THE NUMORIX GUIDE
How to use the Heart Rate Calculator
Last reviewed September 14, 2026
What this calculator does
The default maximum heart rate is round(220 - age).
Formula and method
The default maximum heart rate is round(220 - age). When a resting heart rate is supplied, the engine calculates a Karvonen-style target maximum as round((maxHr - restingHr) * 0.85 + restingHr) and uses that value for zones. Zones are 50-60%, 60-70%, 70-80%, 80-90%, and 90-100% of the selected maximum, rounded to whole bpm.
Variables and inputs
Age must be 1-120 years. Resting heart rate is optional and entered in beats per minute; the checkbox activates the alternate calculation. The table labels zones Warm Up, Fat Burn, Aerobic, Anaerobic, and VO2 Max, while the large result continues to show the age-based maxHr even when zone ranges use karvonenMax.
Worked example
At age 30 without a resting rate, max HR = 220 - 30 = 190 bpm. The zones are 95-114, 114-133, 133-152, 152-171, and 171-190 bpm after rounding. With resting HR 60, the alternate maximum is round((190 - 60) * 0.85 + 60) = 171 bpm and the zones use 171.
How to interpret the result
These are broad training references, not measured physiological limits. The zone names describe the engine's labels; they do not prove that a particular intensity is using a specific fuel source or that a person has reached VO2 max.
Common mistakes to avoid
Enter a genuinely resting value rather than a post-exercise pulse, and remember that the displayed Max Heart Rate can remain 190 while the Karvonen table uses 171. Do not train to a calculated maximum when symptoms or medical restrictions are present.
Assumptions and limitations
The 220-age formula has substantial individual error. The optional calculation uses one 85% target rather than full heart-rate-reserve zone formulas, rounds each boundary, and treats a resting value of zero as missing. Medications, illness, fitness, temperature, and cardiac conditions can make these zones inappropriate.