Calculate your Heart Rate Reserve (HRR) and all 5 personalized training heart rate zones using the Karvonen formula. Enter your age and resting heart rate to find your fat burning, aerobic, threshold, and peak zones.
✓ Verified: American College of Sports Medicine (ACSM) Exercise Guidelines — April 2026
Used to estimate max heart rateEnter your age (10-100).
Measure first thing in the morningEnter resting HR (30-120 bpm).
Tanaka is more accurate for older adults
Heart Rate Reserve
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⚠️ Disclaimer: Consult your doctor before starting any exercise program, especially if you have heart disease, hypertension, or other medical conditions. These are estimates based on population averages.
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Sources & Methodology
🛡️Karvonen formula per M.J. Karvonen et al. (1957) and ACSM Exercise Prescription Guidelines 11th Ed.
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Karvonen MJ et al. — Annals of Medicine and Experimental Biology (1957)
Original HRR and target heart rate formula publication. The Karvonen method is the gold standard for individualized exercise intensity prescription.
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American College of Sports Medicine (ACSM) — Exercise Prescription Guidelines
Official exercise intensity zone recommendations and HRR method endorsement. acsm.org
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Tanaka H et al. — Journal of American College of Cardiology (2001)
Max HR formula: 208 - 0.7 x Age. More accurate than 220-Age, particularly for older adults.
Max HR = 220 - Age (traditional) or 208 - 0.7 x Age (Tanaka)
HRR = Max HR - Resting HR
Target HR = Resting HR + (Intensity% x HRR) [Karvonen formula]
Zone range = [Low%] to [High%] of HRR
Target HR = RHR + (Intensity x HRR)
Example: Age 35, Resting HR 65, Max HR = 185, HRR = 120 bpm.
Zone 2 (60-70%): Lower = 65 + (0.60 x 120) = 137 bpm. Upper = 65 + (0.70 x 120) = 149 bpm.
Last reviewed: April 2026
How Is Heart Rate Reserve Calculated?
Heart Rate Reserve (HRR) is the difference between your maximum heart rate and your resting heart rate. It represents the working range of your cardiovascular system — the beats per minute available for exercise above your resting baseline. A trained athlete with a resting HR of 45 bpm has a much larger HRR than an untrained person with the same max HR and a resting HR of 75 bpm.
The Karvonen formula uses HRR to calculate personalized target heart rate zones. This is more accurate than simply taking a percentage of max HR, because it accounts for individual differences in resting heart rate — which varies significantly based on fitness level, age, and health status.
The 5 Heart Rate Training Zones
Zone
% of HRR
Purpose
Feel
Zone 1
50-60%
Recovery, warm-up
Very light — can hold full conversation
Zone 2
60-70%
Fat burning, aerobic base
Light — can speak in sentences
Zone 3
70-80%
Aerobic fitness, endurance
Moderate — short sentences only
Zone 4
80-90%
Lactate threshold, speed
Hard — few words at a time
Zone 5
90-100%
VO2max, peak performance
Maximum — cannot speak
💡 Zone 2 Training: Research by Dr. Iñigo San Millán and others shows that most elite endurance athletes spend 80% of their training time in Zone 2. Zone 2 builds mitochondrial density, improves fat oxidation, and builds the aerobic base needed for higher intensity work without excessive recovery time.
Karvonen vs Simple % of Max HR
For a 35-year-old with max HR 185, Zone 2 using simple % of max HR = 185 x 0.65 = 120 bpm. Using Karvonen with resting HR 65: Zone 2 = 65 + (0.65 x 120) = 143 bpm. The Karvonen method gives a 23 bpm higher target — a meaningful difference that prevents under-training. For a trained athlete with resting HR 45, Karvonen gives even higher zone targets compared to simple % method.
Frequently Asked Questions
HRR = Max HR - Resting HR. It is the working range of your cardiovascular system. A higher HRR indicates better cardiovascular fitness. Average adults: ~120 bpm HRR. Athletes: 150-180+ bpm HRR.
Target HR = Resting HR + (Intensity% x HRR). Example: Age 35, resting HR 65, Max HR 185, HRR 120. Zone 2 (65%): 65 + (0.65 x 120) = 143 bpm. More accurate than simple % of max HR.
Traditional: Max HR = 220 - Age. Tanaka (more accurate): Max HR = 208 - (0.7 x Age). For a 35-year-old: 220-35 = 185 (traditional) or 208-24.5 = 183.5 (Tanaka). Tanaka is preferred for older adults.
Zone 1 (50-60% HRR): Recovery. Zone 2 (60-70%): Fat burn/aerobic base. Zone 3 (70-80%): Aerobic. Zone 4 (80-90%): Threshold. Zone 5 (90-100%): Maximum/VO2max.
60-100 bpm is normal for adults. Athletes often have 40-60 bpm. Measure first thing in the morning before getting out of bed for the most accurate reading. Average 3 days for accuracy.
Zone 2 (60-70% HRR) burns the highest percentage of calories from fat. However, higher zones burn more total calories. For weight loss, a mix of zones is most effective. Zone 2 is important for building the aerobic base that supports all higher-intensity work.
Simple % ignores resting HR. A fit person and unfit person of the same age have the same max HR but very different resting HRs. Karvonen uses HRR (the actual working range), giving genuinely personalized training zones.
Measure first thing in the morning before getting up. Count pulse for 60 seconds at wrist or neck. Take readings 3 consecutive mornings and average them. Avoid caffeine, alcohol, or stress the night before.
Max HR = 208 - (0.7 x Age). Published in JACC 2001. More accurate than 220-Age, especially for older adults and women where 220-Age tends to overestimate true max HR.
Higher is better. Untrained adults: ~120-130 bpm HRR. Regular exercisers: ~140-150 bpm. Trained athletes: 150-180+ bpm. HRR increases mainly by lowering resting HR through regular aerobic exercise.