Heart rate
zones

Enter your age and get five training zones in beats per minute — by percent of max heart rate or by Karvonen heart-rate reserve. With the reason those two methods disagree on the same zone.

How the math works

Zones are a percentage of a ceiling. The two methods differ in what that ceiling is. Percent of max HR scales your estimated maximum directly. Karvonen scales your reserve — the gap between max and resting — and adds resting back, which pulls every zone upward for anyone whose resting rate is above zero.

The five-zone bands are the ACSM percentages: Zone 1 recovery 50–60%, Zone 2 aerobic 60–70%, Zone 3 tempo 70–80%, Zone 4 threshold 80–90%, Zone 5 VO2 max 90–100%. Tanaka is the default here because its meta-analysis was tighter than 220 − age; the Gulati equation was validated specifically on women.

Worked example

A 35-year-old runner, using Tanaka: max HR = 208 − 0.7 × 35 = 184 bpm. The five zones by percent of max HR:

• Zone 1 — Recovery (50–60%): 92–110 bpm
• Zone 2 — Aerobic (60–70%): 110–129 bpm
• Zone 3 — Tempo (70–80%): 129–147 bpm
• Zone 4 — Threshold (80–90%): 147–166 bpm
• Zone 5 — VO2 max (90–100%): 166–184 bpm

Now the same runner by Karvonen, with a resting HR of 60 bpm. Reserve = 184 − 60 = 124 bpm, so Zone 2 becomes (124 × 0.60 + 60) to (124 × 0.70 + 60) = 134–147 bpm. Same label, a band that starts 24 bpm higher. That gap is the single most confusing thing about heart-rate zones, and most calculators never mention it because they only run one method.

Zones are beats per minute, which is the same number everywhere — there is no imperial-versus-metric conversion here. Units only re-enter when you pair a zone with pace: a runner holding easy Zone 1–2 effort might sit around 9:30–10:00/mi (5:54–6:13/km), the Daniels easy band for a 3:30-marathon runner (Scenario E2). The pace has two unit forms; the heart rate has one.

When this calculator is wrong

The most common mistake isn't the number — it's how the week is spent around it. Polarised-training research (Seiler 2010 and subsequent) points to roughly 80% of endurance work in Zone 1–2 and about 20% in Zone 4–5, with very little in Zone 3. Most runners invert the middle: too little easy Zone 2, too much Zone 3 "grey zone" that feels productive — moderately hard, lots of breathing — but drives aerobic adaptation less than easy work and VO2 max less than hard intervals. The exception is time-crunched athletes with fewer than four sessions a week, for whom some Zone 3 is unavoidable and probably fine.

• The max-HR estimate has a wide error band. The 220 − age formula carries a population spread of about 10–12 bpm; Tanaka is tighter but still 5–8 bpm off for many people. That's enough to put a formula-built zone a full zone away from your real one. If your zones matter, do a max-effort test or use a lab value rather than trusting the estimate.
• %HRmax and Karvonen are not interchangeable. As the worked example shows, Karvonen zones sit higher because they factor in resting HR. Pick one method and stay with it; comparing a %HRmax Zone 2 against a Karvonen Zone 2 will look like a contradiction when it's just two definitions.
• Medication and conditions break the model. Beta-blockers lower both resting and max heart rate, so formula zones no longer describe your effort. The talk test — Zone 2 is a pace you can hold a conversation at — is a better anchor than a bpm target in that case, and a clinician's guidance better still.

What to do with the result

Use Zone 2 as the anchor. Set most of your easy running to the Zone 2 band and confirm it with the talk test: if you can't speak in full sentences, you've drifted into Zone 3 regardless of what the watch says. Keep hard sessions clearly in Zone 4–5 rather than letting them sag into the grey zone. Then calibrate: over two or three weeks, note the heart rate at which your easy pace stops feeling easy and adjust the band to match your body, not the formula. Re-run the numbers if you get a lab or field max-HR test, or when a training block changes your resting rate.

Common questions

How do I calculate my heart rate zones?

Estimate your max heart rate from age (Tanaka: 208 − 0.7 × age), then take percentages of it: Zone 1 is 50–60%, Zone 2 is 60–70%, up to Zone 5 at 90–100%. For a 35-year-old that puts Zone 2 at 110–129 bpm. The Karvonen method uses your resting heart rate too and shifts the zones higher.

Is 220 minus age accurate for max heart rate?

It's a rough average. The 220 − age formula (Fox-Haskell) has a population spread of about 10–12 bpm, meaning it can be off by a full training zone for a given person. Tanaka's 208 − 0.7 × age is tighter but still 5–8 bpm off for many. A max-effort test or lab value beats any formula.

Should I use %HRmax or the Karvonen method?

Either works — just don't mix them. Karvonen factors in resting heart rate, so its zones sit higher: a 35-year-old's Zone 2 is 110–129 bpm by %HRmax but 134–147 bpm by Karvonen. Karvonen individualises better if you know your true resting rate; %HRmax is simpler. Pick one and stay consistent.

What is Zone 2 and why does everyone talk about it?

Zone 2 is 60–70% of max heart rate — an easy, conversational aerobic effort. Polarised-training research suggests roughly 80% of endurance work should sit in easy Zone 1–2, which is why it gets the attention. The catch is that most runners drift above it into Zone 3, where the training stimulus is less efficient.

Why are my zones different on my watch or another calculator?

Three reasons: a different max-HR formula (220 − age versus Tanaka versus a measured value), a different method (%HRmax versus Karvonen reserve), or a device using its own recorded max. None is more "correct" in the abstract — a measured max HR and a consistent method matter more than which calculator you use.

Do beta-blockers change my heart rate zones?

Yes. Beta-blockers and some other medications lower both resting and maximum heart rate, so age-based zones no longer match your actual effort. Use perceived effort or the talk test instead, and ask the prescribing clinician how to gauge intensity while on the medication.