Heart Rate Zones Calculator (Karvonen)

Heart-rate training zones

Maximum heart rate (HRmax) is estimated by Fox HRmax = 220 − age or by the more accurate Tanaka HRmax = 208 − 0.7·age. The Karvonen method uses heart-rate reserve: HRzone = HRrest + %·(HRmax − HRrest). Standard zones: Z1 50-60% (recovery), Z2 60-70% (aerobic base), Z3 70-80% (tempo), Z4 80-90% (threshold), Z5 90-100% (VO2max). Example: age 30, HRrest 60 → Fox HRmax 190; Karvonen Z2 lower = 60 + 0.60·(190−60) = 138 bpm. Polarised training (Seiler) prescribes about 80% of weekly volume in Z1-Z2 and 20% in Z4-Z5, leaving little in Z3 — a pattern that consistently outperforms threshold-only training in endurance athletes.

Applications

Used in running, cycling, swimming, triathlon and general cardio conditioning for pacing intervals and long efforts. Smartwatches and platforms (Garmin, Polar, Strava, Coros, Apple Watch) auto-calculate zones from HRmax and HRrest. Also used in cardiac rehabilitation, weight-loss programmes and supervised return-to-activity protocols.

FAQ

Fox or Tanaka? Tanaka has lower error for adults above 40; Fox is fine for a quick estimate. A field test or lab test is more accurate than either formula.

Why use Karvonen instead of % of HRmax? Karvonen accounts for resting heart rate, so fit users get more realistic zones — % of HRmax alone tends to underestimate intensity in trained athletes.

Should I train mostly in Z3? No. The Z3 "grey zone" is harder than easy training but lighter than threshold work. Most evidence supports the 80/20 polarised model.

How do I measure HRrest correctly? Take the average over 1 minute right after waking, while still in bed, for several days.