The Karvonen formula is used to calculate your target heart rate during exercise. It factors in both your maximum heart rate and your resting heart rate, giving you a personalized number (in beats per minute) to aim for at any given workout intensity. This makes it more precise than simply taking a percentage of your maximum heart rate, because it accounts for your individual fitness level.
How the Formula Works
The core equation looks like this:
Target Heart Rate = Resting Heart Rate + (Intensity % × Heart Rate Reserve)
Heart rate reserve (HRR) is the difference between your maximum heart rate and your resting heart rate. It represents the working range your heart has available during exercise. The formula takes a percentage of that range based on how hard you want to work, then adds your resting heart rate back in to give you an actual beats-per-minute target.
To break that into individual steps:
- Estimate your max heart rate. The most common method is 220 minus your age. A 50-year-old would get 170 bpm.
- Find your heart rate reserve. Subtract your resting heart rate from your max. If that 50-year-old has a resting heart rate of 65, their reserve is 105 bpm.
- Multiply by your desired intensity. For 75% intensity: 105 × 0.75 = about 79.
- Add your resting heart rate back. 79 + 65 = 144 bpm. That’s the target.
Why Resting Heart Rate Matters
The simpler alternative, just multiplying your max heart rate by an intensity percentage, treats everyone the same age as identical. But two 40-year-olds can have very different fitness levels. One might have a resting heart rate of 55, the other 80. The Karvonen formula captures that difference through heart rate reserve.
The more fit you are, the lower your resting heart rate tends to be, which means your heart rate reserve is larger. You have more “room” between rest and max effort. A less fit person with a high resting heart rate has a smaller reserve, so the same intensity percentage produces a lower target. This is why the American College of Sports Medicine uses heart rate reserve as its preferred method for prescribing exercise intensity.
Measuring Your Resting Heart Rate
Accuracy starts with getting your resting heart rate right. The standard approach is to count your pulse for 60 seconds first thing in the morning, before you get out of bed. For an even more reliable number, do this on three consecutive mornings and average the results. Caffeine, stress, poor sleep, and illness can all temporarily raise your resting rate, so pick mornings that reflect your normal baseline.
Estimating Your Maximum Heart Rate
Most people use the classic formula of 220 minus your age. It was proposed by Fox and colleagues in 1971 and remains the most widely used estimate. A slightly updated version from researcher Hirofumi Tanaka uses 208 minus 0.7 times your age, which produces similar results for most people. Research comparing these formulas found they have similar accuracy when checked against actual maximal heart rate measured on a treadmill test, and the 220-minus-age version may be the best general option because it’s less likely to consistently over- or underestimate.
Both are population-level estimates, though. Individual variation can be significant, sometimes off by 10 to 12 beats in either direction. If your calculated targets feel drastically wrong during workouts (far too easy or impossibly hard), your true max likely differs from the estimate.
Target Zones by Intensity
The ACSM recommends moderate to vigorous aerobic exercise for most adults, defined as 40% to below 90% of heart rate reserve. Here’s how that breaks down in practice:
- Light intensity (30 to 39% HRR): Appropriate for people who are deconditioned or just starting an exercise program. Feels easy, you can hold a full conversation.
- Moderate intensity (40 to 59% HRR): A brisk effort where you can talk but not sing. This is the sweet spot for general cardiovascular health.
- Vigorous intensity (60 to 89% HRR): Harder effort where conversation becomes difficult. Used for improving fitness and performance.
To find your personal range for any zone, just run the Karvonen formula twice, once with the lower percentage and once with the upper percentage. Using the earlier example of a 50-year-old with a resting heart rate of 65 and a heart rate reserve of 105: moderate intensity would span roughly 107 bpm (105 × 0.40 + 65) to 128 bpm (105 × 0.60 + 65).
A Full Worked Example
Say you’re 35 years old with a resting heart rate of 60, and you want to train at moderate intensity (50% to 60% of HRR).
Max heart rate: 220 − 35 = 185 bpm. Heart rate reserve: 185 − 60 = 125 bpm. Lower target: (125 × 0.50) + 60 = 123 bpm. Upper target: (125 × 0.60) + 60 = 135 bpm. Your moderate-intensity zone is 123 to 135 bpm.
Now compare that to someone the same age but with a resting heart rate of 80. Their reserve is only 105 bpm, giving a moderate zone of 133 to 143 bpm. Same age, same intensity percentage, but different targets. That personalization is the whole point of the Karvonen method.
When the Formula Is Less Reliable
The Karvonen formula assumes your resting heart rate is a natural reflection of your fitness. Certain medications change that assumption. Beta-blockers, commonly prescribed for high blood pressure and heart conditions, artificially lower both resting and maximum heart rate. A multicenter study of patients recovering from heart attacks found that the Karvonen formula significantly underestimated appropriate training intensity in people on beta-blockers, producing targets that were too low in about 40% of cases. This can lead to undertraining during cardiac rehabilitation.
The formula also relies on an estimated max heart rate, which introduces error for people at the extremes. Very fit athletes often have true max heart rates above the age-predicted estimate, while older adults or those with cardiovascular conditions may fall below it. If you fall into any of these categories, a supervised exercise test that measures your actual max heart rate will give you far better numbers to work with.
For the general healthy population, though, the Karvonen formula remains one of the most practical tools for dialing in workout intensity without any lab equipment. All you need is your age, a morning pulse count, and a heart rate monitor during exercise.