How the zones work
Your estimated maximum heart rate is about 220 − age. Training zones are percentages of that max (or, more accurately, of your heart-rate reserve if you enter your resting pulse — the Karvonen method):
- Zone 1 (50–60%) — very light, warm-up and recovery.
- Zone 2 (60–70%) — "fat-burning"/endurance; easy conversational pace.
- Zone 3 (70–80%) — aerobic; builds cardio fitness.
- Zone 4 (80–90%) — hard; improves speed and threshold.
- Zone 5 (90–100%) — max effort, short bursts.
Which zone should you train in?
Most of your training should sit in Zone 2 (easy and sustainable), with occasional harder Zone 4–5 intervals. The "fat-burning zone" burns a higher percentage of fat but fewer total calories than harder work — both have their place.
Limitations
The 220-minus-age formula is a population-level estimate from decades-old research and can be off by 10–20 beats for any individual — the Karvonen method (using your resting heart rate) is more personalised, but a lab-measured max heart rate is the only way to know your true number precisely.