, altitude, and training history all play a role.
Medications are another important consideration. Beta-blockers, calcium channel blockers, and certain other cardiovascular drugs can blunt the heart rate response to exercise, rendering formula-based targets inaccurate. Anyone taking such medications should discuss exercise heart rate goals with their prescribing clinician rather than relying on a formula alone.
Hydration status, ambient temperature, caffeine intake, and emotional stress can also temporarily alter heart rate during exercise. These factors mean that a target calculated on paper may not align perfectly with real-world readings on any given day.
Accuracy and limitations
The Karvonen formula provides a more individualized estimate than age-only methods, but it has inherent limitations. The underlying maximum heart rate estimate is imprecise for many individuals, and any error in that figure propagates through the entire calculation. The formula also assumes a linear relationship between heart rate and oxygen consumption, which holds reasonably well for most people during submaximal aerobic exercise but becomes less reliable at very low or very high intensities.
The estimate should be treated as a starting point rather than a definitive target. Adjusting intensity based on perceived exertion, breathing patterns, and overall well-being is essential. The formula is not suitable for diagnosing any medical condition, prescribing treatment, or guiding exercise in clinical populations without professional oversight.
Practical applications in exercise planning
Despite its limitations, the Karvonen formula remains a useful tool for structuring aerobic training. It can help individuals establish heart rate zones for warm-up, fat-burning, endurance, and high-intensity intervals. Fitness professionals often use it to design progressive programs where intensity increases gradually over weeks or months.
For those using heart rate monitors or fitness wearables, the Karvonen-derived target can be entered as a custom zone, allowing the device to provide real-time feedback during workouts. This combination of an estimated target and objective monitoring can support more consistent and purposeful training sessions.
Sources
- American Heart Association, "Target Heart Rates Chart," https://www.heart.org/en/healthy-living/exercise-and-physical-activity/fitness-basics/target-heart-rates
- Karvonen, J., & Vuorimaa, T. (1988). Heart rate and exercise intensity during sports activities: Practical application. Sports Medicine, 5(5), 303–311. https://doi.org/10.7600/jspfsm1949.37.245
Editorial record
This article was drafted by the SoupCalc Editorial Team to provide a clear explanation of the Karvonen formula, its calculation steps, and its role in estimating exercise heart rate targets. All source references were current as of the date of review. No automated generation tool produced the final text, and the content has not been reviewed by a licensed clinician. Readers are encouraged to discuss exercise plans with a qualified healthcare provider. Author: SoupCalc Editorial Team Last reviewed: August 11, 2026.