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Heart Rate Zone Calculator

Train the right system, not just the right amount.

"220 minus age" zones ignore the biggest variable in cardiac fitness: your resting heart rate. This calculator uses the Karvonen (heart rate reserve) method — the approach taught in ACSM and NASM certifications — which scales every zone to your actual fitness level. Five zones, from active recovery to redline, personalized in two inputs.

Why people use this

Runners and cyclists use this to keep easy days truly easy (Zone 2 is where the aerobic engine gets built), and trainers use it to write cardio prescriptions. It exists because "220 minus age" zones ignore resting heart rate — the biggest fitness variable.

How it works

1. Enter your age and resting heart rate (measure it lying down, right after waking).
2. The calculator estimates max HR (220 − age), then your heart rate reserve (max − resting).
3. Each zone is a percentage band of that reserve added back to your resting rate.
4. Zone 2 (60–70%) is the endurance base zone where most training time should live.

Common questions

Why is Karvonen better than simple percentage-of-max zones?

Two 40-year-olds can have resting heart rates of 50 and 80 — a simple percentage gives them identical zones, which is wrong. Karvonen anchors to heart rate reserve, so a fitter heart earns lower, more accurate zone boundaries.

How much of my training should be Zone 2?

The 80/20 rule used by most endurance coaches: roughly 80% of weekly training time in Zones 1–2 (conversational pace) and 20% in Zones 3–5. Zone 2 feels almost too easy — that is the point.

What if I know my actual max heart rate?

Use it: replace (220 − age) with your tested max from a hard hill-repeat or race effort. The reserve method stays the same; the tested max just removes the estimation error.

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