Heart Rate Zones

The Karvonen formula (Heart Rate Reserve method) calculates personalised training zones: Target HR = (Max HR − Resting HR) × Intensity% + Resting HR. It accounts for your resting heart rate, making it more accurate than simple "% of max HR" formulas. Two people with the same max HR but different resting HRs will have different zone boundaries.

This calculator uses the Tanaka formula: Max HR = 208 − (0.7 × age), which is more accurate than the classic "220 − age" formula. For a 35-year-old: Max HR = 208 − 24.5 = 183.5 ≈ 184 bpm. Your true max HR can only be determined via a maximal exercise test.

Zone 1 (50–60% HRR): Very light, warm-up and recovery. Zone 2 (60–70% HRR): Easy aerobic, fat burning, base building. Zone 3 (70–80% HRR): Aerobic, improving cardiovascular efficiency. Zone 4 (80–90% HRR): Anaerobic threshold, improving race pace. Zone 5 (90–100% HRR): Maximum effort, sprint intervals.

Zone 2 (roughly 60–70% of HRR, or "conversational" pace) builds mitochondrial density, fat oxidation capacity, and aerobic base. Endurance coaches like Dr. Inigo San Millan and Peter Attia recommend 80% of total training volume in Zone 2. It improves VO2 max and metabolic efficiency with lower injury risk than high-intensity work.

For adults: 60–100 bpm is the normal range (AHA). Athletes often have resting HRs of 40–60 bpm. A lower resting heart rate generally indicates better cardiovascular fitness. Resting HR above 100 (tachycardia) warrants medical evaluation. Check yours first thing in the morning before getting out of bed for the most accurate reading.