5-zone training plan from age and resting heart rate.
| Zone | Intensity | Target range |
|---|---|---|
HR max from 220 − age (Fox formula). Real HR max varies ±10 bpm; a field test gives a personalised number.
A hard workout that does not raise your heart rate enough is a wasted hour, and an easy workout pushed too high becomes another hard one — making the next session worse. Endurance athletes have understood this for decades: the dose-response curve of cardiovascular training is dominated not by total time on feet but by time spent in the right zone. A coach watching a runner's pulse rather than her stopwatch can prescribe a session that hits the targeted physiological adaptation — fat oxidation in zone two, lactate threshold in zone four, VO₂ max in zone five — without any guesswork about pace. The five-zone heart-rate framework, popularised by Joe Friel's training textbooks and adopted by Garmin, Polar, Strava, TrainingPeaks, and most coaching platforms, gives a percentage band for each zone keyed off either the maximum heart rate (HR max) or the heart-rate reserve (HRR, also known as the Karvonen method). This calculator computes both and presents the same five zones side by side, so a runner can pick the framework that matches her existing training plan and read off the bpm range for each zone in one click.
HR max is estimated from the Fox formula: HR max = 220 − age. The Tanaka refinement (208 − 0.7 × age) is slightly more accurate for older athletes but gives essentially the same numbers up to age fifty; this calculator uses Fox for simplicity. HR reserve (HRR) = HR max − resting HR. Karvonen target = resting HR + (HRR × intensity %), which produces a bpm number that scales with the athlete's actual cardiovascular fitness. Percent of HR max target = HR max × intensity %, simpler but less personalised. The five zones use these intensity bands: Zone 1 (Recovery) 50–60 %, Zone 2 (Endurance) 60–70 %, Zone 3 (Aerobic) 70–80 %, Zone 4 (Threshold) 80–90 %, Zone 5 (VO₂ max) 90–100 %. The Karvonen method gives noticeably different numbers from the percent-of-max method for fit athletes with low resting heart rates: a runner with HR max 188 and resting HR 50 has an HRR of 138, so 70 % of HRR is 50 + 0.7 × 138 = 146.6 bpm, while 70 % of HR max is 131.6 bpm — a 15-bpm gap on the same percentage. The Karvonen method tracks training intensity better in fit individuals because their HR max stays approximately constant while their resting HR drops with training; using percent of HR max underestimates intensity for fit athletes.
Three inputs: age (in years), resting heart rate (taken first thing in the morning before getting out of bed, ideally averaged over a week to smooth out daily variation), and a method toggle (Karvonen vs percent of HR max). Defaults are 35 years and 62 bpm resting, the Karvonen method. The result panel shows HR max, HR reserve, and a five-row table of zones with the bpm range computed under the selected method. Tag this number to a chest strap or optical wrist sensor in your training watch and you can hold the right zone live during a workout — most watches let you set zone alerts that buzz when you drift out of the targeted band.
A 35-year-old runner with resting HR 62: HR max = 220 − 35 = 185 bpm; HRR = 185 − 62 = 123 bpm. Karvonen method zones: Z1 = 62 + (0.50–0.60) × 123 = 124 to 136 bpm. Z2 = 62 + 0.60–0.70 × 123 = 136 to 148. Z3 = 148 to 161. Z4 = 161 to 173. Z5 = 173 to 185. Percent of HR max zones: Z1 = 92 to 111 bpm. Z2 = 111 to 130. Z3 = 130 to 148. Z4 = 148 to 167. Z5 = 167 to 185. The Karvonen Z2 (136–148) is roughly the percent-of-max Z3 — a runner training "easy" at 70 % of HR max may actually be working at the Karvonen Z2/Z3 boundary, harder than intended. Most modern coaching defaults to Karvonen for trained athletes. Now consider a sedentary 50-year-old with resting HR 78: HR max = 170, HRR = 92. Karvonen Z2 = 78 + 0.60–0.70 × 92 = 133 to 143 bpm. Percent of HR max Z2 = 102 to 119. The same person at the same effort is in different zones depending on the framework — the Karvonen number is the more honest one for tracking actual cardiovascular work.
First, trusting 220 − age as an exact HR max. The standard error of the formula is about 10–12 bpm, which means a third of people have a true HR max more than 10 bpm away from the predicted value. Athletes whose target zone calculations drift from real-world experience should run a max-HR field test (a 6-minute all-out hill repeat at the end of a hard session usually pulls within 5 bpm of true max). Second, taking resting HR after waking but during sympathetic spikes (alarm, anxiety dream, full bladder). The cleanest measurement is sustained — a five-minute average from a wearable while still in bed gives a far more reliable number than a single radial-pulse count. Third, holding zones across temperature, hydration, and altitude. Heart rate runs 5 to 15 bpm higher in heat for the same effort, similarly higher when dehydrated, and 10 to 20 bpm higher at altitude. Use the same zones but accept that effort feels harder, or recalibrate by perceived exertion. Fourth, equating zone 4 with "hard." Zone 4 is sustainable for 20 to 40 minutes; zone 5 for 1 to 6 minutes. Going to zone 5 for an hour is not training, it is failure. Fifth, ignoring HR drift. Heart rate creeps upward by 5 to 10 bpm over a long aerobic session at constant pace as core temperature rises ("cardiovascular drift"); rebound by holding effort and accepting the climb, not by slowing down to keep HR fixed.
Five-zone systems are the dominant convention but not the only one. Three-zone polarised training (popularised by Stephen Seiler's research on elite endurance athletes) groups everything below threshold into one big easy zone, threshold itself into a thin middle zone, and everything above into a hard zone — and prescribes 80 % of training in the easy zone, 0 to 5 % in the middle, and 15 to 20 % in the hard zone. The five-zone math is the same, just bucketed differently. Power-based training in cycling has largely supplanted heart-rate zones for serious cyclists because power is instantaneous while heart rate lags; runners are catching up via running power meters. Lactate threshold can be measured directly with finger-prick testing during a graded exercise test, giving a more individual definition of "the boundary between zone 3 and zone 4" than any age-based formula. For most amateurs, the Karvonen-keyed five-zone calculation done in this calculator is more than enough — the bottleneck is execution (actually staying in zone 2 for the easy session) rather than precision of the band edges.