The fat-burning zone is about 60–70% of your max HR. At this moderate intensity the largest share of calories comes from fat. However, higher-intensity work burns more total calories — and more total fat — so combine both for the best results.

Not on its own. Total calories burned and your overall calorie deficit matter most. The fat-burning zone is comfortable and sustainable, but adding higher-intensity sessions burns more calories in less time. A mix works best.

This calculator uses the Tanaka formula — 208 − (0.7 × age) — which is more accurate across ages than the old '220 − age' rule. Your maximum heart rate (max HR) is the basis for all the training zones.

Zones are percentage bands of your max HR, each linked to a training effect: very light recovery, fat-burning/aerobic base, aerobic fitness, anaerobic threshold, and maximum effort. Training in the right zone makes each workout more purposeful.

The Karvonen method personalises zones using your resting heart rate as well as your max HR, giving target = ((max HR − resting HR) × %) + resting HR. If you enter your resting heart rate, the calculator uses this more accurate method.

Use a chest-strap monitor or fitness watch for continuous readings, or pause and count your pulse for 15 seconds and multiply by four. Chest straps are the most accurate for interval training.