Heart rate zones calculator (Z1 to Z5)

Heart rate zones structure your endurance training. Each zone matches an intensity (% of max heart rate) and a purpose: recovery, aerobic base, tempo, threshold, VO2max.

The calculator returns ranges in beats per minute (bpm) using two methods: simple HRmax (220 - age) or Karvonen (factors in resting HR for individual precision).

The two methods

• Simple HRmax: zone bpm = HRmax × percentage. Population approximation, fine to start.
• Karvonen: zone bpm = (HRmax - resting HR) × percentage + resting HR. More precise, integrates your cardiac reserve.

What each zone trains

• Z1 (50-60%): recovery, warmup, easy unblocking. Easy conversation possible.
• Z2 (60-70%): aerobic base, long runs. The volume zone.
• Z3 (70-80%): marathon and half pace. Mildly breathing harder, in control.
• Z4 (80-90%): anaerobic threshold, long intervals (1,000 to 3,000 m). Uncomfortable but sustainable.
• Z5 (90-100%): VO2max, short intervals (200 to 800 m). Very short, very hard.

How to measure resting HR

At rest, lying down, in the morning upon waking. Count pulses for 60 seconds (or 30 sec × 2). For better accuracy, do it 3 consecutive mornings and average.

Low resting HR (<60 bpm) generally signals good cardiovascular adaptation. Above 80 bpm with fatigue or poor sleep, exercise caution.

Limits of 220 - age

The 220 - age formula is a population-level approximation. Your real HRmax can differ by ±10 bpm. A graded exercise test (cardiologist or sport lab) remains the reference for trained athletes.

FAQ

Why does my HR sometimes exceed my theoretical HRmax?

Either your real HRmax is higher than 220 - age (common), or your watch skips beats / catches noise. Recompute using the highest value measured in competition.

Karvonen or simple HRmax?

Karvonen as soon as you know resting HR. More precise, especially at low intensities (Z1-Z2) where simple HRmax underestimates effort.