Target Heart Rate Zone Calculator
Calculate your personalised heart rate training zones using the Karvonen formula. Know exactly what heart rate to target for fat burn, aerobic fitness, or peak performance.
Heart Rate Training Zones Guide
The Karvonen Formula
The Karvonen formula uses heart rate reserve (HRR = max HR − resting HR) to calculate personalised zones. Target HR = resting HR + (% intensity × HRR). This is more accurate than simple %max HR because it accounts for individual fitness level. A fit person with a low resting HR has a larger heart rate reserve, meaning their Zone 2 training occurs at a higher actual heart rate than someone less fit at the same age.
Zone 2 Training — The Foundation
Zone 2 (60–70% HRR, roughly 120–140 bpm for most adults) is the most important training zone for building aerobic base, fat oxidation, and mitochondrial density. It should feel like a conversational pace — you can speak in full sentences but are breathing noticeably. Elite endurance athletes spend 75–85% of their training volume in Zone 2. Research shows this polarised training approach (mostly Zone 2 with some Zone 5) produces better results than training primarily at moderate-hard intensity.
Fat Burning Zone Reality
The 'fat burning zone' (lower intensity exercise) burns a higher percentage of calories from fat, but not the most total fat. At 60% max HR, perhaps 60% of energy comes from fat. At 80% max HR, only 35% from fat but total energy expenditure per minute is much higher. A 60-minute run at 75% intensity burns more total calories and more total fat than a 60-minute walk at 50% intensity. The 'fat burning zone' myth misleads people into thinking lower-intensity is better for fat loss — total calorie e
Measuring Heart Rate
Chest strap monitors (Polar, Garmin HRM) are the most accurate — optical wrist-based sensors in smartwatches can be 5–15 bpm off at high intensities due to movement artefact. For serious training, a chest strap provides the precision needed for accurate zone training. Manual pulse check: find pulse at wrist or neck, count for 10 seconds, multiply by 6. During exercise, find a point where you can hold still briefly (between intervals) for a more accurate count.
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