Heart Rate Zone Calculator (Karvonen)

Understanding the heart rate zone calculator — concept and principle

Heart rate zones split your training intensity into five bands, from easy recovery to all-out effort. This calculator uses the Karvonen method, which builds the zones from your heart rate reserve, the gap between your resting and maximum heart rate. Runners and cyclists use them to keep easy days easy and hard days hard.

The zones split the upper half of the gap between resting and maximum heart rate.

How it is calculated

Target HR = resting HR + intensity × (max HR − resting HR)

Max HR: estimated from age with the formula you choose: Tanaka 208 − 0.7 × age, classic 220 − age, or Gulati 206 − 0.88 × age for women.
Resting HR: measured in the morning before getting up, in beats per minute (bpm).
Intensity: the zone boundaries 50, 60, 70, 80, 90 and 100% of heart rate reserve.

Zone 1 is 50–60% (recovery), zone 2 60–70% (endurance), zone 3 70–80% (tempo), zone 4 80–90% (threshold) and zone 5 90–100% (maximum).

The principle

Your heart never goes below its resting rate, so the part of the range you can actually use for exercise is the reserve between rest and maximum. Karvonen's 1957 study related training intensity to this reserve. Percentages of heart rate reserve track percentages of oxygen uptake reserve fairly closely, which is why they describe metabolic effort better than simple percentages of max HR. A fitter person with a lower resting rate therefore gets different zones at the same age.

Worked example

Inputs: age 35, resting HR 60, Tanaka formula.
Max HR = 208 − 0.7 × 35 = 183.5, displayed as 184.
Reserve = 183.5 − 60 = 123.5.
Zone 1: 60 + 0.5 × 123.5 = 121.75 → 122, and 60 + 0.6 × 123.5 = 134.1 → 134, so 122–134 bpm.
The same steps give zone 2 134–146, zone 3 146–159, zone 4 159–171 and zone 5 171–184 bpm.

Each point is the calculator re-run with only “Age” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Age	Max heart rate
8.75	202
17.5	196
26.2	190
35	184
43.8	177
52.5	171
70	159

How to read the result

Most endurance plans spend the bulk of training time in zones 1–2, with smaller doses in zones 4–5. The ACSM describes 40–59% of heart rate reserve as moderate and 60–89% as vigorous intensity. Heart rate lags behind effort by a minute or two at the start of an interval and drifts upward on long or hot sessions.

Common mistakes

Measuring resting HR after coffee, stress or walking around.
Treating an age-based max HR as exact; it can be off by 10 bpm or more.
Comparing with watch zones, which often use % of max HR or lactate threshold instead of heart rate reserve.

Keep in mind: This is an estimate for training, not a diagnosis. Beta-blockers and some other medicines lower heart rate and make these zones invalid. If you have a heart condition, symptoms during exercise or are starting vigorous training after years of inactivity, talk to a doctor first.

Frequently asked questions

How do I measure resting heart rate?

Count your pulse for 60 seconds just after waking, still lying down, on several mornings and use the average.

Which max HR formula should I choose?

Tanaka is a good general choice for adults; Gulati was derived from women. A supervised test or a hard field test gives your real value.

Sources: Karvonen M. J., Kentala E., Mustala O., Annales Medicinae Experimentalis et Biologiae Fenniae, 1957 · Tanaka H., Monahan K. D., Seals D. R., Journal of the American College of Cardiology, 2001 · American College of Sports Medicine, ACSM's Guidelines for Exercise Testing and Prescription

Checked 8 Nov 2026. Karvonen 1957; Tanaka et al., JACC 2001; Gulati et al., Circulation 2010.

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