Heart Rate Zone Calculator

Generic 220-minus-age max heart rate gives you a rough ceiling, but it ignores your resting heart rate — and resting HR is the single most important variable for picking training intensities that actually match your fitness. Two people with the same max HR but different resting HRs need different zone targets.

The Karvonen method (heart rate reserve) uses both numbers and computes zones as percentages of the difference between max and resting HR, added back to resting. The result is zones that move with your fitness — as your resting HR drops with training, your zones automatically recalibrate to stay challenging. The calculator gives you all five standard zones (recovery, endurance, tempo, threshold, VO2 max) with target BPM ranges.

More accurate than age-based estimates for planning intervals, long runs, or zone-2 base training. Still not a substitute for a lab-tested max HR or lactate threshold test if you're training seriously.

The Karvonen method came out of mid-20th-century cardiology research, when physiologists noticed that percent-of-max-HR zones overestimated effort for fit individuals and underestimated it for unfit ones. The fix was to anchor zones in heart rate reserve (HRR), the gap between max HR and resting HR, rather than max HR alone. Zone target = resting HR + (intensity fraction × HRR). For a person with 50 resting and 190 max, HRR is 140; zone 2 (60-70% HRR) lands at 50 + 0.6 × 140 to 50 + 0.7 × 140 = 134-148 bpm. Same person at 65% of max-HR-only would target 0.65 × 190 = 124 bpm — significantly lower, which would put them in recovery rather than aerobic-base territory.

Worked example for a 40-year-old recreational runner with 55 resting HR. Estimated max via 220-age = 180 (approximate; real max could be 165 or 200). HRR = 125. The five Karvonen zones: zone 1 (50-60% HRR) = 117-130 bpm (active recovery), zone 2 (60-70%) = 130-143 bpm (aerobic base), zone 3 (70-80%) = 143-155 bpm (tempo), zone 4 (80-90%) = 155-167 bpm (threshold), zone 5 (90-100%) = 167-180 bpm (VO2 max). A typical week for a runner targeting half-marathon training: 80% of weekly volume in zone 2, 10% in zone 4, occasional zone 5 work. The numbers above tell you the BPM ranges to actually train within.

The calculator's main limit is the 220-minus-age estimate of max HR. Standard deviation is roughly ±12 bpm in studies, so for any individual, the true max could be 12+ bpm higher or lower than the formula. A field test is the best practical alternative: warm up thoroughly, then do hill repeats or all-out intervals with a chest-strap monitor (wrist-based optical HR is unreliable at high effort). The peak number you see in the last interval is approximately your real max. Or pay for a graded exercise test if you're training seriously.

Resting HR matters more than people realize and has its own measurement traps. Take it first thing in the morning, before getting up, before caffeine. Multiple-day average smooths out night-to-night variation. Resting HR drops with training (5-15 bpm over months of consistent endurance work in untrained individuals), and that drop automatically recalibrates your zones. If you stop training, your resting HR climbs back up, your HRR shrinks, and your zones contract — which is biologically appropriate but psychologically frustrating.