The Karvonen formula
Max HR ≈ 220 − age. Heart-rate reserve (max minus resting) is scaled by intensity: target = reserve × % + resting. Using your resting rate personalises the zones far better than age alone.
The five zones
50% warm-up, 60% fat burn, 70% aerobic endurance, 80% threshold, 85%+ peak. Most steady training lives in zones 2–3.
An estimate, not a prescription
Real maximum heart rates vary ±10–15 bpm between people. Treat zones as guidance — and check with a clinician before hard training if you have heart risk factors.
Frequently Asked Questions
What is the Karvonen formula?
Target HR = (max HR − resting HR) × intensity % + resting HR — it personalises zones with your resting rate.
Which zone burns the most fat?
Zone 2 (~60%) burns the highest <i>share</i> of fat, but harder zones burn more total calories. Mix both.
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