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Recovery As of 2026-04-24

How Heart Rate Zone Calculator works

Methodology for the Heart Rate Zone Calculator: formulas, coefficients, data sources, assumptions, and known limitations.

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Education · Not medical advice. Output is deterministic math from your inputs.Editorial standardsSponsor disclosureCorrections

Scope

Returns five training zones using three alternative definitions: percent of max HR, the Karvonen heart-rate reserve method, and the Maffetone low-aerobic method (180 - age).

Zones are training-intensity anchors, not medical cutoffs. The right definition depends on your sport, age, and goal.

Formula

Max HR can be taken as 220 - age (Fox) or 208 - 0.7*age (Tanaka, more accurate). Karvonen: zone_hr = (MHR - RHR) * intensity + RHR. Maffetone aerobic ceiling: 180 - age, with adjustments for training history and illness.

Coefficients

Parameter Value Note
Fox MHR formula 220 - age Widely used, ~10 bpm RMSE.
Tanaka MHR formula 208 - 0.7*age Tighter RMSE, ~7 bpm across the adult range.
Zone 1 (recovery) 50–60% HRR
Zone 2 (aerobic) 60–70% HRR
Zone 3 (tempo) 70–80% HRR
Zone 4 (threshold) 80–90% HRR
Zone 5 (VO2) 90–100% HRR

Data sources

  1. Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate; a longitudinal study. Ann Med Exp Biol Fenn. 1957;35(3):307-315. — PMID 13470504. Origin of the heart-rate reserve formula.
  2. Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol. 2001;37(1):153-156. — PMID 11153730. Modern MHR regression that outperforms 220 - age across most adults.
  3. Maffetone P. The Maffetone Method: the holistic, low-stress, no-pain way to exceptional fitness. Ragged Mountain Press, 1999. — 180-age low-aerobic training ceiling used in endurance coaching; the author's own reference page documents the adjustments.
  4. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription, 11th ed. Wolters Kluwer, 2021. — Reference for the five-zone intensity scheme.

Assumptions

  • Resting heart rate is measured first thing in the morning and is not transiently elevated by caffeine, illness, or stress.
  • If a laboratory-measured max HR is available, use it instead of any age-based formula.

Approximation range

220-age: RMSE ~10–12 bpm. Tanaka 208 - 0.7*age: RMSE ~7–8 bpm.

Karvonen-derived zone boundaries sit 5–10 bpm lower than percent-of-max zones for the same intensity label — they are not interchangeable.

Limitations

  • All age-based MHR formulas are wrong for some percentage of the population; a few athletes have true MHRs 15+ bpm from the regression line.
  • Heart-rate zones are blunt for interval work: HR lags power/effort by 30–90 seconds.
  • Beta-blockers and other cardiac medications invalidate every zone in this tool.

Reproducibility

30 yo, MHR (Tanaka) = 208 - 0.7*30 = 187. RHR 60. Karvonen Z2 (60–70% HRR): (187-60)*0.6 + 60 = 136; (187-60)*0.7 + 60 = 149.

Change log

  • 2026-04-24: methodology page first published.
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  • Sweat Rate Calculator — Calculate your personal sweat rate from pre/post-exercise weigh-ins and estimate fluid and sodium losses using ACSM guidelines.
  • Sleep Debt Calculator — Track 7 nights of sleep to calculate accumulated sleep debt with a recovery timeline and quality assessment.

Worked example

Computed by the same engine bundle served at /engines/heart-rate-zone-calculator.js. Re-runnable: the values below are the literal output of compute(engineInput).

Input

tool
heart_rate_zone_calculator
age
30
resting_hr
60

Output

maxHr
190
hrr
130
zones
[{"zone":"Zone 1 (Recovery)","lowBpm":125,"highBpm":138},{"zone":"Zone 2 (Endurance)","lowBpm":138,"highBpm":151},{"zone":"Zone 3 (Tempo)","lowBpm":151,"highBpm":164},{"zone":"Zone 4 (Threshold)","lowBpm":164,"highBpm":177},{"zone":"Zone 5 (VO2 Max)","lowBpm":177,"highBpm":190}]

FAQ

Which formula is used here?
Uses max heart rate and resting heart rate reserve (Karvonen) to build five intensity zones.
Can I use metric or imperial units?
Yes. This tool supports both metric and imperial units and remembers your preference.
Is this medical advice?
No. This tool provides general fitness estimates and should not replace medical guidance.
Is this tool free and private to use?
Yes. AI Fit Hub tools are free, no-signup browser tools. Inputs stay in your browser unless you choose to share a URL.
Do these tools replace medical guidance?
No. These outputs are general fitness estimates — not medical advice.
Can I switch between metric and imperial units?
Yes. Every tool supports both systems and remembers your preference in localStorage.
General fitness estimates — not medical advice. Consult a healthcare professional for medical decisions.