Why 208 − 0.7 × age, not 220 − age
The familiar "220 minus age" was never derived from research; it appeared in a 1970s summary and stuck. Tanaka's 2001 meta-analysis of 351 studies produced 208 − 0.7 × age, which fits measured data considerably better, especially for people over 40.
Even so, individual maximum heart rates vary by around ±10 bpm from any formula. A properly conducted maximal effort test gives your real number.
The Karvonen method
Entering a resting heart rate switches the zones to the Karvonen formula, which works from heart rate reserve — the gap between resting and maximum — rather than from maximum alone.
This matters because a fit person with a resting rate of 45 and an unfit person at 75 should not train at the same absolute heart rate for the same relative effort. Measure your resting rate immediately on waking, before getting up.
Frequently asked questions
Why is zone 2 so popular? +
It builds mitochondrial density and fat oxidation with low recovery cost, so large volumes can be sustained week after week. Most endurance athletes spend the majority of their training there.