Find your 5 training heart rate zones using Karvonen or simple HRmax percentage. Free, no signup — enter age and resting HR.
Between 10 and 100.
Leave blank to use 220 − age.
Measured first thing in the morning.
Effort is slippery. A run that feels "easy" on a fresh Monday morning can feel "hard" by Thursday after a stressful week — even at the same pace. Heart rate anchors intensity to a physiological signal that responds to all of those variables: fatigue, heat, sleep, caffeine, altitude. Both the American Heart Association and the Mayo Clinic recommend heart rate as the most practical way to dial in the right intensity — especially for base aerobic training, where rate of perceived exertion (RPE) tends to overestimate how hard you're actually working.
Two formulas dominate. The simple method just takes a percentage of your maximum heart rate: Zone 2 at 65% of HRmax for a 30-year-old (HRmax ≈ 190) is roughly 124 bpm. The Karvonen method (also called Heart Rate Reserve) instead uses the range between your maximum and resting heart rate, then adds a percentage of that range back on top of your resting rate. The same 30-year-old with a resting heart rate of 60 has a reserve of 130 bpm, so Karvonen Zone 2 at 65% lands at 60 + 0.65 × 130 = ~145 bpm — about 20 bpm higher.
Karvonen is more accurate because it accounts for the fact that fitter athletes have lower resting heart rates and therefore a wider working range. If you don't know your resting heart rate, the simple method is fine and the cost is small. If you do know it, use Karvonen.
| Zone | % HRmax | % HRR | Feels like | Training purpose |
|---|---|---|---|---|
| Z1 Recovery | 50–60% | 50–60% | Very easy, chatty | Active recovery, warm-up |
| Z2 Aerobic | 60–70% | 60–70% | Easy, full conversation | Aerobic base, fat oxidation |
| Z3 Tempo | 70–80% | 70–80% | Comfortable hard | Aerobic power, marathon pace |
| Z4 Threshold | 80–90% | 80–90% | Hard, single words | Lactate threshold, 10K pace |
| Z5 VO2 Max | 90–100% | 90–100% | All-out, can't talk | VO2 max, anaerobic capacity |
One of the most replicable findings in modern endurance science is the polarized training model. Sport scientist Stephen Seiler analysed training logs from world-class endurance athletes — Norwegian cross-country skiers, Kenyan runners, elite rowers — and found a consistent pattern: roughly 80% of training volume in Zone 1–2 and only about 20% in Zones 3–5, with very little time spent in the dreaded "grey zone" of Zone 3. Seiler's polarized training research suggests that recreational athletes tend to invert this — too much moderate-hard work, not enough genuinely easy work, and not enough genuinely hard work — and plateau as a result.
The most accurate method is the cheapest one: first thing in the morning, before you get out of bed and before any caffeine, place two fingers on the underside of your wrist or on the side of your neck and count beats for a full 60 seconds. Repeat across 3 mornings and average the numbers. A typical healthy adult sits between 60–80 bpm; trained endurance athletes are often in the 40–55 bpm range. If you wear a fitness tracker overnight, use the nightly low as a faster proxy.
The 220 − age formula was originally a back-of-envelope estimate from a 1971 paper, not a validated equation. Its standard error is roughly ±10 bpm. If you regularly see heart rate values on your watch that exceed the predicted HRmax during all-out efforts — the end of a hill sprint, the finish line of a 5K — your true HRmax is higher, and you should plug the measured value into the optional override field. The zones will recalibrate.
Note: this calculator gives general training-zone estimates for healthy adults. If you have a cardiac condition, take beta blockers (which suppress heart rate), or are returning to exercise after illness, talk to a clinician before using these zones for high-intensity work.
The 220 − age formula is a useful estimate but has a standard error of roughly ±10–12 bpm — meaning your true maximum heart rate could be 10+ bpm higher or lower than predicted. The Tanaka formula (208 − 0.7 × age) is slightly more accurate for adults over 40. If your fitness watch consistently records a higher peak during all-out efforts (e.g. the end of a hill sprint or a 5K race), trust the measured value over the formula.
Karvonen (Heart Rate Reserve) uses both your maximum and resting heart rate. It accounts for the fact that fitter athletes have lower resting heart rates and therefore a larger 'working range' between rest and max. Simple percentage of HRmax ignores resting heart rate. Karvonen produces target zones that are 5–15 bpm higher than the simple method for the same percentage, and is generally considered the more accurate of the two for trained individuals.
Zone 2 (the 'fat burning' zone) does burn a higher percentage of calories from fat. But total calories burned matter more than fuel source for weight loss, and harder workouts (Zone 3–4) burn more total calories per minute. The honest answer: spend most time in Zone 2 for sustainable long sessions and base fitness, add 1–2 harder Zone 3–4 sessions per week, and pay more attention to your diet than your heart rate strap.
Measure first thing in the morning, before getting out of bed and before any caffeine. Place two fingers on your wrist or neck, count beats for a full 60 seconds, and record. Repeat for 3 mornings and average them. A fitness tracker that monitors heart rate overnight will give a more accurate number — most show your resting heart rate as the average lowest reading from the previous night.
Yes — for endurance fitness. Research from Stephen Seiler and others on elite endurance athletes (runners, cyclists, rowers, cross-country skiers) consistently shows they spend ~80% of training time in Zones 1–2 and only ~20% in Zones 3–5. Zone 2 builds mitochondrial density and improves fat oxidation, which together raise the speed/power you can sustain before lactate accumulates. Recreational athletes who train mostly in the 'grey zone' (Zone 3) tend to plateau faster.
Yes, and it's the practical way to actually apply this. A chest strap is the most accurate for high-intensity intervals; wrist-based optical sensors (Apple Watch, Garmin, Fitbit, Whoop) are accurate enough for steady Zone 2 work. Set your custom zones in the device app using the bpm values from this calculator, and use the audible/haptic 'zone alert' feature so you don't drift out of Zone 2 on uphills or out of Zone 4 on downhills.
Knowing your zones is step one. Spending 4 hours/week in Zone 2 is what changes your engine. HabitBox lets you track 'Zone 2 walk/jog 30 min' as a daily habit and watch the streak compound.
Free · Local-only data · No account required