Karvonen Heart Rate Calculator

The Karvonen formula works out a target heart rate from your resting heart rate as well as your age, which makes it far more personal than the plain age-based percentage method.

The key idea is Heart Rate Reserve (HRR): the span between your resting heart rate and your maximum. You train at a percentage of that reserve, added back onto your resting rate, rather than at a percentage of your maximum.

HRmax = 208 - (0.7 x Age) HRR = HRmax - Resting Heart Rate Target HR = (HRR x Intensity%) + Resting Heart Rate

For a 35-year-old with a resting HR of 60 bpm training at 70% intensity: HRmax = 184 bpm HRR = 184 - 60 = 124 bpm Target HR = (124 x 0.70) + 60 = 147 bpm

Compare that with the simple method: 184 x 0.70 = 129 bpm. An 18-bpm gap, which is more than a whole zone wide. Someone following the simple number would be training in Zone 2 while believing they were in Zone 3.

The reason for the gap is that percentage-of-max quietly assumes your resting heart rate is zero. Nobody’s is. The lower your resting rate, the bigger the error, so the method fails worst for exactly the fit people most likely to be using it.

The five standard zones:

• Zone 1 (50-60%): Recovery and light activity. Comfortable conversation pace.
• Zone 2 (60-70%): Fat burning. The aerobic base most endurance athletes build on.
• Zone 3 (70-80%): Aerobic. Breathing is harder; full sentences become short sentences.
• Zone 4 (80-90%): Threshold. Sustainable for only 20-40 minutes for most people.
• Zone 5 (90-100%): Maximum effort. Intervals, sprints, and race finishes.

Note: the 220 - age formula for HRmax is an average estimate with high individual variability. If you have had a recent maximum heart rate test, you can substitute that value for a more accurate result. Consult a healthcare provider before beginning a new exercise program.