Heart Rate Zones Calculator — Max HR (4 formulas) and 5 Karvonen Training Zones

Real-world use cases

• Build your weekly easy / hard split for marathon training

  You're 12 weeks out from a marathon. Plug your age, sex, and measured morning resting HR; pick Tanaka. The calculator returns your Z2 range (e.g. 136–149 bpm for a 30-year-old male at RHR 60). Eighty percent of your weekly minutes should sit inside that band on long runs and easy days; the remaining twenty percent of weekly minutes belong to Z4 intervals near half-marathon pace. Tape the Z2 ceiling to your watch face and the easy days actually stay easy.

• Stop "junk miles" — find the Z3 trap you keep falling into

  Most amateur runners drift into Z3 (the "comfortably hard" tempo zone) on what should be easy days. Read off the Z2/Z3 boundary from the table; that's your hard ceiling for easy runs. If your average run HR is consistently above it, you're not doing easy training — you're doing chronic medium, which fatigues without building either base or peak. Drop the pace until the watch sits 5 bpm below the Z3 line, every easy run.

• Cycle indoor on Z4 intervals without a power meter

  No power meter? Set your trainer to a comfortable cadence and shift gears until your HR climbs into Z4 (80–90% HRR). Hold 4 × 8 minutes at the bottom of Z4 with 2 min easy spin between. The calculator gives you the exact bpm range so you don't guess; for a 35-year-old male Tanaka at RHR 55, that's roughly 161–174 bpm. HR lags power by 30–60 seconds, so the watch settling into the band is your signal that the effort is right.

• Compare your wearable's zones against this calculator

  Open the calculator side-by-side with your Garmin / Apple Watch / Coros zone screen. If the watch's Z2 ceiling is 5+ bpm higher than the calculator's, the watch is likely using plain %MHR with the Fox/Haskell formula. Override your watch's max HR to the Tanaka value here (or to the Gulati value if you're female) and the zones tighten up immediately. One configuration change, every workout downstream gets more accurate.

• Recovery check — RHR trend that warns of overtraining

  Resting HR rises 5–10 bpm above your normal baseline when you're under-recovered. Re-enter the calculator with today's morning RHR. If your Z2 range has shifted up noticeably (say, 5 bpm), that means your reserve has shrunk and the same subjective effort now lives in a higher zone. The fix is the same answer endurance coaches have always given: an easier day, more sleep, then re-measure tomorrow morning.

Common pitfalls

• Trusting 220 − age as your real max HR. The formula carries ±10-15 bpm error after age 40 and systematically over-estimates max HR in women by 5-8 bpm. Use Tanaka or Gulati instead, and confirm with a field test once you've trained a few months.

• Measuring resting HR right after waking up and walking to the kitchen. Walking 30 steps already pushes RHR up 8-15 bpm. Lie still for one full minute before checking — phone-based pulse readers work fine if you stay supine.

• Trying to live in the "fat-burning zone" exclusively. Z2 has the highest fat percentage of energy but lower absolute calorie burn. For weight loss the weekly calorie deficit and weekly protein matter much more than the zone split. Train Z2 for endurance gains, not as a fat-loss shortcut.

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