Heart Rate Reserve Calculator

The simple way to set training zones is to take 220 minus your age and work out percentages of that number. It is quick, and it is also blunt: two people of the same age can have resting heart rates of 45 and 75, and treating them identically throws away real information about fitness.

The heart rate reserve method, often credited to Karvonen, fixes this. It starts from the same estimated maximum, subtracts your resting heart rate to get the reserve, then applies the percentage to the reserve and adds resting back. The practical effect is that a fitter person with a low resting rate gets higher absolute numbers for the same effort — which is right, because their heart already does more work per beat.

All the usual warnings apply to percentages of an estimated maximum. The 220-minus-age formula is a population average with a standard deviation of ten to twelve beats, so your true maximum could easily be fifteen beats away in either direction. Maximum heart rate is also largely genetic and does not improve with training, unlike resting rate, which falls as fitness rises. For anything more than casual use, a field test or a lab test beats any formula.

How to use the zones in practice: zone 1 and 2 for easy days, long runs and recovery, which should make up the large majority of your training time; zone 3 for steady aerobic work; zone 4 for tempo and threshold intervals that push the point at which lactate accumulates; zone 5 for short, hard repetitions. The single most common training error is spending almost every session in zone 3 — hard enough to tire you out, not hard enough to force adaptation, and too hard to recover from quickly. Keep the easy genuinely easy so the hard can be genuinely hard.

Two caveats. Heart rate lags effort by thirty seconds or more, so it is a poor guide for short intervals. And heat, caffeine, illness and medication all move it, so compare your numbers against your own recent trend rather than against a table. This is general information, not medical advice.

This calculator returns estimates for general information only. It is not medical advice, diagnosis or treatment, and it cannot replace an assessment by a qualified health professional. Individual results vary, and figures such as calorie needs, body-fat percentage and heart-rate zones are approximations based on population averages rather than measurements of you.