Identify the method before comparing zones
A zone based on 70% of maximum heart rate is not the same as 70% of heart-rate reserve. A watch, coach, and training app can disagree simply because they use different definitions.
The American Heart Association describes age-based maximum-heart-rate estimates and broad target ranges as general guidance, not exact individual limits. The familiar 220 − age estimate can differ from a person’s actual maximum. [1]
Medications and medical conditions can also affect heart-rate responses. A generic zone calculator should not override a clinician’s exercise advice.
Percentage of maximum heart rate
The calculation is:
Target heart rate = estimated or measured maximum heart rate × selected percentage
For a 40-year-old using 220 − 40, the estimated maximum is 180 beats per minute. At 60%, the target is 108 bpm; at 70%, it is 126 bpm.
The arithmetic is exact for the assumed maximum, but the maximum itself is an estimate. That distinction matters more than displaying the boundary to a decimal place.
Heart-rate reserve includes resting heart rate
Heart-rate reserve is maximum heart rate minus resting heart rate. The target calculation is:
Target = resting heart rate + intensity × (maximum heart rate − resting heart rate)
With a maximum of 180 and a resting rate of 60, reserve is 120 bpm. At 60% reserve, the target is 60 + 0.60 × 120, or 132 bpm. That is higher than 60% of maximum, which was 108 bpm.
Do not mix a percentage from one training method with the formula for another. Record the method alongside the result.
Five-zone labels are conventions, not universal clinical categories
Many training systems divide intensity into five zones, but their boundaries and labels vary. A simple percentage-of-maximum scheme might use 50–60%, 60–70%, 70–80%, 80–90%, and 90–100%. That is a coaching convention, not proof that one exact boundary marks a universal physiological threshold.
The percentage bands depend on the estimation method. They do not prescribe time in the upper bands or establish that maximal exercise is appropriate.
An age-estimated maximum is particularly limited for identifying precise physiological thresholds. Formal testing or individualized coaching may use different information.
Use perceived effort and the talk test
The CDC describes a practical talk test: during moderate-intensity activity, talking is generally possible but singing is difficult; during vigorous activity, speaking more than a few words without pausing for breath is difficult. [2]
This adds context when a wearable reading is delayed or inconsistent. Heat, fatigue, hydration, terrain, and training conditions can change the effort associated with a pace or heart rate.
A lower heart rate is not automatically better training, and a higher number is not proof of a more productive session. Match the session to its purpose and recovery needs.
Keep safety separate from performance targets
Stop exercising and seek appropriate help for concerning symptoms such as chest pain, fainting, or severe unexpected breathlessness. Do not try to “complete the zone” despite symptoms.
People with cardiovascular conditions, relevant medications, pregnancy-related considerations, or other medical restrictions should use individualized guidance. A formula-based heart-rate estimate is not a safe upper limit for every person.
For useful tracking, use a consistent resting-rate method, check device fit, and compare similar sessions. A zone is a guide to interpreting effort, not a command to ignore how the body is responding.
Frequently asked questions
Why does my watch show different zones from these formulas?
It may use a different maximum-heart-rate estimate, resting rate, threshold method, or zone convention. Compare the method and inputs before comparing the labels.
Is 220 minus age my true maximum heart rate?
It is a general estimate, not an individual measurement or a guaranteed safe maximum. Actual responses can differ.
Can I use generic zones while taking heart-rate-altering medication?
Use guidance from the treating clinician. Medication can change heart-rate responses, making generic targets inappropriate.
Sources & calculation notes
Primary references are linked below. Dates, limits, and product terms can change; confirm the applicable details before acting.
Use this guide thoughtfully. Educational information, not a diagnosis or individualized medical advice. A screening result or formula cannot establish what is safe or appropriate for a particular person. Consult a qualified healthcare professional for clinical decisions.