It's a rough estimate that can be off by 10–12 bpm for many people. The Tanaka formula (208 − 0.7 × age) used here is more accurate across ages. The only exact way to know your max HR is a supervised maximal exercise test.

Using the Tanaka formula, max HR is about 187 bpm at 30, 180 at 40, 173 at 50 and 166 at 60. Individual variation of ±10 bpm is normal, so treat it as a guide.

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.