Heart Rate Zones

Overview

A heart rate zone is a range of beats per minute that corresponds to an effort. Working them out takes two numbers you already have or can measure in a minute: your age, and your resting heart rate.

Step one: estimate your maximum

The number most people have heard is 220 minus your age. It is easy to remember and it is not very good. It was never derived from a controlled study, and it drifts badly at both ends of the age range.

The better estimate:

Maximum heart rate = 208 − (0.7 × age)

At 30 years old: 208 − (0.7 × 30) = 208 − 21 = 187 bpm.

Both formulas are estimates of a population average. Individual maximums vary around the prediction by roughly ten beats per minute either way, and some people sit further out than that. If you have ever seen a genuinely maximal number on a chest strap, use that instead.

Step two: subtract your resting heart rate

Your heart rate does not start at zero. It starts wherever it sits when you are doing nothing, so the range you actually train across is the gap between the two. That gap is your heart rate reserve.

Heart rate reserve = maximum − resting

With a resting heart rate of 60: 187 − 60 = 127 bpm of reserve.

Measure resting properly. Sitting still for five minutes, or first thing in the morning before you get up. A reading taken after coffee and a flight of stairs is not a resting heart rate.

Step three: take a percentage of the reserve, then add resting back

This is the Karvonen method, and the last step is the one people skip.

Target = resting + (reserve × intensity)

A flat percentage of maximum ignores where you start. At 60 percent, the two methods differ by well over ten beats per minute for most people, which is the difference between an easy aerobic effort and one that is not easy at all.

At 70 percent, with a reserve of 127 and a resting rate of 60:

60 + (127 × 0.70) = 60 + 88.9 = 149 bpm

The five zones

Percentages are of heart rate reserve, not of maximum. The table below is worked for a 30 year old with a resting heart rate of 60.

Most endurance work belongs in zones 1 and 2, and most people spend too much time in zone 3, where the effort costs more than easy work and delivers less than hard work.

Work it out: the [heart rate zone calculator](/tools/heart-rate) runs these three steps with your own age and resting heart rate, and shows every line of the arithmetic.

How much to trust it

The zones are a guide, not a boundary. Heart rate lags effort by a minute or two at the start of a session, rises through a long one at the same pace, and climbs in heat, at altitude, when you are ill and when you are short of sleep.

If the number and the effort disagree, trust the effort. A zone 2 session is one you could hold a conversation through. If the watch says 135 and you cannot speak in sentences, you are not in zone 2 whatever the watch says.

Common questions

Is 220 minus age wrong?

It is a rough average with a wide spread, and it under-predicts for older adults in particular. 208 − 0.7 × age fits the data better, but it is still an estimate.

Why not just use percent of maximum?

Because it ignores your resting rate, and two people with the same maximum and different resting rates are not training at the same intensity at the same number of beats.

What if my resting heart rate changes?

It should, if training is working. Recalculate every couple of months. A resting rate drifting up over a week or two is one of the more reliable signs you are under-recovered.