Heart Rate Zone Calculator
Find your personalized heart rate training zones using the Karvonen formula, which accounts for your resting heart rate and age. Ideal for runners, cyclists, and athletes structuring aerobic or threshold workouts.
About this calculator
The Karvonen formula calculates target heart rate (THR) by working with your heart rate reserve (HRR) rather than just your maximum heart rate. Heart rate reserve is the difference between your estimated maximum HR and your resting HR: HRR = (220 − age) − restingHR. Your target heart rate for any zone is then: THR = (HRR × intensity%) + restingHR. This approach is more individualized than simple percentage-of-max methods because it accounts for cardiovascular fitness — a well-trained athlete with a low resting HR will get a different (and more accurate) zone prescription than a sedentary person of the same age. The five zones used here range from recovery (60% HRR) through aerobic (70%), tempo (80%), threshold (85%), and VO₂ max (92.5%). Training across these zones in the right proportions develops different energy systems and improves overall endurance performance.
How to use
Example: 35-year-old runner, resting HR = 55 bpm, target zone = threshold. Step 1 – estimate max HR: 220 − 35 = 185 bpm. Step 2 – calculate HRR: 185 − 55 = 130 bpm. Step 3 – apply threshold intensity (85%): 130 × 0.85 = 110.5. Step 4 – add resting HR: 110.5 + 55 = 165.5, rounded to 166 bpm. So this athlete should aim for approximately 166 bpm during threshold intervals. Repeating these steps for each zone gives a complete training zone profile personalized to their fitness level.
Frequently asked questions
What is the Karvonen formula and how is it different from simple max heart rate percentage?
The Karvonen formula calculates target heart rate as a percentage of your heart rate reserve (HRR), which is the gap between your maximum and resting heart rates, then adds resting HR back. Simple max-HR percentage methods ignore resting heart rate entirely, which underestimates target zones for fitter individuals with lower resting HRs. Because resting heart rate reflects cardiovascular efficiency, the Karvonen approach produces zones that are meaningfully different between a trained athlete and a beginner of the same age. This makes it the preferred method for personalizing endurance training prescriptions.
How do I measure my resting heart rate accurately for this calculator?
Measure your resting heart rate first thing in the morning before getting out of bed, as physical activity and digestion elevate HR throughout the day. Use a finger on your wrist or neck pulse, count beats for 60 seconds, or use a heart rate monitor for greater accuracy. Take the measurement on three consecutive days and average the results for the most reliable figure. A typical adult resting HR is 60–100 bpm, while trained endurance athletes often fall between 40–60 bpm.
Why should I train in different heart rate zones instead of always going hard?
Different heart rate zones stress different energy systems: lower zones (recovery, aerobic) build mitochondrial density and fat oxidation, while higher zones (threshold, VO₂ max) improve lactate clearance and cardiovascular capacity. Training exclusively at high intensities leads to accumulated fatigue, increased injury risk, and diminishing returns because your aerobic base never fully develops. Polarized and pyramidal training models — which emphasize spending the majority of time in lower zones — consistently show strong performance outcomes in research on endurance athletes. Structured zone training helps you get faster while staying healthier over the long term.