Why Your Heart Rate Monitor Shows a Different Max Than the Formula
Standard age-based formulas (like 220 minus age) estimate max heart rate as a population average, but individual max heart rate genuinely varies — sometimes by 10-20 beats per minute or more from what the formula predicts, due to individual physiology, meaning an actual measured max (from a genuine maximal effort) is more accurate for that specific person than any formula-based estimate.
This gap between a formula's prediction and an individual's actual measured max is well-documented and expected, not a sign of anything unusual.
Why formulas are only population averages
A formula like "220 minus age" was derived from average data across a study population — it predicts a reasonable estimate for the average person at a given age, but individual variation around that average is genuinely large, meaning many people's actual max heart rate differs meaningfully from what the formula predicts, in either direction.
What actually determines an individual's true max
Max heart rate is influenced by genetics and individual physiology in ways a simple age-based formula can't capture — it isn't something significantly changed by fitness training itself (unlike resting heart rate, which does improve with fitness), which is why a very fit individual can still have a max heart rate quite different from the formula's prediction for their age.
How to get a more accurate individual number
A supervised maximal exercise test, or a carefully executed field test designed to approach true maximal effort, gives a much more accurate individual max heart rate than any age-based formula — for anyone training zones seriously, using a measured max (once safely obtained) produces more accurate, individually meaningful training zones than a formula-based estimate.