Heart-rate zones: training by the numbers

A heart-rate monitor turns vague effort into precise feedback. Used well, zones stop you training too hard on easy days and too easy on hard ones — the two most common mistakes.

What the zones represent

Zones are bands of your maximum heart rate, each driving a different adaptation. The low zones build aerobic base and help recovery; the middle zones improve endurance and stamina; the top zones develop speed and your ability to clear fatigue. No single zone is best — they do different jobs.

Why most training should be easy

The counter-intuitive truth of endurance training is that the majority of it should feel comfortably easy — zones 1 and 2, where you can hold a conversation. This builds the aerobic engine without the fatigue cost of hard efforts, leaving you fresh for the occasional hard session that actually needs to be hard.

Finding your zones

The quick estimate for maximum heart rate is 220 minus your age, then zones are percentages of that. If you know your resting heart rate, the Karvonen method works from your heart-rate reserve — the gap between resting and maximum — and gives more personal zones.

Calculate yours

Enter your age, and optionally your resting rate, into the tool below to get all five zones in beats per minute — then set your watch and train to them.

Why 220 minus age is a rough guide at best

The familiar formula is not a research finding so much as a line drawn through scattered data in the 1970s, and it was never intended as a clinical tool. Measured maximum heart rates for people of the same age routinely vary by twenty beats per minute either side of what it predicts. That spread is wide enough that a zone calculated from it can be a whole zone out for any given individual.

Better-fitting alternatives exist — the Tanaka formula, 208 − (0.7 × age), tracks the data more closely, particularly for older adults, where 220 − age tends to underestimate. But no age-based formula can capture individual variation, because maximum heart rate is largely genetic and barely responds to training. A fit person and an unfit person of the same age often share a maximum; what differs is everything else.

What each zone is actually training

Zone 1 and 2, roughly 50–70% of maximum, build aerobic base. Effort feels easy and conversational, fat is the dominant fuel, and the adaptations — capillary density, mitochondrial volume, stroke volume — are slow to arrive and slow to leave. Most endurance athletes spend the large majority of their training here, which surprises people who assume harder is always better.

Zone 3, around 70–80%, is the moderate middle. It is productive but it is also where undisciplined training collects: hard enough to accumulate fatigue, not hard enough to drive the adaptations that genuinely hard work produces. Zone 4, 80–90%, sits near the lactate threshold and improves the pace you can hold for extended periods. Zone 5, above 90%, develops peak aerobic power and can only be tolerated in short intervals.

The mistake most people make

The common pattern is to train almost everything at moderate intensity — too hard for recovery, too easy for adaptation. The easy sessions creep up in pace because they feel too slow, and the hard sessions drift down because the accumulated fatigue makes true intensity uncomfortable. Everything converges on zone 3 and progress stalls.

The remedy is polarisation: make the easy work genuinely easy, which usually means slower than feels dignified, and reserve real intensity for a small number of sessions. If you can hold a conversation, you are in the right place for a base session. If you can only manage a few words, you are doing interval work whether you planned to or not.

Reserve-based zones and why they differ

Zones can be calculated as straight percentages of maximum heart rate, or by the Karvonen method, which uses heart rate reserve — the gap between resting and maximum. Karvonen accounts for the fact that a fit person with a resting rate of 45 and an unfit person resting at 75 are not doing comparable work at the same absolute heart rate.

The two methods give different numbers for the same person, and Karvonen zones are generally higher. Neither is wrong; they are different definitions. What matters is picking one and staying with it, because comparing a Karvonen zone 2 with a percentage-of-max zone 2 is comparing two different things.

When heart rate is the wrong metric

Heart rate lags effort by a minute or more, which makes it poor for short intervals — the interval is over before your heart rate reflects it. It also drifts upward during long efforts at constant pace, a phenomenon called cardiac drift, so a steady heart rate late in a long session actually represents falling output.

Heat, dehydration, caffeine, illness, altitude and poor sleep all move heart rate independently of how hard you are working. On a hot day your rate at any given pace can be ten beats higher than normal. Treat a zone as a guide that needs interpreting alongside how the effort feels, not a target to chase regardless of conditions.