Your results display five heart rate training zones, each defined as a range of beats per minute (bpm) calculated using the Karvonen method. Zone 1 (50–60% of heart rate reserve) is a very light recovery zone. Zone 2 (60–70%) is the aerobic base-building zone where fat oxidation is highest relative to effort. Zone 3 (70–80%) targets cardiovascular fitness and aerobic capacity. Zone 4 (80–90%) develops lactate threshold and anaerobic capacity. Zone 5 (90–100%) represents near-maximal effort used for short, high-intensity intervals.

The Karvonen method produces more personalized zones than simple percentage-of-max-HR methods because it accounts for your resting heart rate. Two people of the same age but different fitness levels will get different target ranges, reflecting the fact that a fitter heart has a larger heart rate reserve to work with.

Use this calculator when designing a structured cardiovascular training program or when you want to ensure you are training at the right intensity for your goals. It is especially useful for endurance athletes following periodized training plans that prescribe specific zone targets for different workout types — for example, long slow runs in Zone 2 or threshold intervals in Zone 4.

It is also helpful for beginners who may tend to train too hard on easy days and too easy on hard days. Heart rate zone training helps enforce the intensity discipline that underpins effective aerobic development. The widely recommended 80/20 training distribution (80% of training time in Zones 1–2 and 20% in Zones 3–5) is built on this framework.

The maximum heart rate estimate (220 minus age) has a standard deviation of approximately 10–12 bpm, meaning your true max HR could be significantly higher or lower than predicted. This error propagates into all zone calculations. For more accurate zones, use a lab-tested or field-tested maximum heart rate rather than the age-based estimate.

Resting heart rate should be measured under standardized conditions — ideally first thing in the morning, before caffeine, and after adequate sleep. Stress, illness, dehydration, and certain medications (especially beta-blockers) can alter resting heart rate and distort the zone calculations. Additionally, heart rate zones are population-level approximations. The actual metabolic thresholds (aerobic threshold, lactate threshold) vary between individuals and do not always align precisely with percentage-based HR zones. For competitive athletes, lactate testing or ventilatory threshold testing provides more precise training targets.