How this calculator works
The predicted maximum heart rate is 220 minus age in this page. The chosen intensity is a percentage range. With the heart rate reserve method, often called Karvonen, the reserve is the maximum minus the resting rate, and the target is the resting rate plus the selected share of that reserve. With the percent of maximum method, the target is simply the percentage of the predicted maximum. Heart rate reserve is lower for the same percentage on most people because it starts from the resting rate.
Formula
Maximum heart rate = 220 - age. Reserve = maximum - resting. Karvonen target = resting + reserve x percentage. Percent-of-maximum target = maximum x percentage.
Worked example
A 35-year-old with a resting rate of 60 has a predicted maximum of 185 and a reserve of 125. The moderate band at 50 to 60 percent of reserve runs from 60 + 125 x 0.50 = 122.5 to 60 + 125 x 0.60 = 135 bpm. The same 50 to 60 percent of maximum would be 92.5 to 111 bpm, which is much lower and sits near resting.
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Frequently asked questions
Which method should I use?
Heart rate reserve is generally more personal because it accounts for your resting rate. Percent of maximum is simpler and appears in many fitness classes. Pick one and keep it consistent.
Why is the percent-of-maximum band so low?
Fifty percent of a maximum of 185 is 92.5 bpm, which can be close to a resting rate. The reserve method adds the resting rate back, so the same percentage maps to a harder effort. This is why the two methods should not be mixed.
Is 220 minus age accurate?
It is a population average with a wide error. If you have a measured maximum from a test or a hard effort, replace the predicted value and recalculate the band.
Should I stay in one zone for the whole session?
Not necessarily. Easy sessions sit in the lower bands, tempo work near the middle, and intervals reach the upper bands. The target is a guide for the main effort, not a rule for every minute.