Heart Rate Zone Calculator
Calculate your personalised heart rate training zones using the Karvonen heart rate reserve method, which factors in resting heart rate to give zones that actually reflect your cardiovascular fitness. Used by coaches and endurance athletes to keep aerobic, threshold, and VO2-max sessions in the right intensity bands.
About this calculator
The Karvonen formula computes target heart rate by adding a percentage of your heart rate reserve (HRR) to your resting heart rate: Target HR = resting HR + (max HR − resting HR) × intensity fraction. Max HR is estimated as 220 − age (the original Fox/Haskell estimate, ±10–12 bpm at the individual level) or 208 − 0.7 × age (Tanaka et al., 2001, slightly more accurate especially for older adults). The five training zones, expressed as fraction of HRR: Zone 1 recovery 0.50–0.60 (light, conversational), Zone 2 aerobic base 0.60–0.70 (easy conversation possible), Zone 3 tempo 0.70–0.80 (broken sentences only), Zone 4 lactate threshold 0.80–0.90 (one-word answers), Zone 5 VO2 max 0.90–1.00 (no talking, sustainable only for minutes). The Karvonen approach is more individualised than simple percent-of-max-HR formulas because it accounts for the variation in resting HR (typically 40–55 bpm for trained endurance athletes vs 60–80 bpm for sedentary adults). A well-trained athlete with a 45 bpm resting HR has a wider HRR than someone the same age with a 70 bpm resting, and their zone bpm targets are correspondingly wider apart. Edge cases: the 220 − age formula has a standard deviation of ±10–12 bpm at the individual level, meaning your real max HR could be 175 bpm when the formula says 190 — for any zone-based training that matters, use a measured max HR from a treadmill VO2-max test, an all-out 5-min interval, or a hard race. Beta blockers and other heart-rate-modulating medications make all formulas unreliable; use RPE or power (cycling) instead. Heart-rate drift is real: at constant pace in heat, HR climbs 5–10 bpm per hour after the first 30 minutes, which can push you out of intended zone if you chase exact numbers. And different sports produce different max HRs (cycling max is typically 5–10 bpm lower than running max for the same person), so zones derived from one sport do not transfer perfectly to another.
How to use
Example 1 — 30-year-old, resting HR 60 bpm, targeting Zone 2 aerobic base. Max HR: 220 − 30 = 190 bpm. HRR: 190 − 60 = 130 bpm. Zone 2 (60–70% HRR) lower bound: 60 + 130 × 0.60 = 60 + 78 = 138 bpm. Upper bound: 60 + 130 × 0.70 = 60 + 91 = 151 bpm. ✓ Zone 2 range: 138–151 bpm. Long easy runs, recovery rides, and base-building work all live in this band; if you can hold a full conversation, you are in it. Example 2 — 50-year-old endurance athlete, resting HR 45 bpm, targeting Zone 5 VO2-max intervals. Max HR (Tanaka, more accurate for older athletes): 208 − 0.7 × 50 = 208 − 35 = 173 bpm. HRR: 173 − 45 = 128 bpm. Zone 5 (90–100% HRR) lower bound: 45 + 128 × 0.90 = 45 + 115 = 160 bpm. Upper bound: 45 + 128 × 1.00 = 45 + 128 = 173 bpm (= max HR). ✓ Zone 5 range: 160–173 bpm. Use this for 4×4 min VO2-max intervals: surge into the zone in the first 90 seconds, hold the rest of the interval, recover 3 min at 110–130 bpm before the next rep. Total VO2-max time-in-zone per session: aim for 16–24 minutes, no more than twice per week.
Frequently asked questions
Why is the Karvonen formula better than just using a percentage of max HR?
The percentage-of-max-HR method treats two people with the same age as having identical training zones, which is wrong for anyone whose fitness differs from average. A well-trained 35-year-old with a 45 bpm resting HR has a heart rate reserve of 140 bpm; an untrained 35-year-old with a 75 bpm resting HR has a reserve of 110 bpm. At "70% of max HR" both score the same target — 130 bpm — but for the trained athlete that intensity sits in easy aerobic territory while for the untrained person it requires a hard effort. The Karvonen method anchors zones to HRR (max minus resting), which scales with both fitness and ageing, producing targets that match actual physiological strain. Validation studies against direct measurement of lactate threshold and VO2 max (Wilmore & Costill; Swain et al., 1994) show Karvonen-derived zones correlate more closely with intended training stimuli than max-HR percentages, especially for trained endurance athletes.
