Maximum heart rate and training zones, using Tanaka and the Karvonen method.
This calculator uses the Tanaka formula: 208 − 0.7 × age. For a forty-year-old that gives 180 beats per minute. The older 220 − age rule is simpler but underestimates maximum heart rate in older people; the Tanaka study of 2001 corrects it.
It is an average with a wide spread — an individual's true maximum can differ by ten beats per minute or more in either direction. Only a supervised exercise test gives a precise figure. The Tanaka formula is a good starting estimate rather than a personal measurement.
The zones are percentage bands of maximum heart rate corresponding to different intensities. The lower bands around 50–70% build base endurance and can be held for a long time; above 85% builds speed but can only be sustained briefly. The top of the scale is the maximum heart rate, estimated here with the Tanaka formula.
Heat, humidity, dehydration, sleep, stress, caffeine and illness all move heart rate, and the difference can be ten beats per minute or more. That is why experienced athletes read the Tanaka-derived zones alongside perceived effort rather than trusting the number on the watch alone.