Karvonen and percentage-of-max heart rate zones for cardio training.
Updated
Inputs
Resting HR enables the Karvonen (HRR) zones — the column on the right of the table.
Predicted max heart rate
Tanaka (2001) — used for zones below
187 BPM
Fox (1971) — 220 − age
190 BPM
Zone
% of HRmax
Karvonen (HRR)
Zone 1 — very light
94 – 112 BPM
—
Zone 2 — light
112 – 131 BPM
—
Zone 3 — moderate
131 – 150 BPM
—
Zone 4 — hard
150 – 168 BPM
—
Zone 5 — very hard
168 – 187 BPM
—
Educational only — not medical advice. Talk to a clinician for personal health decisions.
Quick start
How to find your target heart-rate zones
Enter your age (and optionally resting HR) to see predicted max heart rate and the five ACSM training zones, both as % of max and via the Karvonen heart-rate-reserve method.
Step 1
Enter age
Sets predicted max HR via Tanaka (208 − 0.7·age) and Fox (220 − age).
Step 2
Optional: resting HR
Add your resting heart rate to enable the Karvonen (HRR) column for individually calibrated zones.
Step 3
Read the zone table
Five zones from very-light to very-hard, in BPM. Match zones to your sport's demands.
In-depth guide
Target heart rate — max HR, zones, and the Karvonen method
Heart rate is the cheapest, most universal proxy for exercise intensity. This tool predicts your max heart rate two ways, splits it into the standard ACSM training zones, and (if you supply a resting heart rate) computes the same zones via the Karvonen heart-rate-reserve formula. Match zones to your sport's demands — most aerobic base building lives in Zone 2.
Predicting your max heart rate
Two formulas dominate the literature:
Fox (1971) — HRmax = 220 − age. The one on every gym poster. Easy to remember; overestimates under 30 and underestimates over 60.
Tanaka (2001) — HRmax = 208 − 0.7·age. Re-fit on a much larger pooled dataset; tracks measured values more accurately across ages 20–80. We use this as the default.
For a 30-year-old: Fox gives 190, Tanaka 187. For a 60-year-old: Fox 160, Tanaka 166. For a precision number, do an actual max-HR field test under supervision (graded treadmill ramp). Predicted values carry roughly ±10 BPM of individual error.
The five training zones
Per ACSM Guidelines for Exercise Testing and Prescription (11th ed.):
Zone 1 (50–60% HRmax) — warm-up, cool-down, recovery walks.
Zone 2 (60–70%) — aerobic base. The workhorse zone for endurance training. Most polarised plans put 70–80% of weekly volume here.
Zone 3 (70–80%) — tempo / "grey zone". Useful for sustained tempo runs but often over-used; many programs deliberately under-emphasise Zone 3 in favour of polarised Z2 + Z4/5.
Zone 4 (80–90%) — threshold intervals, 5–20 min sustained efforts.
Zone 5 (90–100%) — VO₂ max work. Short hard intervals (1–4 min); 5–10% of weekly volume.
The Karvonen (HRR) method
Karvonen et al. (1957) defined a target heart rate using both maximum and resting heart rate:
target = (HRmax − HRrest) · intensity + HRrest
The intensity is expressed as a fraction of heart rate reserve (HRR), the gap between resting and max. Because well-trained people have lower resting heart rates, their HRR is wider and their zones shift downward in BPM for the same percent-of-HRR target. This makes the Karvonen method more individually calibrated than percent-of-max alone.
If you supply a resting HR, this calculator shows both the percent-of-max and HRR numbers for each zone so you can compare. Most modern coaching uses HRR for prescribed zones; percent-of-max is fine as a quick reference.
Measuring resting heart rate
Take it first thing in the morning, lying still in bed before getting up, after at least 4 hours of sleep. Count for 30 seconds and double, or use a chest strap / smartwatch for a few minutes. Average over 3–5 mornings — single readings vary by 5–10 BPM from sleep stage, hydration and stress.
Typical adult range: 60–80 BPM. Trained endurance athletes often run 40–55. A persistent jump of 5–10 BPM above your baseline is a useful early signal of fatigue, illness or under-recovery — track it over time.
Frequently asked questions
Is my data uploaded anywhere?
No. The heart-rate calculation runs entirely in your browser. Nothing is sent to a server, stored, or logged.
Why two max-HR formulas?
The classic 220-age (Fox 1971) is the one almost every gym poster cites, but it's a fit to a small sample and is known to overestimate max HR for younger adults and underestimate for older adults. Tanaka et al. (2001) re-fit the line on a much larger pooled dataset and gave HRmax = 208 − 0.7·age, which tracks measured max HR more accurately across the age range. We surface both numbers and use Tanaka for the zones.
What is the Karvonen method?
Heart Rate Reserve (HRR) — Karvonen et al. 1957 — calculates a target HR using both your max and your resting heart rate: target = (HRmax − HRrest) · intensity + HRrest. It scales with cardiovascular fitness because well-trained people have lower resting heart rates, which shifts each zone's BPM lower for the same effort. If you supply a resting HR, the calculator shows both the percent-of-max and the Karvonen numbers side by side.
Which zones should I train in?
Zone 2 (60–70% HRmax / 40–60% HRR) is the workhorse for aerobic base — most polarised endurance plans put 70–80% of training volume here. Zone 4–5 work is short, hard intervals — typically 10–20% of weekly volume. Zone 3 ('grey zone') is often over-used; many programs deliberately under-emphasise it. Match zones to your sport's demands; talk to a coach for personalised plans.
How do I measure my resting heart rate?
Take it first thing in the morning, lying still in bed before getting up, after at least 4 hours of sleep. Count for 30 seconds and double, or wear a chest strap or smartwatch for a few minutes. Average over 3–5 mornings — single readings vary by 5–10 BPM from sleep stage and stress. A typical adult value is 60–80 BPM; trained endurance athletes often run 40–55.
How accurate are predicted max-HR formulas?
Population-level standard error of about ±10–12 BPM for any individual — meaning your true max could easily be 10 BPM above or below the formula. For precision, do an actual max-HR field test (e.g. progressive treadmill ramp under supervision) or use lactate-threshold testing for zone-3/4 boundaries.
Is it safe to train at zone 5?
For healthy adults, brief (1–4 minute) intervals at 90–100% HRmax are a normal part of training. If you have heart disease, hypertension, or are over 40 starting a new exercise program, talk to a clinician before doing high-intensity work. Stop and seek medical attention if you experience chest pain, dizziness or unusual shortness of breath at any intensity.
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