The starting point — estimated maximum heart rate
The standard, widely used estimate for maximum heart rate is 220 minus your age — a simple population-average formula, not a measurement of your actual physiological max (which varies meaningfully between individuals of the same age and can only be measured precisely via a supervised maximal exercise test). Every zone in this model is calculated as a percentage of this estimated number.
The five zones
Zone 1 (50-60% of max HR): very light activity, easy recovery pace. Zone 2 (60-70%): light aerobic activity, commonly recommended for building an aerobic base and burning fat as the primary fuel source. Zone 3 (70-80%): moderate aerobic activity, improving cardiovascular efficiency. Zone 4 (80-90%): hard anaerobic-threshold effort, improving speed and lactate tolerance. Zone 5 (90-100%): maximum effort, sustainable only for very short durations.
A worked example
For a 30-year-old, estimated max heart rate = 220 − 30 = 190 bpm. The five zones work out to: Zone 1, 95-114 bpm. Zone 2, 114-133 bpm. Zone 3, 133-152 bpm. Zone 4, 152-171 bpm. Zone 5, 171-190 bpm. A 30-year-old aiming for an easy aerobic-base run would target roughly 114-133 bpm (Zone 2); a hard interval session might push into 152-171 bpm (Zone 4).
Why this is a starting estimate, not a precise measurement
The 220-minus-age formula is a population average with meaningful individual variation — two people of the identical age can have genuinely different true maximum heart rates. It's a reasonable, widely used starting point for structuring training intensity, but athletes seeking precision typically get their max heart rate measured directly via a supervised test, or refine their zones using the Karvonen method (covered in a companion article), which factors in resting heart rate as well.
Why zones matter for training design
Different training goals call for different zone emphasis — building aerobic endurance favors more time in Zones 2-3, while improving top-end speed and lactate tolerance calls for structured Zone 4-5 work. Training almost exclusively in one zone (a common mistake for beginners, who often default to a moderately hard "Zone 3-ish" pace for every session) tends to produce slower overall improvement than a deliberately varied mix across zones.