“Your max heart rate is 220 minus your age” is the most-repeated fitness rule of thumb there is — and it’s a reasonable starting point, but it’s also incomplete on its own. Two 30-year-olds with the same estimated max heart rate can have very different actual fitness levels, and a flat percentage of max heart rate doesn’t capture that. Our Target Heart Rate Zone Calculator uses the Karvonen formula instead, which factors in your resting heart rate too.
The Karvonen formula
Rather than taking a flat percentage of your max heart rate, Karvonen first computes your “heart rate reserve” — the gap between your max heart rate and your resting heart rate — and applies the target percentage to that reserve, then adds your resting heart rate back in:
Target HR = ((Max HR − Resting HR) × intensity%) + Resting HRThis matters because resting heart rate is a reasonable proxy for cardiovascular fitness — a well-conditioned endurance athlete might have a resting heart rate in the 40s, while a sedentary person of the same age might sit in the 70s or 80s. Using heart rate reserve instead of a flat max-HR percentage gives each person a training zone calibrated to their own starting point, not just their age.
A worked example
For a 30-year-old with a 65 bpm resting heart rate: estimated max HR is 220 − 30 = 190 bpm, giving a heart rate reserve of 190 − 65 = 125 bpm. The five zones work out to:
- Very light (50–60%): 128–140 bpm
- Light / fat burn (60–70%): 140–153 bpm
- Moderate / cardio (70–80%): 153–165 bpm
- Hard / aerobic (80–90%): 165–178 bpm
- Maximum effort (90–100%): 178–190 bpm
What these zones are useful for
Lower zones are generally associated with building aerobic base fitness and burning a higher percentage of fat as fuel per minute of exercise (though total calories burned tends to be higher at higher intensities). Higher zones build cardiovascular capacity and speed, but are harder to sustain and take longer to recover from — most structured training plans mix zones deliberately based on specific training goals, rather than always training at the same intensity.
A caveat worth taking seriously
“220 minus age” is a population average, not a measured value — actual max heart rate varies by roughly ±10-15 bpm between individuals of the same age. If you have a known heart condition, are new to structured exercise, or take medication that affects heart rate (like beta-blockers), talk to a doctor before relying on these formula-based zones, since they can be meaningfully inaccurate in those situations.
Try it yourself: Target Heart Rate Zone Calculator.