Key takeaways
- Use heart-rate reserve (max minus resting), not percent of max; the error is often a whole zone.
- Get max from a real maximal effort, resting from overnight wearable data; 208 minus 0.7 times age is only a placeholder.
- Validate with the talk test: full sentences in zone 2, phrases in zone 3, words in zone 4.
- Recompute every couple of months as resting heart rate falls.
The 220-minus-age formula is wrong for most individuals by ten beats or more, and percent-of-max zones built on it are wrong by more. There is a better way that needs nothing but a watch: two numbers, one subtraction, and five zones that fit your heart rather than an average one.
Why is 220 minus age wrong?
Because it was never derived from data on individuals. Tanaka, Monahan and Seals pooled 351 studies covering 18,712 people and then tested the result in a lab on 514 more; the line that fitted was 208 minus 0.7 times age, and the older formula underestimated maximum heart rate in older adults. Even the better formula is a population average with a wide spread: two healthy forty-year-olds can have true maximums thirty beats apart.
The second problem is bigger. Percent-of-max zones ignore resting heart rate, so a fit person with a resting rate of 45 gets the same zone boundaries as an unfit one with a resting rate of 75. Their hearts have very different working ranges, and the zones should reflect that.
Free tool: Two numbers from your watch give five zones that fit your heart, not an average one. Open the heart rate zone calculator →
The two numbers you need
Resting heart rate: take the lowest overnight reading your wearable reports across a normal week. Maximum heart rate: the highest sustained reading from a genuinely maximal effort in the past year, such as the last minute of a hard 5K or the top of a long hill sprint. If you have neither, 208 minus 0.7 times your age is a better starting formula than 220 minus age, and you replace it the first time you see a real maximum.
- Resting: lowest overnight value over seven nights, ignoring a night you were ill or had been drinking.
- Maximum: highest value held for 10 seconds or more during a hard effort; ignore one-second spikes, which are usually optical-sensor noise.
- Reserve: maximum minus resting. This is the number the zones are built on.
If you have never seen a true maximum, you can find one on a day you feel fresh: warm up for fifteen minutes, then run a long hill hard for two to three minutes with the last thirty seconds as fast as you can hold, and take the highest sustained reading. A race finish works too. Anyone with a heart condition, or unsure, should ask a doctor before doing this; the 208 formula is a fine placeholder in the meantime.
PeakBeat does this from your own data. Your effort writes the setlist. Join the free beta →
How to calculate heart rate zones with the Karvonen formula
Each zone boundary is resting plus a percentage of reserve. Worked example: max 188, resting 52, reserve 136.
| Zone | % of reserve | Calculation | Beats per minute |
|---|---|---|---|
| 1 Recovery | under 60% | 52 + 0.60 × 136 | below 134 |
| 2 Aerobic base | 60 to 75% | 52 + 0.75 × 136 | 134 to 154 |
| 3 Tempo | 75 to 87% | 52 + 0.87 × 136 | 154 to 170 |
| 4 Threshold | 87 to 95% | 52 + 0.95 × 136 | 170 to 181 |
| 5 Max | above 95% | above 181 |
The steps for your own numbers:
- Subtract resting from maximum to get reserve.
- Multiply reserve by the lower and upper percentage of each zone.
- Add resting back to each result.
- Round to whole beats and write them on the watch.
What is each heart rate zone for?
The boundaries only matter because each zone trains something different.
- Zone 1, recovery: blood flow without stress. Warm-ups, cool-downs and the day after a hard session.
- Zone 2, aerobic base: mitochondria, capillaries and fat oxidation. Most of the week lives here; the zone 2 guide covers how much.
- Zone 3, tempo: sustainable hard running. Useful in small doses for race preparation; the grey zone when it fills the week by accident.
- Zone 4, threshold: raises the pace you can hold before lactate accumulates. Cruise intervals and tempo runs of twenty to forty minutes.
- Zone 5, max: VO₂max intervals of two to five minutes. Small share, big recovery cost.
Three zones, easy, moderate and hard, are enough for most people. The five-zone split earns its keep once you are doing structured sessions and want to tell threshold work from VO₂max work.
Heart rate reserve vs percent of max: the size of the error
Compare the same runner's zone 2 under both methods.
| Method | Zone 2 lower bound | Zone 2 upper bound |
|---|---|---|
| Karvonen (60 to 75% of reserve) | 134 | 154 |
| Percent of max (60 to 75% of 188) | 113 | 141 |
Percent of max puts this runner's whole zone 2 inside Karvonen zone 1 and tells them that 141, a comfortable aerobic pace, is the top of easy. They will run their easy days too slow to build anything, or ignore the watch and drift into the grey zone the 80/20 research warns about. That is the size of the error, and it is larger the fitter you are.
How to check your zones with the talk test
Zone 2 should allow full sentences. Zone 3 allows short phrases. Zone 4 allows a word or two. If your calculated zone 2 does not match the talk test, your max is probably wrong; fix the max, not the formula. A max set too low makes every zone too easy; a max set too high, often from a sensor spike, makes zone 2 feel like a tempo run.
Two more checks. Heart rate should settle within a zone after a few minutes rather than climbing steadily, which indicates you are above your first threshold. And the pace you can hold in zone 2 should slowly rise over weeks, as the zone 2 guide describes; if it never moves, the boundaries are probably off.
How often should you recalculate?
Resting heart rate falls as you get fitter, which widens reserve and shifts every boundary. Recompute every couple of months, or whenever your seven-night resting average moves by more than three beats. Maximum heart rate drifts down slowly with age and does not rise with fitness, so update it only when a hard effort shows a higher sustained value than you have on record.
Day-to-day readings also move for reasons that have nothing to do with fitness. Heat, dehydration, caffeine, poor sleep and the tail end of a cold all push heart rate up at a given pace. On those days the zone is still right and the pace that lands in it is simply slower; running the usual pace and ignoring the number defeats the purpose of having zones.
Day to day, your zones do not move, but your readiness to train in them does. A low HRV reading or a poor readiness score is a reason to keep the day in zone 1 or 2, not a reason to redraw the zones.
Zones that move with you
PeakBeat computes zones by Karvonen from your watch's resting rate and your recorded max, updates them as those change, and uses them to choose music. If you prefer percent of max or fixed bands, you can choose those instead. Your bands, your thresholds, and a track that fits where your heart is right now.
Want this answered from your own data?
That is what PeakBeat does. Your effort writes the setlist. In private beta — the waitlist is free.
Questions
What if my watch's max heart rate looks too high?
Do heart rate zones change with fitness?
Are five heart rate zones necessary?
What is a good resting heart rate for calculating zones?
Is the Karvonen formula accurate?
Sources
- Karvonen M.J., Kentala E., Mustala O. (1957). The effects of training on heart rate: a longitudinal study. Ann Med Exp Biol Fenn. https://pubmed.ncbi.nlm.nih.gov/13470504/
- Tanaka H., Monahan K.D., Seals D.R. (2001). Age-predicted maximal heart rate revisited. J Am Coll Cardiol. https://www.jacc.org/doi/10.1016/S0735-1097(00)01054-8
Builds the UPeak apps and writes up the research behind them.