Heart Rate Calculator

How does it work?

Max HR comes from the classic formula 220 − age. Each of the training zones is a percentage of that max HR.

If you also enter your resting HR, we switch to the Karvonen method, where the zone equals rest + (max − rest) × percentage. It lands closer to reality because it factors in your fitness.

It's an estimate. Professional athletes should rely on an ergometric test.

A deeper guide to heart rate, formulas and training zones

Heart rate (HR) is the number of times the heart contracts per minute, usually expressed in beats per minute (bpm). It is one of the simplest and most informative biomarkers available: it reflects autonomic tone, hydration, sleep quality, fitness, emotional state and the metabolic cost of an effort. For an active adult, two values matter the most when planning training: the resting heart rate (RHR), measured immediately after waking up and before getting out of bed, and the maximum heart rate (HRmax), the highest value the heart can reach under all-out exertion. Together they define the heart rate reserve and the percentage ranges that anchor every training zone.

How heart rate is measured

Manual palpation at the radial artery (wrist) or carotid artery (neck) over 15 seconds multiplied by four gives a quick estimate, but it is poor for high intensity. Optical sensors on smartwatches and fitness bands use photoplethysmography (PPG) — green LEDs detect blood-flow changes in capillaries. PPG is good for rest and steady aerobic work but lags during sprints and intervals. A chest strap with an electrical sensor (ECG-based) remains the gold standard outside a clinic, with millisecond-level accuracy that also enables heart rate variability (HRV) analysis.

HRmax formulas: 220 minus age (Haskell/Fox), Tanaka, and Karvonen

The classic equation HRmax = 220 - age, popularised by William Haskell and Samuel Fox in 1971, is convenient but was never derived from a controlled study. It tends to overestimate HRmax in adults younger than 30 and underestimate it in adults older than 50, with a standard deviation of roughly 10-12 bpm. Despite the noise it is still printed on most gym equipment because it is easy to remember.

The Tanaka equation, published in the Journal of the American College of Cardiology in 2001 by Tanaka, Monahan and Seals, is the modern reference: HRmax = 208 - (0.7 x age). It came from a meta-analysis of 351 studies (around 18,712 subjects) plus a laboratory validation in 514 healthy adults aged 18-81. Its standard deviation is about 6-7 bpm and it is gender-neutral. For a 40-year-old, Haskell predicts 180 bpm while Tanaka predicts 180 bpm too — they coincide near age 40 — but at age 20 Tanaka returns 194 vs. Haskell's 200, and at age 65 Tanaka returns 162.5 vs. Haskell's 155.

The Karvonen method does not predict HRmax — it personalises the target zones using the heart rate reserve (HRR): Target HR = ((HRmax - RHR) x intensity%) + RHR. Because RHR is part of the equation, two people of the same age but different fitness levels get different target ranges. Karvonen tends to produce slightly higher target bpm than the straight percent-of-max method and is preferred by coaches working with endurance athletes, where a low RHR (40-50 bpm) would otherwise distort the linear method downwards.

The five training zones (Z1-Z5)

• Zone 1 (50-60% HRmax) - Active recovery. Easy walking, mobility work, cooldown. Builds capillary density and aids recovery between hard sessions.
• Zone 2 (60-70% HRmax) - Aerobic base / fat oxidation. Conversational pace. Highest absolute rate of fat-burning per minute and the foundation of every endurance program. Long runs and easy cycling live here.
• Zone 3 (70-80% HRmax) - Aerobic tempo. Comfortably hard, sustainable for ~45-60 minutes. Develops cardiac stroke volume and mitochondrial density. Talking becomes broken sentences.
• Zone 4 (80-90% HRmax) - Lactate threshold. The intensity at which blood lactate begins to accumulate faster than it is cleared. Critical for race pace in 5k/10k events. Sustainable for 20-40 minutes when trained.
• Zone 5 (90-100% HRmax) - VO2max / anaerobic. Sprint intervals of 30 seconds to 4 minutes. Pushes maximal oxygen uptake. Requires full recovery between repetitions.

Resting heart rate: what is normal

The American Heart Association defines a normal adult RHR as 60-100 bpm. Trained endurance athletes commonly fall in the 40-55 bpm range; values below 40 bpm without symptoms are usually physiological in elite athletes (athletic bradycardia) but warrant evaluation in sedentary individuals. On average, women's RHR runs 2-7 bpm higher than men's because the female heart is smaller and pumps less blood per beat, requiring slightly higher frequency. A persistent rise of 5-10 bpm above your personal baseline over consecutive mornings is a classic early sign of incomplete recovery, dehydration, illness onset or overtraining.

Applications: fat-loss, HIIT, anaerobic threshold

For fat-loss, the largest absolute fuel oxidation comes from longer sessions in Zone 2 (60-70%). The "fat-burning zone" label sometimes printed at low intensities is misleading — the percentage of energy from fat is higher at low intensity, but the total calories burned (and therefore the absolute grams of fat used) are higher at moderate intensity. For HIIT, a typical protocol alternates 30-60 seconds at 90-95% HRmax with equal or longer recovery in Zone 1. The anaerobic threshold sits at the Z3/Z4 boundary for most recreational athletes and at the upper end of Z4 for trained ones; field-testing it via a 30-minute time trial is more accurate than relying on percentages alone.

When to see a cardiologist

Seek medical evaluation if you experience any of the following: chest pain or pressure during exertion, fainting or near-fainting, palpitations that last more than a few seconds at rest, an RHR consistently above 100 bpm (tachycardia) or below 50 bpm with fatigue, shortness of breath disproportionate to the effort, or sudden inability to recover heart rate within 2 minutes after stopping moderate exercise. Adults over 40 starting a new vigorous program — especially with hypertension, diabetes, smoking history or family history of cardiovascular disease — should consider a pre-exercise medical clearance with stress testing.

FAQ

Is 220 minus age accurate? Only roughly. It can be off by 20 bpm in either direction for any single individual. Use Tanaka for a tighter estimate or run a maximal field test if you train seriously.

Does my smartwatch report a valid HRmax? Smartwatches infer HRmax from the highest reading observed, so the value improves as you do harder sessions but underestimates if you never reach all-out effort.

Can I exceed my predicted HRmax? Yes. Formulas are population averages; exceeding the prediction by 5-15 bpm during a hard sprint is normal and not dangerous in healthy adults.

Does caffeine affect heart rate? Caffeine can raise RHR by 3-10 bpm and exercise HR slightly. Standardise measurement conditions if you want to track trends.

Why is my morning RHR higher after a long flight or poor sleep? Both elevate sympathetic tone. Treat it as a recovery signal and reduce intensity.

Medical disclaimer: this content is educational and does not replace professional medical advice. Heart rate predictions are statistical estimates, not diagnostics. Before starting or significantly changing an exercise program — particularly if you have cardiovascular risk factors — consult a physician. Sources: American Heart Association (heart.org), Mayo Clinic, Tanaka H., Monahan K.D., Seals D.R. "Age-predicted maximal heart rate revisited", Journal of the American College of Cardiology 37(1):153-156, 2001.