Heart Rate Zone Calculator

Maximum heart rate (MHR) is the highest number of times your heart can beat per minute during exercise. The most widely used formula is 220 − age. Example: a 35-year-old has an estimated MHR of 220 − 35 = 185 bpm. This is an estimate — actual MHR varies by up to ±10–12 bpm between individuals. A lab stress test gives the most accurate measurement.

Heart rate zones divide exercise intensity into 5 bands based on a percentage of your maximum heart rate. Zone 1 (50–60% MHR): very light recovery. Zone 2 (60–70% MHR): fat burning, aerobic base. Zone 3 (70–80% MHR): cardio/aerobic. Zone 4 (80–90% MHR): anaerobic threshold. Zone 5 (90–100% MHR): maximum effort. Training in different zones produces different physiological adaptations.

Zone 2 (60–70% of max HR) is the cornerstone of endurance training. At this intensity, your body primarily uses fat as fuel, builds mitochondrial density, and improves aerobic efficiency — all without significant recovery stress. Elite endurance athletes spend 70–80% of their training volume in Zone 2. It's the zone where you can speak in full sentences but are noticeably working. Benefits accumulate over weeks and months of consistent Zone 2 training.

The Karvonen formula gives more personalized heart rate zones by accounting for your resting heart rate. Formula: Target HR = ((MHR − Resting HR) × Intensity%) + Resting HR. This is called the Heart Rate Reserve (HRR) method. Example: MHR = 185, resting HR = 60, Zone 2 target at 65%: ((185−60) × 0.65) + 60 = (125 × 0.65) + 60 = 81.25 + 60 = 141 bpm. The Karvonen method gives a higher Zone 2 target than the simple percentage method for fit individuals with low resting heart rates.

Zone 2 (60–70% of max HR) is known as the fat-burning zone because fat is the primary fuel source at this moderate intensity. However, higher-intensity zones burn more total calories per minute, even though a smaller percentage comes from fat. For weight loss, total calorie expenditure matters more than fat percentage. Zone 2 has the added benefits of being sustainable for long durations and producing minimal recovery stress.

Measure your resting heart rate first thing in the morning before getting out of bed. Count your pulse for 60 seconds (or 30 seconds and multiply by 2). Alternatively, most fitness watches measure resting heart rate overnight. Normal resting HR is 60–100 bpm for adults. Well-trained athletes often have resting HR of 40–60 bpm. A resting HR consistently above 100 bpm warrants a doctor visit.

Research on elite endurance athletes shows the '80/20 rule': approximately 80% of training volume in Zone 1–2 (easy, aerobic) and 20% in Zone 4–5 (hard, high-intensity). This polarized approach produces better performance gains than spending most time in Zone 3 (moderate intensity), which is sometimes called the 'grey zone' — too hard for easy recovery, too easy for high-intensity adaptations. Most recreational athletes do too much Zone 3 and not enough Zone 2.