Heart Rate Zone Calculator

How your zones are calculated

Heart rate zones are built in two steps: estimate the fastest your heart can beat, then divide the range below that ceiling into five bands. Almost all of the uncertainty lives in the first step, and almost all of the training decisions get made in the second.

Step one: maximum heart rate

Maximum heart rate is the highest rate your heart reaches at all-out effort. It falls steadily with age, it is largely independent of fitness, and training does not raise it. A fitter version of you pushes more blood per beat, but the ceiling on the beats themselves stays where it was. This calculator predicts it with the Tanaka equation.

Step two: the five bands

If you leave the resting heart rate field empty, each zone boundary is a plain percentage of that maximum. For our 40-year-old, zone 2 runs from 60 to 70 per cent of 180 bpm.

That method has a blind spot: it ignores the bottom of your range. Your heart does not idle at zero, it idles at your resting rate, and the working range available to you is the distance between resting and maximum. Karvonen, Kentala and Mustala formalised that distance in 1957 and called it heart rate reserve. Percentages are then taken of the reserve and added back onto the resting rate.

Notice how far apart those two answers are. For the same person on the same day, percentage of maximum puts zone 2 at 108–126 bpm while Karvonen puts it at 132–144 bpm. That is not a rounding difference; it is the gap between a brisk walk and a steady run. Karvonen is generally the better guide, and the advantage grows the lower your resting rate goes, because percentage of heart rate reserve tracks percentage of oxygen uptake reserve more closely than percentage of maximum does. This is why the resting field is on the page at all: supplying it changes the method, not just the numbers.

It is worth measuring that resting figure properly. Count for a full sixty seconds first thing in the morning, before you sit up, or take the lowest overnight value your watch reports across a week. A reading taken at your desk after coffee is often 10 to 15 bpm too high, and every zone in your table inherits that error.

Sources: Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited, J Am Coll Cardiol 37:153–156 (2001); Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate: a longitudinal study, Ann Med Exp Biol Fenn 35:307–315 (1957).

Why 220 − age is the wrong place to start

The formula everyone knows has an oddly thin history. It was never the output of an experiment. It surfaced in a 1971 review by Fox, Naughton and Haskell, who assembled maximal heart rate observations from roughly ten earlier studies of mixed quality and small sample size, plotted them, and drew a line through the scatter by eye. The authors offered no claim of precision and were not proposing a prescription tool. It became one anyway, because it is short, memorable and fits on a poster above a treadmill.

Tanaka, Monahan and Seals reopened the question in 2001 with two independent pieces of work: a meta-analysis of 351 published studies covering 18,712 subjects, and a prospective laboratory validation in a further 514 healthy people. Both converged on the same relationship, 208 − (0.7 × age), and both found the same problem with the old rule. The slope is wrong. Maximum heart rate declines by about seven beats per decade, not ten.

Because the slopes differ, the two lines cross. Set 220 − age equal to 208 − (0.7 × age) and they meet at exactly age 40, where both predict 180 bpm. Move away from 40 in either direction and they separate, in opposite directions.

The consequence lands hardest on older exercisers, and it lands in the direction that holds them back. A 70-year-old working from 220 − age is given a maximum of 150 bpm, which caps zone 2 at 105 bpm and starts zone 4 at 120. On the Tanaka figure of 159 bpm, zone 2 runs up to 111 and zone 4 begins at 127. Every prescribed intensity comes out systematically low, so the plan feels easy, the sessions land below the threshold that drives adaptation, and the athlete concludes that training has stopped working. For someone in their twenties the error runs the other way: the old rule flatters the ceiling by a few beats, targets sit slightly high, and the easy days quietly stop being easy.

None of this makes Tanaka exact for you personally. Nothing in this family of equations is, and the next section explains why. The argument for it is narrower and more defensible: it is unbiased across the whole adult age range, and 220 − age is not.

What each zone is actually for

Zones exist so intensity can be prescribed rather than guessed. Each band corresponds to a different physiological state (which fuel dominates, whether lactate is clearing as fast as it is produced, how long the effort can be sustained), and each drives a different adaptation. The table below uses a 40-year-old with a maximum of 180 bpm, calculated as straight percentages of maximum.

