Your target heart rate tells you how hard to push during exercise so each workout actually delivers the adaptation you want — recovery, fat-burning, endurance, or speed. This calculator builds your zones three ways (Karvonen, percent-of-max, and the Tanaka/Gulati max-HR formulas) so you can see exactly which beats-per-minute range to aim for, and why personalizing for your resting heart rate matters.
Why heart-rate reserve (Karvonen) is more personalized
The simplest method — percent-of-max — just multiplies your estimated maximum heart rate by an intensity percentage. It is easy, but it treats everyone of the same age identically. A sedentary person and a competitive cyclist who are both 35 get the exact same zones, even though their hearts behave very differently.
The Karvonen method fixes this by working from your heart-rate reserve — the gap between your maximum and resting heart rate. A fitter person has a lower resting heart rate and therefore a larger reserve, so Karvonen raises the floor of each zone to match the higher rate they can comfortably sustain. The two methods agree near maximum effort but diverge most at low intensities, which is exactly where easy aerobic and fat-burning work happens.
What each training zone is for
Recovery (50–60%) is for warm-ups and active recovery. Fat-burn / Zone 2 (60–70%) is a light, conversational pace that builds aerobic base and trains the body to use fat for fuel — the backbone of endurance training. Aerobic (70–80%) is moderately hard, sustainable effort that improves overall cardiovascular fitness; it is the default recommendation for general health. Anaerobic (80–90%) raises your lactate threshold and speed. Maximum (90–100%) is all-out effort reserved for short intervals.
A common, evidence-backed structure is polarized training: spend most of your time in the easy aerobic and fat-burn zones and reserve a smaller slice for hard anaerobic and maximum work, rather than grinding in the moderate middle.
Limits, accuracy, and when to see a professional
Every age-based max-HR formula is an estimate with an individual variation of roughly ±10–12 bpm, so your true maximum may differ. Beta-blockers and other medications can lower both your max and resting heart rate, making predicted zones inaccurate. Heart-rate response also lags behind effort and drifts upward in heat or dehydration (cardiac drift).
Treat these zones as a starting guide, not a medical prescription. If you have a heart condition, are pregnant, take medication that affects heart rate, or are starting exercise after a long break, talk to a doctor before following intensity targets — and stop and seek care if you feel chest pain, dizziness, or unusual shortness of breath.