THE NUMORIX GUIDE
How to use the Target Heart Rate Calculator
Last reviewed September 14, 2026
What this calculator does
The engine estimates maximum heart rate as round(220 - age), then computes heart-rate reserve as max HR - resting HR.
Formula and method
The engine estimates maximum heart rate as round(220 - age), then computes heart-rate reserve as max HR - resting HR. For a selected intensity p, the lower target is resting HR + reserve x p/100 and the upper target uses min(p + 10, 100). It also reports five Karvonen-style zones at 50-60%, 60-70%, 70-80%, 80-90%, and 90-100% of reserve, with each endpoint rounded to a whole bpm.
Variables and inputs
Enter age in years, resting heart rate in beats per minute, and target intensity from 50% to 100%. The UI accepts age 1-120, resting HR 30-200 bpm, and intensity in 5% slider steps. The result includes max HR, HR reserve, a target interval, and five zone intervals.
Worked example
For age 30, resting HR 60 bpm, and 70% intensity, max HR = 220 - 30 = 190 bpm and reserve = 190 - 60 = 130 bpm. The target is 60 + 130 x 0.70 = 151 bpm through 60 + 130 x 0.80 = 164 bpm. The adjacent zones include moderate 151-164 bpm and hard 164-177 bpm.
How to interpret the result
The target is an estimated training range relative to resting heart rate. It is useful for describing effort, but the displayed bpm is not a personal medical limit and does not account for whether the age-based maximum is accurate for that person.
Common mistakes to avoid
Measure resting HR after genuine rest rather than immediately after activity or caffeine. Do not substitute an exercise heart rate for resting HR, and do not confuse 70% of maximum HR with 70% of heart-rate reserve; this engine uses the latter for its target calculation.
Assumptions and limitations
The 220 - age maximum-HR equation has substantial individual error, and the zones are broad rounded estimates. Medication, arrhythmia, pregnancy, cardiovascular disease, fitness level, heat, and sensor error can change safe or useful training intensity. Stop exercise for concerning symptoms and follow clinician or exercise-professional advice when appropriate.