Most Calculators Use the Same Formula for Everyone.
This one uses yours.
The problem
Why Generic Calculators Fall Short
The standard 220 − Age formula has been the default training zone reference since the 1970s. It's simple, it's fast — and it treats a 35-year-old who runs 50 miles a week identically to a 35-year-old who hasn't exercised since college. That's not personalized training. That's a population average applied to an individual.
The problem compounds in practice: a highly fit athlete with a low resting heart rate will find that age-only zone prescriptions consistently overestimate the intensity of their "easy" efforts. They spend their supposed recovery days training at what is, for their body, a moderate aerobic load — accumulating fatigue without realizing it.
One number changes all of that: your resting heart rate. Feed it into the Karvonen formula and your zones are built around your actual cardiovascular fitness, not a population average.
The methodology
The Karvonen Formula
In 1957, Finnish physiologist Martti J. Karvonen published a study in the Annales Medicinae Experimentalis et Biologiae Fenniae showing that training zones should account for Heart Rate Reserve — the difference between your maximum and resting heart rate. Sixty-plus years later, it's still the reference method in both sports science and cardiac rehabilitation.
Max HR = 220 − Age
Heart Rate Reserve (HRR) = Max HR − Resting HR
Target HR = Resting HR + (Intensity% × HRR)
Heart Rate Reserve — the gap between your max and resting HR — is where the math gets individual. A 40-year-old with a resting HR of 45 bpm has an HRR of roughly 135 bpm. A sedentary 40-year-old with a resting HR of 75 bpm has an HRR of 105 bpm. The same 65% intensity produces completely different target heart rates for these two people — 133 bpm versus 143 bpm. That 10-bpm spread is the difference between a genuine Zone 2 aerobic effort and a Zone 3 threshold grind.
This calculator implements Karvonen's method for all five standard training zones, using 220 − Age as the maximum heart rate estimate and defaulting to 60 bpm if no resting HR is provided.
1957
Year formula published
5
Training zones calculated
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Data sent to any server
The key variable
Why Resting Heart Rate Changes Everything
Your resting heart rate is one of the most reliable fitness signals you can track without lab equipment. As you train consistently, your heart becomes more efficient — each beat pumps more blood, so fewer beats are needed at rest. Elite endurance athletes routinely measure resting HRs between 35–50 bpm. Sedentary adults average 70–80 bpm. In the Karvonen formula, that gap shifts every single zone boundary.
Tracking your resting HR over time is also one of the most honest fitness metrics there is. It doesn't care how a workout felt. It reflects what's actually changing inside your cardiovascular system — and it typically drops 1–3 bpm for every real fitness gain you make.
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Lower RHR = more accurate zones
The more fit you are, the more your zones diverge from age-only estimates. Karvonen captures this automatically.
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Recalculate every 4–6 weeks
As fitness improves and resting HR drops, your zone boundaries shift. Recalculating keeps your training calibrated.
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Measure it right
Take your resting HR first thing in the morning before getting out of bed — before caffeine, stress, or movement raise it.
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Wearables help
Modern fitness watches track overnight resting HR automatically. A 7-day average from a wearable is more reliable than a single manual measurement.
Who we are
Built by Fitness Enthusiasts
CalculateMyHeartRate is an independent fitness tool, not affiliated with any gym, sports brand, or medical institution. We're fitness enthusiasts — runners, cyclists, and data-driven trainers — who kept encountering the same frustration: training plans referenced zones without making it easy to calculate them accurately for your own body.
So we built the calculator we wanted to use ourselves. Every calculation runs entirely in your browser — no account required, no data collected, no server involved. What you type stays on your device.
The tool is free, carries no ads inside the calculator itself, and is sustained by the display advertising you may see on surrounding pages. The formula is open — you can read exactly how each zone is calculated. The science is cited. Nothing is hidden.
Every zone calculation here traces back to published research. These are the papers we used.
References
Karvonen MJ, Kentala E, Mustala O. "The effects of training on heart rate: a longitudinal study." Annales Medicinae Experimentalis et Biologiae Fenniae. 1957;35(3):307–315. PMID: 13470504.
Tanaka H, Monahan KD, Seals DR. "Age-predicted maximal heart rate revisited." Journal of the American College of Cardiology. 2001;37(1):153–156. PMID: 11153730.
Garber CE, et al. "Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults." Medicine & Science in Sports & Exercise. 2011;43(7):1334–1359. PMID: 21694556.
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Ready to Calculate Your Zones?
Enter your age — and your resting HR if you have it — and get your five personalized Karvonen training zones in seconds.