Heart Rate Zones Calculator

This calculator uses your age, resting heart rate, and optional measured maximum to estimate personalized training zones via the Karvonen method. Understanding each range helps you structure endurance builds, tempo runs, recovery sessions, and high-intensity intervals while avoiding overtraining.

How the Zones Work

Zone 1 is the recovery range (50‑60% of heart rate reserve), ideal for warming up post-workout. Zone 2 (60‑70%) builds aerobic capacity and teaches the body to burn fat efficiently. Zone 3 (70‑80%) moves into tempo effort for lactate threshold development. Zone 4 (80‑90%) primes the anaerobic system, while Zone 5 (90‑100%) is reserved for short maximal bursts.

By factoring in your resting heart rate, the Karvonen formula identifies a personalized starting point for each zone, rather than relying solely on a fixed percentage of max heart rate.

Example: A 38-year-old with a resting rate of 58 bpm and a measured max of 186 bpm has a heart rate reserve of 128 bpm. Their Zone 2 range becomes 58 + 0.60×128 ≈ 135 bpm up to 58 + 0.70×128 ≈ 147 bpm. This keeps Zone 2 workouts focused on sustainable intensity without pushing into the tempo or interval zones prematurely.