Heart Rate Zone Calculator

Zone 1 (50-60% of max) is recovery -- warm-up, cool-down, easy days. Zone 2 (60-70%) is the aerobic base zone most endurance training plans build around, since it develops fat oxidation and heart efficiency with low fatigue cost. Zone 3 (70-80%) is tempo work. Zone 4 (80-90%) is threshold, near where lactate starts accumulating faster than it clears. Zone 5 (90-100%) is maximal effort, meant for short intervals used sparingly.

The default zones here are a straight percentage of your estimated maximum heart rate. Karvonen zones use Heart Rate Reserve instead -- max heart rate minus resting heart rate -- so they're personalized to your resting rate rather than max alone. Karvonen numbers come out higher than percentage-of-max zones at the same nominal intensity; neither method is wrong, but mixing them mid-program will make your zones inconsistent.

Only if it comes from a real supervised graded exercise test. If you enter a number that's at or below your resting heart rate (a common typo), the calculator ignores it and falls back to the Tanaka age estimate rather than producing negative or inverted zones. Age-based estimates carry a standard deviation of roughly 10-12 bpm, so your real max could reasonably be about 20 bpm off in either direction -- worth knowing if you're training close to your zone boundaries.

It burns a higher percentage of its calories from fat, which is where the name comes from, but it also burns fewer total calories per minute than harder zones. For actual fat loss, total calorie deficit matters more than which zone supplied the energy, so a longer or harder session can still do more overall even though a smaller share of it came from fat. Zone 2's real value is that it's sustainable and builds aerobic base, not the fat-burning label itself.

Not as your main training diet. This calculator's own guidance treats Zone 5 as sparing -- short intervals, used once a week at most -- because it's only sustainable in brief bursts and carries the highest fatigue and injury cost. Most structured plans put the bulk of weekly volume in Zone 2, with Zone 3 and 4 sessions layered in once or twice a week for tempo and threshold work.