Calculate my zones
How your maximum heart rate is estimated
Every training zone is a percentage of your maximum heart rate, so everything depends on that first number. The only way to measure it exactly is a supervised maximal exercise test, which most people will never do — so we estimate it from age, using one of three formulas.
Fox is the familiar one, published in 1971. It is easy to remember and roughly right in middle age, but it drifts at both ends of the range — it tends to overestimate for younger people and underestimate for older ones.
Tanaka, from a 2001 review of the research, is the better estimate for most adults and is noticeably more accurate over 40. At 50 the two agree closely: Fox gives 170 bpm and Tanaka 173. By 60 the gap widens to 160 against 166 — enough to shift every zone boundary.
Karvonen works differently. Rather than taking a flat percentage of maximum, it uses your heart rate reserve — the range between resting and maximum — which personalises the zones to your fitness. It needs an accurate resting heart rate, but it is the most individualised of the three.
How accurate are these estimates?
Worth being straight about this: age-based formulas describe populations, not individuals. The standard deviation on the 220 − age estimate is around 10 to 12 bpm, which means a substantial share of people sit more than 10 bpm either side of their predicted maximum. Two 40-year-olds of identical fitness can have genuinely different true maximums.
The practical consequence is that zones are guides rather than gates. If Zone 2 feels punishingly hard or suspiciously easy, trust your body over the arithmetic. Perceived effort and the talk test — can you speak in full sentences, short phrases, or not at all? — remain excellent cross-checks, and they cost nothing.
What each zone actually trains
| Zone | Intensity | What it develops |
|---|---|---|
| 1 — Recovery | 50–60% | Blood flow and recovery between hard sessions. Full conversation possible throughout. Also your warm-up and cool-down. |
| 2 — Fat burn | 60–70% | Aerobic base — capillary density, mitochondrial function, fat metabolism. The zone most endurance training should sit in. Conversation possible but takes effort. |
| 3 — Aerobic | 70–80% | Cardiovascular efficiency and stamina. Short sentences only. Comfortable enough to overuse, which is a common training mistake. |
| 4 — Threshold | 80–90% | Lactate threshold and speed endurance. A few words at a time. Sustainable for perhaps 20 to 40 minutes when trained. |
| 5 — Maximum | 90–100% | Peak power and VO₂ max. Short intervals only, no conversation. Demanding to recover from — use sparingly. |
The “fat burning zone” is widely misunderstood
Zone 2 is labelled fat burn on nearly every treadmill, and the label is half true in a way that misleads.
At lower intensities a greater proportion of the energy you use comes from fat rather than carbohydrate. That much is accurate, and it has been measured: in a study of 300 adults, the rate of fat oxidation peaked at 48% of maximal oxygen uptake — about 62% of maximal heart rate, which does land in Zone 2. But proportion is not the same as amount. A harder session burns more calories per minute, and typically more fat in absolute terms, even though fat makes up a smaller share of the total.
Measuring your resting heart rate properly
If you use the Karvonen method, the accuracy of your zones depends on this figure, so it is worth measuring carefully.
Take it immediately on waking, before you sit up. Count beats for a full minute at the wrist or neck, or read it from a fitness tracker's overnight low. Repeat across three or four mornings and take the average, since a single reading is easily thrown off by a poor night or a disturbing dream.
What the figure is most useful for is comparison with itself. Endurance training lowers heart rate over weeks and months — that is the finding Karvonen's 1957 study is built on — so a resting rate drifting down as training accumulates is the expected direction of travel.
The NHS gives a normal resting heart rate as 60 to 100 beats per minute (bpm). NHS: supraventricular tachycardia (SVT). This calculator does not compare your own reading with that range. If you are worried about your heart rate, speak to a GP.
Using zones in a real training week
The most consistently supported approach in endurance training is deceptively simple: keep the great majority of your volume easy, and make the hard sessions genuinely hard. Roughly 80 per cent in Zones 1 and 2, the remaining 20 per cent in Zones 4 and 5.
The trap is Zone 3. It feels productive, so it is easy to drift into for every session — too hard to build a proper aerobic base, too easy to drive real adaptation. Training that lives permanently in the middle tends to plateau.
For general health rather than performance, the NHS asks adults for at least 150 minutes of moderate intensity activity a week, or 75 minutes of vigorous intensity activity, plus strengthening activities on at least two days. The NHS test for moderate intensity needs no monitor at all: you can still talk, but not sing.
Frequently asked questions
Sources and further reading
- National Health Service. Physical activity guidelines for adults aged 19 to 64. NHS. nhs.uk/live-well/exercise/physical-activity-guidelines-for-adults-aged-19-to-64 — “at least 150 minutes of moderate intensity activity a week or 75 minutes of vigorous intensity activity a week”, strengthening activities “on at least 2 days a week”, and the talk test quoted above: “you can still talk, but not sing”. Checked 19 October 2026.
- Fox SM, Naughton JP, Haskell WL. Physical activity and the prevention of coronary heart disease. Annals of Clinical Research, 1971;3(6):404–432. pubmed.ncbi.nlm.nih.gov/4945367 — the origin of the 220 − age formula. Record checked 19 October 2026.
- Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. Journal of the American College of Cardiology, 2001;37(1):153–156. pubmed.ncbi.nlm.nih.gov/11153730 — the review that produced the more accurate 208 − 0.7 × age equation, and the spread around an age-based estimate. Record checked 19 October 2026.
- Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate: a longitudinal study. Annales Medicinae Experimentalis et Biologiae Fenniae, 1957;35(3):307–315. pubmed.ncbi.nlm.nih.gov/13470504 — the heart rate reserve method, and the finding that training lowers heart rate. Record checked 19 October 2026.
- Gellish RL, Goslin BR, Olson RE, et al. Longitudinal modeling of the relationship between age and maximal heart rate. Medicine & Science in Sports & Exercise, 2007;39(5):822–829. pubmed.ncbi.nlm.nih.gov/17468581 — the source of the 10 to 12 bpm standard deviation quoted above. Record checked 19 October 2026.
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance, 2010;5(3):276–291. pubmed.ncbi.nlm.nih.gov/20861519 — the evidence behind the 80/20 distribution. Record checked 19 October 2026.
- Venables MC, Achten J, Jeukendrup AE. Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study. Journal of Applied Physiology, 2005;98(1):160–167. pubmed.ncbi.nlm.nih.gov/15333616 — measured in 300 adults, the intensity at which fat oxidation peaks: 48% of maximal oxygen uptake, equivalent to about 62% of maximal heart rate. The figure quoted in the “fat burning zone” section. Record checked 19 October 2026.
- National Health Service. Supraventricular tachycardia (SVT). NHS, last reviewed 12 June 2024. nhs.uk/conditions/supraventricular-tachycardia-svt — the normal resting heart rate figure quoted above: “A normal resting heart rate is 60 to 100 beats per minute (bpm).” Checked 22 October 2026.
- National Health Service. About propranolol. NHS. nhs.uk/medicines/propranolol/about-propranolol — that propranolol is a beta blocker and “slows down your heart rate”, which is why an age-based zone estimate does not hold on one. Checked 19 October 2026.
Sources on this page were checked on 19 and 22 October 2026 by the KnowYourBody web engineer. No clinician has reviewed this page.
How to read the dates above. Checked means we opened that page and confirmed it still carries the wording quoted beside it. Record checked means we confirmed the citation against the PubMed record — authors, journal and year — but the article itself sits behind a publisher paywall and we have not re-read the full text. The dates are when a person actually opened the source; they are not bumped when a release is packaged.