How accurate is the 220 − age formula for max HR?
The 220 − age estimate (Fox & Haskell, 1971) is the most cited but has a standard deviation of roughly ±10–12 bpm at the individual level — meaning roughly two-thirds of people's true max HR is within 12 bpm of the predicted value, and one-third is further off. Tanaka et al. (2001) proposed 208 − 0.7 × age as a slightly more accurate equation, especially for adults over 40 where the linear 220 − age formula systematically overestimates by ~5 bpm. Both are population-level estimates and can be wildly wrong for any single individual — some 40-year-olds have a measured max HR of 200 bpm, others 165. If zone training matters to you (interval programming, threshold work, race pacing), measure your real max HR via a graded VO2 max test, an all-out 3–5 min hard interval at the end of a warmed-up workout, or the highest HR you have seen during a race. Then use your measured max in the Karvonen formula instead of the age-based estimate; everything downstream becomes meaningfully more accurate.
What does each heart-rate zone actually train?
Zone 1 (50–60% HRR) is active recovery — used for the day after hard sessions to promote blood flow without adding training load. Zone 2 (60–70% HRR) builds aerobic base, mitochondrial density, and fat-burning capacity; the foundation of endurance, where elite athletes spend ~80% of training time. Zone 3 (70–80% HRR) is "tempo" or sweet-spot territory — useful in moderation but the famous "junk miles" trap if it crowds out both easier and harder work. Zone 4 (80–90% HRR) targets lactate threshold, raising the pace at which lactate accumulates faster than the body can clear it — directly correlates with race pace for events from 20 min to 2 hours. Zone 5 (90–100% HRR) maxes out cardiac output and VO2 max, producing the largest gains in maximum aerobic capacity but recoverable only in small doses (2 sessions per week max). The classic polarised model: 80% Zone 2, 20% Zone 4–5, near zero Zone 3. The pyramidal model: most time Zone 2, moderate Zone 3, smaller Zone 4–5. Both beat threshold-only training for endurance development.
What are the most common mistakes people make with heart-rate training?
Using the age-predicted max HR uncritically without measuring real max — this miscalibrates every zone and the cascading errors compound. Training too much in Zone 3 ("moderately hard all the time") — feels productive but produces less aerobic gain than easier Zone 2 and less anaerobic gain than harder Zone 4–5. Ignoring cardiac drift, where HR rises 5–10 bpm per hour at constant pace in heat — chasing exact zone numbers can push you to ease the pace inappropriately during a steady-state session. Using HR zones for short intervals — for anything under 90 seconds, HR lags too far behind effort to be a useful guide; use perceived exertion, pace, or power instead. Forgetting that beta blockers, thyroid medication, dehydration, sleep deprivation, and stress all alter heart-rate response by 5–15 bpm — your HR-zone targets shift when these factors change. And taking a single resting HR measurement (often inflated by morning caffeine or stress) as gospel — measure first thing in the morning before getting out of bed, over 5–7 consecutive days, and use the average.
When should I not use this calculator?
Skip it if you are on beta blockers or other heart-rate-modifying medication — your heart-rate response to exercise is artificially suppressed, and any HR-based zone target is unreliable. Use RPE (rate of perceived exertion on a 1–10 scale) or power output (cycling) instead. Skip it if you have an arrhythmia (atrial fibrillation, frequent ectopic beats, etc.) — instantaneous HR readings become noise rather than signal. Avoid it for very short or very high-intensity intervals (under 90 seconds), where HR lags too far behind effort to provide useful feedback; pace, power, or RPE work better. Do not use age-predicted zones for serious endurance training — measure your real max HR in a hard interval or test, otherwise everything downstream is off. Skip it during illness, significant under-recovery, or in extreme heat — your HR response is distorted by factors other than fitness. And do not use it as the only training metric — combine HR with pace (running), power (cycling), and RPE, since each captures a different aspect of effort and a divergence between them often reveals dehydration, glycogen depletion, or accumulated fatigue.