The practical failure mode in recreational training is zone 3. It is the pace that feels productive, quick enough to be satisfying and slow enough to sustain, and it is where a surprising proportion of amateur training volume ends up. The problem is that it sits in a physiological dead zone. It accumulates real fatigue, enough to compromise the following day's session, without spending long enough near the threshold to force the adaptations that hard work is meant to buy. Weeks of it produce a plateau that looks like a lack of effort and is actually a misallocation of it.

The alternative, described in the endurance literature as polarised training, is to push the distribution outward from the middle. Roughly 75 to 80 per cent of your weekly volume goes in zones 1 and 2, slow enough that you could hold a conversation and slow enough to be genuinely restorative. The remaining 20 to 25 per cent goes in zones 4 and 5, hard enough that the session has a clear purpose. Zone 3 gets used deliberately (race-pace work, a tempo block in a specific training phase) rather than by default. Most people who make this change find their easy runs become embarrassingly slow and their hard sessions become noticeably harder, which is the point.

If you want the energy cost of those sessions rather than their intensity, our calories burned calculator converts duration and activity into an estimate, and the TDEE calculator folds training into a daily energy total.

Where heart rate zones mislead

Every number on this page descends from one predicted value, and that prediction is a population average. Tanaka's own paper reports a standard deviation of around 10 bpm around the regression line; other analyses put the spread at 10 to 12. In plain terms, roughly a third of people sit more than 10 bpm away from their predicted maximum, and a meaningful minority sit 20 bpm or more either side of it. There are perfectly healthy 45-year-olds with a true maximum of 165 and others at 195. The formula cannot tell you which one you are, because the variation it is missing is between individuals, not within them.

Several other things distort the reading even when the ceiling is right.

• Heart rate lags effort. It takes one to three minutes to catch up with a change in intensity. On short intervals the monitor is still climbing when the effort ends, which makes hard reps look easier than they were. For anything under about three minutes, pace or power is the better guide and heart rate is best read afterwards.
• Cardiac drift. During long or hot sessions, heart rate creeps upward at a constant workload as plasma volume falls and more blood is diverted to the skin. An hour into a warm ride, the same effort can read 10 bpm higher than it did at the start. That is thermoregulation, not extra training stress, and chasing the number down by slowing is usually the wrong response.
• Medication. Beta blockers blunt heart rate at every intensity, often by 20 to 30 bpm, which makes percentage-of-max zones meaningless without a clinician recalibrating them. Some calcium channel blockers and anti-arrhythmics do the same to a lesser degree. Stimulants, including decongestants and high caffeine doses, push in the other direction.
• Everything else in a day. Sleep debt, dehydration, altitude, an incoming infection and simple anxiety all move heart rate at a given workload. A reading that sits 8 bpm above normal on an easy run is more often a signal about recovery than a signal about pace.

The fix is to stop predicting and start measuring. A supervised graded exercise test gives the real number. Failing that, a field test will get close: after a thorough warm-up, run or ride two hard three-minute efforts up a moderate hill with a few minutes of easy recovery between them, and take the highest rate seen near the end of the second. Once you have a measured maximum, or a measured lactate threshold from the average heart rate of the last twenty minutes of a thirty-minute time trial, anchor your zones to that instead. Any measured value beats any formula, including this one.

Training safely at the top of the range

Zones 4 and 5 are, by design, the region where the cardiovascular system is stressed close to its limit. That is what makes them useful and what makes them worth approaching with a little care. If you have known cardiac disease, an arrhythmia, uncontrolled high blood pressure, or a family history of sudden cardiac death, get clearance from a doctor before training at those intensities, and ask for a supervised exercise test rather than relying on a predicted maximum. The same applies if you take beta blockers or any other rate-limiting medication: your zones need recalculating around your medicated response, and no equation on this page accounts for it.

If you are returning to exercise after a long break, or starting for the first time, the sensible route is several weeks in zones 1 and 2 before any threshold work at all. The aerobic system responds quickly; tendons, ligaments and the discipline of pacing take longer. There is no adaptation available in zone 5 that a beginner cannot get more safely from consistent zone 2 volume first.

Stop and seek medical advice for chest pain or pressure, unusual breathlessness at an effort you normally handle, dizziness, fainting, or a heart rate that stays high long after you stop. A monitor that reports a wildly implausible figure is usually a signal artefact (a dry chest strap or a loose optical sensor), but a reading you cannot explain and that comes with symptoms is worth taking seriously rather than troubleshooting.

Common questions