Body FormulaFitness

Heart Rate Zone Calculator

Five training zones by the Karvonen reserve method and by plain percentage of maximum. On the worked example they put the bottom of zone 2 twenty-four beats apart.

Where the maximum comes from
Maximum heart rate

An age estimate carries about ±10 bpm, which moves every zone boundary by six or seven beats. A measured maximum is worth far more here than the choice of zone method.

years

Used only when the maximum is estimated.

bpm

The highest figure you have actually seen on a monitor in a hard effort.

bpm

Karvonen needs this. Without it the page falls back to percentage of maximum and says so.

Zone method

Both are computed either way. This chooses which one the table leads with.

Zone 2 — easy aerobic134–147bpm

Karvonen heart-rate reserve, from Tanaka's estimate of 184 for age 35 and a resting rate of 60

Maximum used 184 bpm
Heart-rate reserve 124 bpm
Zone 4 threshold 159–172 bpm

Zone Karvonen % of max What it is for
1 — Recovery 122–134 92–110 Warm-up, cool-down and easy movement between hard days. (50–60%)
2 — Easy aerobic 134–147 110–129 Conversational effort. Most of a distance week sits here. (60–70%)
3 — Steady 147–159 129–147 Comfortably hard, and the easiest zone to spend too long in. (70–80%)
4 — Threshold 159–172 147–166 Around the effort you could hold flat out for about an hour. (80–90%)
5 — Maximal 172–184 166–184 Intervals of a few minutes. Not sustainable for long by design. (90–100%)

The two methods diverge most in the easy zones: the gap is (1 − the zone fraction) × your resting heart rate, so it closes only at maximum and grows with your resting rate. That is why a runner told to train in “zone 2” by two different devices gets two different instructions.

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Last checked

The two methods, written out

Karvonen, Kentala & Mustala (1957) — the heart-rate reserve method. Reserve is the room between resting and maximum, and the zone is a fraction of that room added back on top of resting:

target = HRrest + fraction × (HRmax − HRrest)

Percentage of maximum — the simpler one, and the one most equipment uses:

target = fraction × HRmax

They are not variations on a theme. They anchor at different points, and they give materially different answers for the same person.

Worked example: maximum 184, resting 60

Reserve = 184 − 60 = 124 bpm.

Bottom of zone 2, at 60%:

  • Karvonen: 60 + 0.60 × 124 = 60 + 74.4 = 134 bpm
  • Percentage of maximum: 0.60 × 184 = 110 bpm

Twenty-four beats apart. At 110 bpm this runner is walking; at 134 they are running an easy aerobic pace. Told to “train in zone 2”, two devices using the two methods would give them completely different sessions.

The gap has a simple closed form: at a zone fraction f it is exactly (1 − f) × your resting heart rate. So it closes to nothing at 100%, where both methods return the maximum by definition, it widens as the zones get easier, and it is proportional to your resting heart rate. At a resting rate of 80 the bottom of zone 2 comes out 32 beats apart; at 60 it is 24 beats; at a well-trained 40 it is 16. The disagreement never disappears and it is never small.

Which method to use

Karvonen is the better default, because it takes account of the fact that your heart rate does not start at zero. Percentage of maximum implicitly treats 0 bpm as the bottom of the scale, which nobody's is; Karvonen anchors on your actual resting rate, so the zones scale with the range you genuinely operate over.

The reason percentage of maximum survives is that it needs one input instead of two, which suits a device that does not know your resting rate. If your watch's zones feel far too easy, this is usually why.

Whichever you use, use it consistently. Switching methods halfway through a training block makes every session log incomparable with the one before it.

Getting the two inputs right

Maximum heart rate. A measured figure is worth more here than the choice of method. An age estimate carries a residual of about ±10 beats, and ten beats of error in the maximum moves every Karvonen boundary by six or seven — roughly a third of a zone's width. The max heart rate page runs five published equations and prints the spread; if you have ever seen a real maximum on a monitor at the end of a hard race, use that instead.

