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