Heart Rate Zones Explained: How to Calculate Yours

Why Bother With Zones?

Left to our own judgement, most of us train at one speed: hard enough to feel like work, easy enough to sustain. It is comfortable, and it is close to useless — too slow to build speed, too fast to build the aerobic base that makes everything else possible.

Heart rate zones replace that guesswork with a number. They tell you when an easy run is genuinely easy and when a hard effort is genuinely hard, which is the difference between training and simply exercising.

Step 1: Estimate Your Maximum Heart Rate

Every zone is a percentage of something, and that something starts with your maximum heart rate. The familiar formula is:

Max HR = 220 − your age

At 40 years old, that gives 180 beats per minute.

Treat That Number With Suspicion

This formula is popular because it is easy to remember, not because it is precise. Individual maximum heart rates scatter widely around the prediction — commonly cited at around ±10 to 12 beats per minute. Two healthy 40-year-olds might genuinely max out at 168 and 192.

A better-evidenced alternative, particularly for older adults, is the Tanaka formula:

Max HR = 208 − (0.7 × age)

The two agree exactly at age 40 and diverge in both directions from there:

Age 20: 200 (traditional) versus 194 (Tanaka)
Age 40: 180 versus 180
Age 60: 160 versus 166
Age 70: 150 versus 159

If you are over 50, the traditional formula probably understates your maximum, and every zone built on it will be set too low.

Step 2: Pick a Zone Method

This choice matters far more than most people realise, because the two standard methods produce genuinely different numbers.

Percentage of Maximum Heart Rate

The simple approach: take percentages straight off your max HR. Easy, but it ignores your fitness entirely.

The Karvonen Method (Heart Rate Reserve)

This one accounts for your resting heart rate, which is where fitness shows up:

Heart Rate Reserve = Max HR − Resting HR
Zone = (HRR × percentage) + Resting HR

Because a fitter person has a lower resting heart rate, Karvonen adapts to the individual rather than treating everyone the same.

The Same Person, Two Very Different Answers

A 40-year-old with a resting heart rate of 60. Max HR is 180, so heart rate reserve is 120.

Zone 1 — Recovery (50–60%): 90–108 by max HR, 120–132 by Karvonen
Zone 2 — Aerobic (60–70%): 108–126 by max HR, 132–144 by Karvonen
Zone 3 — Tempo (70–80%): 126–144 by max HR, 144–156 by Karvonen
Zone 4 — Threshold (80–90%): 144–162 by max HR, 156–168 by Karvonen
Zone 5 — Maximum (90–100%): 162–180 by max HR, 168–180 by Karvonen

Look at Zone 2. It starts at 108 under one method and 132 under the other — a gap of 24 beats per minute. That is not a rounding difference; it is the difference between a brisk walk and a steady run.

This is the single biggest reason people find zone training confusing: they read a Zone 2 figure from one source and check it against a watch using the other. Pick one method and stay with it.

What Each Zone Is For

Zone 1 — Recovery. Warm-ups, cool-downs, and easy days between hard ones.
Zone 2 — Aerobic. Builds the endurance base. Conversational effort, and where the majority of your training time should sit.
Zone 3 — Tempo. Comfortably hard. Useful in moderation, but easy to overuse.
Zone 4 — Threshold. Around the point where lactate begins accumulating faster than you clear it. Sustainable for perhaps an hour at best.
Zone 5 — Maximum. Intervals measured in minutes or seconds, not hours.

Most People Train in the Wrong Zone

The common pattern is to spend nearly every session in Zone 3 — the comfortably-hard middle. It feels productive and delivers surprisingly little, because it is too demanding to accumulate real volume and not demanding enough to drive adaptation.

The widely used alternative is a polarised approach: roughly 80% of your time in Zones 1 and 2, and the remaining 20% genuinely hard in Zones 4 and 5. Easy days properly easy, hard days properly hard.

If your Zone 2 pace feels embarrassingly slow at first, that is the normal experience, and it improves as the aerobic base develops.

What the Formula Cannot Know

Zone boundaries are estimates layered on an estimate. Several things move your heart rate independently of effort:

Medication. Beta blockers in particular lower both resting and maximum heart rate, which invalidates any age-based prediction.
Heat, dehydration and altitude all raise heart rate at the same effort.
Cardiac drift. On a long steady effort, heart rate climbs over time even as pace holds. Late-run readings are not comparable to early ones.
Caffeine, illness, stress and poor sleep all shift resting heart rate, which moves every Karvonen zone with it.

For a figure grounded in your own physiology rather than a population average, a supervised maximum effort test or a lab lactate test beats any formula. Short of that, treat the numbers as a starting frame and adjust by feel.

When to Speak to a Doctor

Get medical advice before starting high-intensity training if you are new to exercise, over 40 and previously inactive, pregnant, or managing a heart condition. Stop and seek help for chest pain, unusual breathlessness, dizziness, or a heart rate that stays high long after you stop.

Conclusion

Estimate your maximum, pick a single method and stick to it, and spend most of your time lower than instinct suggests. If you are over 50, use Tanaka rather than 220 minus your age. Put your age and resting heart rate into a Heart Rate Zone Calculator to get all five zones under both methods, then trust the effort in your legs as much as the number on your wrist.

Try our Heart Rate Zone Calculator

Related Calculators: VO₂ Max Calculator