Heart Rate Zone Calculator

Heart-rate training zones split the gap between your resting and maximum heart rate into five intensity bands. Each band targets a different physiological adaptation: Z1 for recovery, Z2 for aerobic base, Z3 for tempo / muscular endurance, Z4 for lactate threshold, and Z5 for VO₂max ceiling.

Polarized training research (Seiler et al.) shows that elite endurance athletes spend ~80% of training time in Z1–Z2 and ~20% in Z4–Z5, with very little Z3 — the so-called '80/20 rule'. Most amateurs invert this, drifting into Z3 'grey zone' and limiting both aerobic base and high-end ceiling.

Knowing your zones requires accurate max HR. Field-testing (a maximal ~5-min hill effort followed by a sprint) is more accurate than any age-based formula, but the formulas below are good enough for programming if you don't have lab data.

Tanaka (208 − 0.7 × age, 2001): meta-analysis of 351 studies. Most accurate for adults 20–80, especially over age 40 where the older Fox/Haskell formula systematically underpredicts.

Fox / Haskell (220 − age, 1971): the original textbook formula. Easy to remember but has a standard deviation of ±10–12 bpm against true measured max — error compounds at the extremes (under 25 and over 50).

Gulati (206 − 0.88 × age, 2010): derived specifically for women on stress-test data; predicts a lower max than 220−age. Use this for women if Tanaka feels too high.

If you have a measured max HR from a lab test, race, or all-out interval session, use it directly — formula error dwarfs the accuracy difference between formulas.

Two ways to set zone boundaries from a chosen intensity (e.g. 70%):

% max HR — multiply maxHR by the intensity. Simple but ignores resting HR. A fitter athlete with a low resting HR will find zones harder than predicted.

Karvonen (heart-rate reserve, HRR) — target = ((maxHR − restingHR) × intensity) + restingHR. Anchors zones to BOTH ceiling and floor, so a fit athlete with rest HR 45 gets harder zones than someone at rest HR 70 even at the same age. Karvonen is the modern default and is enabled here.

Worked example for a 35-year-old male (Tanaka maxHR 184, resting 60): Z2 (60–70% intensity) lands at 60% × (184−60) + 60 = 134 bpm to 147 bpm under Karvonen, vs 110–129 bpm under plain %max. Karvonen pushes Z2 ~25 bpm higher because it accounts for the elevated resting baseline.

Don't change formulas mid-block. Stick with one (Tanaka recommended) so your zone boundaries stay stable across weeks of training data.

Recheck your resting HR every 4–6 weeks. As aerobic fitness improves, resting HR typically drops 3–10 bpm — Karvonen zones shift accordingly.

Heart rate lags effort by 30–90 seconds. For short intervals (under 2 minutes) use rate of perceived exertion (RPE) or power, not HR.

Heat, dehydration, caffeine, and poor sleep all push HR up at the same effort — expect Z2 to feel like Z3 on a hot day. Adjust pace, not zone target.

If your watch shows you in Z5 during a recovery run, your max HR is set too low. Field-test or move from Fox to Tanaka.