How the heart rate zone calculator works
The Karvonen method sets zones as a percentage of your heart rate reserve, the gap between resting and maximum heart rate, then adds your resting rate back. Because it accounts for resting heart rate, it fits fit and unfit people better than simple percentages of max.
Target HR = HRrest + reserve × intensity %
HRmax ≈ 208 − 0.7 × age (Tanaka)
Zone 2 is the easy, conversational pace that builds aerobic base; zones 4 and 5 are hard efforts you can sustain only for minutes. The American Heart Association describes moderate exercise as about 50% to 70% of max heart rate and vigorous as 70% to 85%.
Worked example
A 40-year-old with a resting heart rate of 60 has an estimated max of 180 bpm and a reserve of 120. Zone 2 runs from 60 + 72 = 132 to 144 bpm. Zone 4 threshold work sits at 156 to 168 bpm, and zone 5 tops out at 180.
Frequently asked questions
How do I find my real max heart rate?
A supervised exercise test is most accurate. A field test such as a hard 3-minute uphill effort after a warm-up gives a good approximation for healthy people.
Why use Karvonen instead of % of max?
It accounts for resting heart rate, so two people with the same max but different fitness get different, more personal zones.
What is zone 2 training?
Steady, easy exercise in which you can still speak in full sentences. It builds mitochondrial and aerobic capacity with little fatigue.
Is it safe to train in zone 5?
For healthy people, short intervals are fine. Check with a doctor first if you have heart disease or symptoms.
Updated October 2026. Results are estimates for education, not financial or medical advice. All math runs in your browser; nothing you type is sent anywhere.