Resting heart rate. Taken lying still, before getting up, ideally averaged over several mornings. A reading taken after coffee, after standing up, or after a bad night can be ten to fifteen beats high, and it drags every Karvonen zone up with it. This is the input people most often get wrong, and it is the easy one to get right.

What the five zones are for

Zone 1, recovery. Warm-up, cool-down, and genuinely easy movement between hard days.

Zone 2, easy aerobic. Conversational: you can speak in full sentences. Most of a distance runner's week belongs here, and the most common training error is running it too hard.

Zone 3, steady. Comfortably hard. Useful in moderation and the easiest zone in which to accumulate junk mileage — hard enough to tire you, not hard enough to drive adaptation.

Zone 4, threshold. Roughly the effort you could sustain flat out for about an hour.

Zone 5, maximal. Intervals of a few minutes at most. Not sustainable, by design.

The boundaries are conventions, not physiology. Five zones at ten-percentage-point intervals is one popular scheme; three-zone and seven-zone models exist and are equally defensible. Nothing physiological happens at exactly 70%.

Why there is no fat-burning zone here

Because the claim behind it does not survive being stated carefully. At low intensity a larger share of the energy you use comes from fat; at higher intensity a smaller share of a much larger total does, and the total is usually what matters. The label is a real physiological observation about substrate mix that has been repackaged as a training instruction it does not support, so it does not appear on this page.

Limitations, stated plainly

Heart rate lags effort by a minute or two, drifts upward over a long session at constant pace, and rises in heat, at altitude, when dehydrated, when under-slept and after caffeine. It can be five to ten beats different for the same effort on two consecutive days for no reason you will ever identify, which is why heart rate is a good guide over weeks and a poor one minute to minute.

Chest straps are reliable; optical wrist sensors frequently misread during intervals and sometimes lock onto cadence rather than pulse, which produces a plausible-looking number that is not your heart rate at all.

Zone boundaries are training conventions applied to two estimated inputs. They are not medical advice and nothing on this page interprets a heart rate as a sign of anything. If you take any medication that affects heart rate, zones set from these equations may not describe your training at all, and that is a conversation with a professional rather than with a calculator.

Common questions

What is the Karvonen formula?

Target heart rate = resting + fraction × (maximum − resting), published by Karvonen, Kentala and Mustala in 1957. The bracketed term is your heart-rate reserve — the range your heart actually works over. It gives higher and generally more realistic zone boundaries than taking a percentage of maximum alone.

Why are my watch's zones different from these?

Almost always because your watch is using percentage of maximum and this page is defaulting to Karvonen. On the worked example here the two put the bottom of zone 2 twenty-four beats apart. The size of that gap is (1 − the zone fraction) × your resting heart rate, so it is largest for people with a high resting rate and it shrinks — but never to zero — as your resting rate comes down. Check which method your device uses before deciding either is wrong.

What heart rate is zone 2?

It depends entirely on your maximum and your resting rate, which is why there is a calculator on this page rather than a number. For the worked example — maximum 184, resting 60 — Karvonen puts zone 2 at 134 to 147 bpm. The practical check is conversational effort: if you cannot speak in full sentences you are above it, and if you could sing you are probably below it.

Do I need my resting heart rate?

For Karvonen, yes. Without a usable resting rate this page falls back to percentage of maximum and tells you it has done so, rather than substituting a guess. Take it lying still before getting up, averaged over several mornings; a reading taken after coffee or after standing can be ten to fifteen beats high and drags every zone up with it.

Is there a fat burning zone?

Not in the form the label implies. At lower intensities a larger proportion of your energy comes from fat, but a smaller proportion of a much larger total at higher intensity often means more fat used overall — and over days and weeks, total energy balance decides the outcome rather than which fuel a particular session burned. It is a real observation about substrate mix, sold as a training instruction it does not support.

How many heart rate zones should there be?

Five at ten-point intervals is the common scheme and the one used here. Three-zone models built around the two ventilatory thresholds and seven-zone models used in cycling are equally defensible. The boundaries are conventions for organising training, not physiological events — nothing changes at exactly 70%.

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