How to find your target heart rate
Two numbers decide everything: how fast your heart can go (max HR) and how hard you want to train, expressed as a percentage of it. Target heart rate is the second applied to the first, and the five training zones are just bands of that percentage. Type your age, move the slider, and the tool shows the bpm your watch should read.
Estimating max heart rate
The classic estimate is 220 − age, conventionally traced to Fox, Naughton and Haskell (1971): 190 bpm at 30, 170 at 50, 150 at 70. It is easy to remember and it is also the weakest link in the calculation — the equation is reported with a standard deviation of 10 to 12 bpm, and it systematically underestimates max HR in older adults, so two 40-year-olds with the same "180" can genuinely differ by 20 bpm or more.
Better options, both offered above:
- Tanaka 208 − 0.7 × age (Tanaka et al., JACC 2001). Derived from a meta-analysis of 351 studies and 18,712 people, it tracks better with age; a 45-year-old gets 176.5 bpm. (Some clinics print 207 − 0.7 × age; the original published equation is 208.)
- Gulati 206 − 0.88 × age, from 5,437 asymptomatic women. Use it only for women without known heart disease, and expect wide individual error — in validation studies it had the largest bias of the nine common equations.
A real measurement beats every formula: a supervised maximal test, a 5 km time trial or a 3-minute step test. Enter that number in Manual mode.
Percent of max vs heart-rate reserve (Karvonen)
The simple method multiplies max HR by the intensity: 70% of 190 is 133 bpm. The Karvonen method, published by Karvonen in 1957 and still the standard in exercise physiology, first subtracts resting heart rate to get the heart-rate reserve, then adds the chosen percentage of that reserve back: target = resting + % × (max − resting). Someone with a resting HR of 50 reaches 148 bpm at the same 70%. Because a trained heart sits lower at rest but still reaches a similar maximum, Karvonen produces meaningfully higher — and usually more realistic — training targets for fitter people, especially in the easy zones. Resting heart rate is normally 60 to 100 bpm in adults, measured properly on waking before coffee; endurance athletes often sit near 40.
What each zone is for
- Z1 (50–60%) — very light: warm-ups, cool-downs, recovery spins and walks. You can sing.
- Z2 (60–70%) — the aerobic base: capillary density, mitochondria, fat oxidation. Long, easy, conversational. Most endurance athletes spend the majority of their week here.
- Z3 (70–80%) — moderate, "tempo-ish". Good for aerobic power, but easy to over-use because it feels productive without being very specific.
- Z4 (80–90%) — threshold and anaerobic capacity. Intervals of 5–20 minutes that raise the pace you can hold before lactate accumulates.
- Z5 (90–100%) — VO2 max intervals of 30 seconds to 5 minutes. Highly effective in small doses, and the fastest route to overtraining in large ones.
The widely used distribution is roughly 80/20: 80% of training time easy (Z1–Z2) and 20% hard (Z4–Z5), with little time in the middle. The talk test is a free substitute for a chest strap — full sentences is Z1–Z2, short sentences is Z3, single words is Z4, no speech at all is Z5.
Which zone table is "official"? None of them
The 50/60/70/80/90 five-zone split is a consumer and coaching convention — it is what Polar's and most watches' defaults follow — rather than a publication of the American Heart Association or the American College of Sports Medicine. The published bands genuinely differ, and the tool shows them side by side for your own max HR:
- AHA: moderate-intensity activity is "about 50–70%" of maximum heart rate, vigorous is "about 70–85%".
- ACSM: bands effort by heart-rate reserve instead — roughly 40–59% HRR for moderate and 60–89% HRR for vigorous, which lands higher in bpm than the equivalent %HRmax band.
- CDC no longer publishes %HRmax target zones at all, and recommends the talk test, a perceived-exertion scale, or METs.
For health purposes, the practical takeaway is that anything in the 60–85% region counts as solid exercise; the exact edge of a zone matters far less than whether you are actually moving, and how consistently.
Things that move the number
Heart rate is a response, not a score. Caffeine, heat and humidity, dehydration, illness or a fever, altitude, poor sleep, stress and even a heavy meal can push the same pace 5–15 bpm higher, and cardiac drift means it creeps up during a long steady session at constant power. Judge effort on heart rate, breathing and perceived exertion together. Max HR is also sport-specific: cycling maximum is typically 5–10 bpm lower than running maximum, which is why a zone table from a running test reads slightly high on the bike. And if you take a beta blocker or another rate-lowering medicine, none of these formulas apply — the drug caps your heart rate, so you may never reach the calculated target; use perceived exertion instead and ask your clinician, who may recommend an exercise stress test.
Frequently asked questions
What is a normal resting heart rate?
For adults, 60 to 100 bpm is the usual range, and highly trained endurance athletes are often near 40. Measure yours properly: count your pulse for a full 60 seconds right after waking, before coffee or your phone, on three mornings and take the average. A resting rate suddenly 10 or more bpm above your normal can be an early sign of illness or overtraining.
How accurate is 220 minus age?
It is a population average with a standard deviation of about 10 to 12 bpm, and it tends to underestimate max HR in older adults. Roughly two thirds of people fall inside that band, so the number is a starting point rather than a personal measurement. The Tanaka equation (208 − 0.7 × age) tracks better with age, and a real test beats both.
Should I use percent of max or the Karvonen formula?
Use Karvonen (heart-rate reserve) if you know your resting heart rate, especially if you are fit — it usually gives more realistic targets. Percent of max is simpler and fine for general health training. The two agree at high intensity and differ most in the easy zones, where the reserve method gives higher bpm.
What is the fat-burning zone?
Roughly 60–70% of max HR, zone 2. A larger share of the calories burned there come from fat, but higher intensities burn more total calories, so the total fat burned ends up similar. The real value of zone 2 is the aerobic base it builds, not the fuel mix on the display.
Are the five heart rate zones official?
Not in the sense of a medical standard. The 50/60/70/80/90 split is the consumer and coaching convention used by most watches. The American Heart Association publishes 50–70% (moderate) and 70–85% (vigorous) of max HR, ACSM bands effort by heart-rate reserve (about 40–59% and 60–89% HRR), and the CDC no longer publishes %HRmax zones at all. The tool shows all of them for your own max HR.
How long should I stay in each zone?
For general fitness, 150 minutes a week of moderate work (Z2–Z3) plus two harder sessions is a solid baseline. Endurance athletes typically aim for 70 to 80% of total time in Z1–Z2 and 20 to 30% in Z4–Z5, keeping Z3 for specific tempo blocks.
Do medications change these zones?
Yes, and this is the biggest caveat on the page. Beta blockers and some other medicines slow the heart, so you may never reach the calculated target no matter how hard you work — the formulas simply do not apply. Switch to a perceived-exertion scale or the talk test, and ask your clinician, who may recommend an exercise stress test to measure your real target heart rate. Stop and seek help for chest pain, faintness or unusual breathlessness.
My heart rate is much higher than the formula says — what now?
Watch effort rather than the number. Chronic elevation can come from caffeine, heat, dehydration, anaemia or thyroid problems, and some people simply have a naturally high max HR. If your heart rate is unexpectedly high at rest, or you feel palpitations, chest pain or dizziness, see a doctor rather than training through it.