Heart rate zones: what they are for and why '220 minus age' fails

Almost every treadmill, chest strap and fitness app builds its zones on the same equation: subtract your age from 220. It is memorable, it is everywhere, and it was never intended to carry this much weight.

Where "220 minus age" came from

The formula was not derived from a controlled study designed to predict maximum heart rate. It emerged from an informal fit to a scatter of existing data in the early 1970s, and it stuck because it is easy to remember.

The consequences are systematic rather than random. It tends to overestimate maximum heart rate in younger adults and underestimate it in older ones. For a 60-year-old the difference against better-validated equations is often eight to ten beats per minute — enough to shift every zone boundary and misclassify what should be an easy session as a hard one.

Better estimates

Tanaka and colleagues published a revised equation in 2001, drawn from a meta-analysis of 351 studies covering more than 18,000 people and cross-validated in a separate laboratory cohort of 514. Their finding was that maximum heart rate falls by about 0.7 beats per year rather than the 1.0 the old formula assumes, and that this holds regardless of sex or training status. Because the two formulas diverge as age rises, the old one increasingly underestimates maximum heart rate in older adults. It is the default our calculator uses. ¹

Gulati and colleagues later derived an equation specifically in women, from 5,437 asymptomatic women undergoing exercise stress testing. They concluded that the traditional male-derived calculation overestimates maximum heart rate for age in women, and argued that sex-specific values belong in clinical practice. ² Our calculator offers it alongside Tanaka when you select female.

One caveat on Gulati worth knowing: it was derived from peak heart rate reached during a symptom-limited stress test, which is not identical to a true physiological maximum, and subsequent work has found it can underestimate peak heart rate in older women.

None of this makes the estimate precise. Individual variation in true maximum heart rate is substantial — roughly ten beats per minute in either direction is normal, and some people sit well outside that. Two people of the same age can genuinely differ by twenty beats.

Maximum heart rate is also not a fitness measure. It does not meaningfully improve with training, and a higher one confers no advantage. It declines with age regardless of how fit you are. If you want a number that reflects conditioning, look at resting heart rate or recovery rate instead.

Why resting heart rate improves the zones

Taking a flat percentage of maximum heart rate ignores the bottom of your range. Two people with the same maximum of 190 but resting rates of 45 and 75 have very different working ranges, and treating them identically produces zones that are too hard for one and too easy for the other.

The Karvonen method uses heart rate reserve — the gap between resting and maximum — and sets zones as percentages of that gap, added back onto resting. Because resting heart rate falls as you get fitter, the zones adjust to your conditioning over time.

Measure resting heart rate on waking, before getting up, ideally averaged over several mornings. A single reading after coffee or a poor night’s sleep is not representative.

What the zones are for

Zone 1 — recovery. Warm-ups, cool-downs, easy movement between hard sessions.

Zone 2 — aerobic base. Conversational pace. This is where most endurance training should live, and it is the zone most recreational athletes skip because it feels too easy to be useful.

Zone 3 — tempo. Comfortably hard, sustainable for thirty to sixty minutes.

Zone 4 — threshold. Hard, close to the point where lactate accumulates faster than it clears.

Zone 5 — VO₂ max. Maximal intervals, sustainable only in short efforts.

The pattern observed across trained endurance athletes is that a large majority of training volume sits at low intensity, with a small proportion at high intensity and relatively little in the middle. The common recreational failure is the opposite: too much moderately hard work, which accumulates fatigue without delivering either the aerobic adaptations of easy volume or the stimulus of genuinely hard intervals.

Zone 2 has become fashionable recently, and the underlying idea is sound — but the fashion has outrun the evidence in places. The core observation is simply that easy volume builds aerobic capacity with low fatigue cost, which has been understood for decades. Claims about precise metabolic thresholds and mandatory durations are considerably shakier than the confident presentation often suggests.

The bottom line

Use Tanaka rather than “220 minus age”, add your resting heart rate so the zones reflect your actual conditioning, and treat the resulting boundaries as approximate — they carry about ten beats of uncertainty inherited from the max-HR estimate.

Then use them mainly to keep your easy sessions genuinely easy. That is the correction most people need, and it matters more than the precise boundary between any two zones.