Heart Rate Zones Calculator

How it works

Heart rate zones are training intensity bands defined as percentages of your heart rate reserve (HRR), which is the difference between your max heart rate and your resting heart rate. Training in different zones produces different physiological adaptations: building base aerobic fitness, improving lactate threshold, or developing peak power.

The most common zone model uses five zones. Z1 (50–60% HRR) is very light recovery work — easy walking pace, useful for warmup and cooldown. Z2 (60–70%) is the aerobic base zone — most "easy" running and long cycling rides happen here. The body learns to oxidize fat efficiently at this intensity, and high training volume in Z2 is the foundation of endurance fitness. Z3 (70–80%) is the aerobic threshold — sustainable for an hour or so, good for tempo runs. Z4 (80–90%) is the lactate threshold — the hardest pace you can hold for 30–60 minutes; key for race-pace fitness. Z5 (90–100%) is VO₂max territory — short, painful intervals that develop top-end aerobic capacity.

This calculator uses the Karvonen formula: target HR = resting HR + (max HR − resting HR) × intensity%. It's more accurate than simple percent-of-max formulas because it accounts for individual fitness — a fitter person with a lower resting HR has a wider HR reserve.

Max HR is estimated as 220 minus age, which is a population average with substantial individual variation (±10 bpm). For a precise number, do a max-HR field test or use a treadmill test with an exercise physiologist. Resting HR is best measured first thing in the morning before getting out of bed, averaged over 3–5 days.

Polarized training research (Stephen Seiler's work) suggests endurance athletes get best results from spending ~80% of training time in Z1–Z2 and ~20% in Z4–Z5, with relatively little time in Z3.