Estimates a moderate-to-vigorous target heart rate zone using the percentage-of-max method, and also the Karvonen (heart rate reserve) method when resting heart rate is given.
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Disclaimer: General formula only. Not medical advice. Dosing decisions belong to a licensed clinician and the product's label.
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Inputs
age_years (number, years, required) min 0 : Age in years
resting_hr (number, bpm, optional) min 0 : Resting heart rate, enables the Karvonen method
Outputs
hr_max (bpm): Estimated maximum heart rate (220 minus age)
pctmax_low (bpm): Lower bound of the percentage-of-max zone (50%)
pctmax_high (bpm): Upper bound of the percentage-of-max zone (85%)
karvonen_low (bpm): Lower bound of the Karvonen zone (50% of heart rate reserve), only when resting_hr given
karvonen_high (bpm): Upper bound of the Karvonen zone (85% of heart rate reserve), only when resting_hr given
Origin of the 220-minus-age maximum heart rate estimate (Annals of Clinical Research, 2026-09-30T19:35:00Z) - Widely used estimate for hr_max; also see Karvonen M, Kentala E, Mustala O. The effects of training on heart rate. Ann Med Exp Biol Fenn. 1957;35:307-315 for the heart-rate-reserve method.
Target Heart Rates Chart (American Heart Association, 2026-09-30T22:29:13Z) - Confirmed live at this final URL (the site redirected the older /fitness/fitness-basics/ path here); moderate intensity is about 50-70% of hr_max and vigorous intensity is about 70-85%; this card reports the full 50% to 85% band as the general target zone.
Worked example and test vectors
Name
Inputs
Answer
worked example
{"age_years":40,"resting_hr":65}
HRmax 180 bpm; percent-of-max zone 90-153 bpm; Karvonen zone 123-163 bpm