Heart Rate Zones, Explained
After reading this you can turn your age or a measured maximum heart rate into five training zones, choose between the simple percentage method and the Karvonen method, and read the numbers without over-trusting them.
What heart rate zones are
Your heart rate during exercise rises with effort. A zone is a band of heart rates that corresponds to a rough range of physiological effort, from easy recovery to near-maximal work. The five-zone model splits the range between rest and maximum into labelled bands so you can aim your training at a target intensity instead of guessing.
Here is the hook. Suppose two runners both set out to run "at 70 percent". Runner A is 30 years old with a resting heart rate of 60 bpm. Runner B is 30 with a resting heart rate of 45 bpm. Using a plain percentage of maximum, both aim for the same target near 131 bpm. Using the Karvonen method, which accounts for resting heart rate, Runner A aims for 147 bpm and Runner B for 142 bpm. Same label, different numbers. The rest of this article explains why.
When to use zones, and when not to
Zones are useful when you want to control effort over minutes to hours: keeping an easy run easy, holding a steady tempo, or pacing intervals. They are a reasonable proxy for effort because heart rate tracks oxygen demand fairly closely once you are past the first minute or two.
Zones are a poor guide for short, sharp efforts. Heart rate lags. In a 15-second sprint your heart rate barely moves while your effort is maximal, so a monitor tells you almost nothing useful in that window. Heart rate also drifts upward in heat and dehydration at the same pace, a phenomenon called cardiac drift, so a fixed target can mislead you late in a long session.
The single largest error in most zone charts is the estimated maximum. The common age formulas carry a standard deviation of about \pm 10 bpm. For a 30-year-old that is roughly the width of one whole zone. If your zones feel wrong, suspect the max before you blame yourself.
The formulas and the intuition
First you need a maximum heart rate. If you have not measured it, an age formula estimates it. The classic version is simple arithmetic:
Here HR_{max} is the estimated maximum in beats per minute and age is your age in years. The classic formula is easy to remember but overestimates for younger adults and underestimates for older adults. The Tanaka formula fits large datasets better:
The two agree near age 40 and diverge from there. At age 20 the classic gives 200 and Tanaka gives 194. At age 60 the classic gives 160 and Tanaka gives 166.
Once you have a maximum, the percentage method sets each zone boundary as a fraction of it:
where p is the intensity fraction, for example 0.70 for 70 percent. This is the method most watches use by default.
The Karvonen method works from your heart rate reserve, the gap between rest and maximum, instead of from the maximum alone:
Here HR_{rest} is your resting heart rate. The term (HR_{max} - HR_{rest}) is your reserve. The intuition: at rest your effort is zero even though your heart is beating, so effort should be measured from rest upward, not from zero. A fit person with a low resting heart rate has a wider reserve, and Karvonen stretches their zones to match it.
A worked example with the demo numbers
Age 30, Tanaka max, 60 bpm rest
These are the tool's default inputs. Follow along and your numbers should match.
- Estimate the maximum with Tanaka: 208 - 0.7 \times 30 = 208 - 21 = 187 bpm.
- Percentage method, zone 3 lower bound at 70 percent: 0.70 \times 187 = 130.9, so about
131bpm. - Karvonen method, same 70 percent. Reserve is 187 - 60 = 127 bpm. Target is 60 + 0.70 \times 127 = 60 + 88.9 = 148.9, so about
149bpm.
The gap between 131 and 149 at the same 70 percent label is the whole point of Karvonen. Because your resting heart rate of 60 is well above zero, measuring from rest pushes the target up by 18 bpm.
| Zone | Intensity | % of max (bpm) | Karvonen (bpm) | Typical use |
|---|---|---|---|---|
| 1 | 50 to 60% | 94 to 112 | 124 to 136 | Recovery |
| 2 | 60 to 70% | 112 to 131 | 136 to 149 | Easy endurance |
| 3 | 70 to 80% | 131 to 150 | 149 to 162 | Tempo |
| 4 | 80 to 90% | 150 to 168 | 162 to 174 | Threshold |
| 5 | 90 to 100% | 168 to 187 | 174 to 187 | Maximal |
Reading and interpreting your results
Treat the boundaries as soft. A one or two beat difference between zones means nothing given the \pm 10 bpm uncertainty in the max. What matters is the pattern: most of your weekly training should sit low, in zones 1 and 2, with smaller amounts in zones 4 and 5. This is the well-documented distribution seen in trained endurance athletes, often summarised as spending roughly 80 percent of time easy.
Match the zone to the session, not the session to the zone. An easy run should feel easy and your heart rate should confirm it, not force it. If your zone 2 ceiling says 131 but a conversational pace puts you at 140, your estimated max is probably too low.
The most honest check is a field test. After a good warm-up, run hard for three minutes, jog easy for three, then run all-out for three more. The highest reading you see is a solid lower bound on your true maximum, and usually far better than any age formula.
See how resting heart rate reshapes the zones
Common mistakes
Several errors recur, and each has a size you can check.
- Trusting the age formula as exact
- Two people the same age can have maxima 20 bpm apart. Using one shared number treats a wide distribution as a point.
- Confusing the two methods
- Reading a Karvonen target off a percentage chart, or the reverse. For the demo numbers that is an
18bpm error at 70 percent. - Measuring resting heart rate wrong
- Resting means truly resting, taken lying down before you get up. A value measured while sitting at your desk after coffee can read 10 to 15 bpm high, which then inflates every Karvonen zone.
- Chasing zones on short intervals
- Heart rate lags effort by 30 to 60 seconds. On a 40-second interval, the number you see reflects the effort you just finished, not the one you are in.
Related tools
Once your zones tell you how hard to run, you often want to know how fast that is and what it predicts for a race. The Running Pace Calculator converts pace, speed and distance and estimates race times, which pairs naturally with holding a tempo or threshold zone.
Frequently asked questions
Which max formula should I use, 220 minus age or Tanaka?
Tanaka fits population data better across ages, so it is the sensible default. The classic 220 - age is fine to remember but overestimates the max for people under 40. At age 25 the classic gives 195 and Tanaka gives 190.5. A measured value beats both.
Is Karvonen better than the percentage method?
Karvonen personalises the zones to your reserve, so for someone with an unusual resting heart rate it is more representative of true effort. If your resting heart rate is average (near 60 to 70 bpm), the two methods are close in the middle zones and the choice matters little.
How do I find my real maximum heart rate?
A supervised graded test in a lab is most accurate. A hard field test, done when you are healthy and fully warmed up, gives a good practical lower bound. Never push to exhaustion to chase a number if you have any health concern.
Why is my watch showing a different zone than this chart?
Watches often use a different max, a different method (percentage versus reserve), or your own logged data. Check which max and which method your device uses before comparing.
Are these numbers medical advice?
No. They are an educational estimate. For any decision about your health or safety while exercising, consult a qualified professional.
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