Heart-rate zones divide an exercise heart-rate range into bands. A five-zone chart can make intensity easier to plan, but the crisp boundaries are estimates—not switches that change your physiology at one beat per minute.
Where the zones come from
The simplest method estimates maximum heart rate from age, then multiplies it by percentages. Fitness Age Calculator uses the Tanaka equation when a measured maximum is unavailable and displays five practical bands from 50% to 100% of that maximum.
The American Heart Association’s public guidance describes about 50–70% of maximum as moderate intensity and about 70–85% as vigorous intensity for general use. Its chart also says age-derived figures are averages.
Another approach uses heart-rate reserve: measured or estimated maximum minus resting heart rate, with the resting value added back after applying an intensity percentage. A clinical practice statement discusses heart-rate reserve, oxygen-uptake reserve, and perceived exertion among several ways to set exercise intensity.
Why your zones may not match a friend’s
Two people of the same age can have different measured maximum and resting heart rates. Fitness, medication, heat, altitude, illness, dehydration, sensor accuracy, and activity type can change the heart-rate response. Beta blockers and other medicines can make generic percentage charts especially unsuitable.
Device makers may also use different zone counts, formulas, or thresholds. Changing a watch setting can redraw your history without any change in your body.
Pair the number with how exercise feels
Use breathing and speech as a cross-check. At moderate intensity, you can generally talk but not sing. At vigorous intensity, only a few words may be comfortable before a breath. If a calculated zone says “easy” while the effort feels unusually hard, the body’s signal matters more than the chart.
Start near the lower end if you are new to structured exercise. Stop for chest pain, faintness, severe breathlessness, or another alarming symptom, and use appropriate emergency help for severe or sudden symptoms.
Read boundaries as ranges
A heart rate of 139 is not meaningfully different from 140 just because a table changes color. Look for steady patterns across a session and comparable sessions. Record whether maximum heart rate was measured or estimated.
Create your bands with the heart-rate zone calculator, understand the maximum-heart-rate estimate, and learn the equipment-free talk test.