The Karvonen formula is a method for calculating your target heart rate during exercise based on both your maximum heart rate and your resting heart rate. Unlike simpler approaches that only use your age, the Karvonen formula factors in your current fitness level, making it a more personalized way to set training intensity. It was first introduced by Finnish physiologist Martti Karvonen in a 1957 study on the effects of training on heart rate.
How the Formula Works
The Karvonen formula centers on a concept called heart rate reserve, which is the gap between the fastest your heart can beat and how slowly it beats at rest. That gap represents the usable range your heart has to work with during exercise. The formula multiplies this reserve by a percentage (representing how hard you want to work) and then adds your resting heart rate back in. Written out, it looks like this:
Target Heart Rate = ((Max Heart Rate − Resting Heart Rate) × Intensity%) + Resting Heart Rate
The reason the resting heart rate gets added back at the end is important. Your heart never drops below its resting rate during exercise, so that baseline is always part of the equation. By building upward from your personal resting rate, the formula automatically adjusts for fitness. A well-conditioned person with a resting heart rate of 52 bpm will get a different target than a sedentary person with a resting rate of 78 bpm, even if they’re the same age.
A Step-by-Step Example
Say you’re 40 years old with a resting heart rate of 65 bpm, and you want to exercise at moderate intensity (50% of your reserve).
- Step 1: Estimate your max heart rate. The classic formula is 220 minus your age, so 220 − 40 = 180 bpm.
- Step 2: Find your heart rate reserve. That’s 180 − 65 = 115 bpm.
- Step 3: Multiply by your desired intensity. 115 × 0.50 = 57.5 bpm.
- Step 4: Add your resting heart rate back. 57.5 + 65 = 122.5, so roughly 123 bpm.
To set a training zone rather than a single number, you’d repeat this with two different percentages. For moderate exercise, you might use 50% and 70%, giving you a range of 123 to 146 bpm in this example.
Why It Differs From Simpler Methods
The most basic way to estimate a training zone is to take a flat percentage of your estimated max heart rate. For that same 40-year-old, 50% of 180 is just 90 bpm. But 90 bpm is barely above a resting heart rate for many people and wouldn’t represent meaningful exercise. The Karvonen formula avoids this problem because it works only with the portion of your heart rate that changes during activity, not the portion that’s always ticking along at baseline.
This matters physiologically because heart rate reserve tracks more closely with oxygen consumption, which is the gold standard for measuring exercise intensity. The American College of Sports Medicine treats percentages of heart rate reserve and percentages of oxygen consumption reserve as roughly interchangeable when prescribing exercise intensity. That’s the main reason the Karvonen method became the preferred approach in exercise science and cardiac rehabilitation.
Getting Your Inputs Right
Resting Heart Rate
Accuracy depends on the numbers you plug in. For resting heart rate, measure it while sitting or lying down but fully awake. First thing in the morning, before coffee, is ideal. Place two or three fingers on the inside of your wrist or along the side of your neck and count the pulses for 60 seconds. You can also count for 30 seconds and double it. Do this over several days and average the results, since a single reading can be skewed by stress, caffeine, or a poor night’s sleep.
Maximum Heart Rate
Max heart rate is harder to pin down. The classic 220-minus-age formula, which Karvonen’s original work popularized, is the most widely known estimate. A later analysis by researcher Hirofumi Tanaka proposed 208 minus 0.7 times your age as a slightly more accurate alternative, particularly for older adults. In a study of over 2,000 people aged 12 to 69, both formulas showed the same correlation with actual measured max heart rates (r = 0.72), though both also showed statistically significant differences from measured values. In other words, either formula gets you in the neighborhood, but neither is exact.
For a 40-year-old, the classic formula gives 180 bpm while the Tanaka formula gives 180 as well (208 − 28). The gap widens at older ages. A 60-year-old gets 160 from the classic formula but 166 from the Tanaka version. If precision matters to you, a graded exercise test supervised by a professional will give you a measured max heart rate that no formula can match.
Common Intensity Ranges
The American College of Sports Medicine uses heart rate reserve percentages to define exercise intensity levels. While the exact cutoffs vary slightly across guidelines, the general framework looks like this:
- Light intensity: 30% to 39% of heart rate reserve
- Moderate intensity: 40% to 59% of heart rate reserve
- Vigorous intensity: 60% to 89% of heart rate reserve
Most general health recommendations call for moderate intensity exercise. Using the Karvonen formula at 50% of heart rate reserve is a common starting point for someone building a fitness habit. Athletes training for performance will spend structured time across multiple zones, using higher percentages for interval work and lower ones for recovery sessions.
Where the Formula Falls Short
The Karvonen formula assumes a predictable relationship between heart rate and exertion, and that relationship breaks down in certain situations. The most significant is medication use. Beta-blockers, commonly prescribed for high blood pressure and heart conditions, artificially lower both resting and maximum heart rate. A study of patients on beta-blockers after heart attacks found that the Karvonen formula significantly underestimated the heart rate at which they actually reached meaningful training intensity, by about 11 bpm on average (91 vs. 102 bpm). In 40% of those patients, the gap was large enough to result in undertraining. Researchers concluded that a modified formula was needed for this population.
The formula can also be less reliable for people with irregular heart rhythms, since getting an accurate resting heart rate is difficult when the rhythm varies beat to beat. And because it relies on an age-predicted max heart rate (unless you’ve had yours measured), anyone whose true max deviates significantly from the average for their age will get skewed results. This includes some highly trained athletes whose max heart rates don’t follow typical age-related patterns, as well as people on other medications that affect heart rate.
Putting It Into Practice
Most fitness watches and heart rate monitors let you input a resting heart rate and will calculate Karvonen-based zones automatically. If yours only uses the simpler percentage-of-max method, you can switch to manual zone settings and plug in the numbers yourself using the steps above. Recalculate every few months, since your resting heart rate will drop as your fitness improves, which shifts your training zones upward.
The practical difference between the Karvonen method and simpler calculations is most noticeable at lower intensities and for people who are either very fit or very sedentary. If your resting heart rate is close to the population average of around 70 bpm, the two methods produce fairly similar targets at higher intensities. But if your resting rate is unusually low or high, the Karvonen formula will give you a target that more accurately reflects how hard your body is actually working.