How Heart Rate Zones Work
This calculator maps five training zones from your age, resting HR, or measured max HR. Zone 1 is recovery; Zone 2 is aerobic base; Zone 3 is moderate steady state; Zone 4 is threshold; Zone 5 is VO2 and neuromuscular work. Boundaries shift depending on whether you use the simple 220 − age formula, Karvonen heart rate reserve, or a lab-tested max HR.
Garmin and COROS ship with preset zone percentages that may not match your physiology. If easy runs feel too hard in Zone 2 or tempo work never reaches Zone 4, re-check your max HR and consider lactate threshold testing instead of accepting factory defaults.
Which Method Should You Use?
Standard (220 − age): Fast estimate for beginners. Error can be ±10–15 bpm versus true max HR.
Karvonen (HRR): Accounts for resting HR — better for athletes with low resting HR or high fitness for age.
Measured max HR: Best when you have a recent max-HR field test or lab result. Re-test every 1–2 years.
What to Do in Each Zone
Zones are only useful when tied to session type. After calculating your ranges above, match each zone to a concrete workout:
- Zone 1 (Recovery): 20–40 min shuffle after hard races or between double sessions. HR should feel effortless.
- Zone 2 (Aerobic base): Majority of weekly volume — easy runs, long run bulk. If HR drifts into zone 3 on flat terrain, slow down.
- Zone 3 (Moderate): Steady runs, marathon-pace segments on tired legs. Useful but easy to overuse — caps at 10–15% of weekly time for most runners.
- Zone 4 (Threshold): Tempo blocks, cruise intervals (2–3 × 10–15 min). Sustainable "comfortably hard" — not 5K race effort.
- Zone 5 (VO2+): Short intervals (3–5 min reps) with full recovery. Neuromuscular and VO2 stimulus — 1 session per week max for most athletes.
Accuracy & Limitations
Wrist optical sensors lag during intervals and cold starts. Zone boundaries are ranges, not single numbers — a 5 bpm buffer on easy days prevents gray-zone drift. Read our Zone 2 vs Zone 3 guide for how to apply zones in weekly training.
FAQ
Why does my watch show a different Zone 2 than this calculator?
Watches often use LTHR-based zones or custom percentages. Align your watch settings with the method you trust, not whichever number appears first.
Should I use LTHR instead of max HR?
If you have a reliable threshold test, LTHR-based zones usually track training intent better than 220 − age. See Zone 2: LTHR vs Max HR.