Target Heart Rate Calculator — Karvonen, %Max, MAF and Polarised

Why Resting Heart Rate Changes the Answer

Most target heart rate advice uses a percentage of maximum: "train at 70% of max HR". That method ignores the bottom of your range, and the bottom of your range is where fitness shows up.

The Karvonen method works from heart rate reserve instead — the span between resting and maximum:

Target = resting HR + (intensity% × (max HR − resting HR))

Two 30-year-olds with the same estimated max of 190 but resting rates of 50 and 70 get genuinely different targets for the same intensity. At 70%: 148 bpm for the fitter one, 154 for the other. Percentage-of-max gives both 133, which is too easy for one and roughly right for neither.

The Max HR Estimate Is the Weak Link

Every method here depends on a maximum, and unless you have tested it, that maximum is a guess. The familiar 220 − age carries a standard deviation of about ±10–12 bpm, which propagates straight into every zone boundary. Tanaka's 208 − 0.7 × age fits better across age ranges, especially over 40.

If your zones matter, test rather than estimate — or anchor to lactate threshold heart rate, which is both measurable and more physiologically meaningful than a maximum you have never seen.

Four Methods, Different Purposes

Karvonen (HRR) — the default for structured zone training.

Percentage of max — simpler, and still what most gym equipment and public health guidance uses.

MAF 180 (Maffetone) — 180 − age, adjusted for health and training history, as a hard aerobic ceiling. Built for athletes who habitually train too hard in the middle.

Polarised — not a zone formula but a distribution: roughly 80% of sessions comfortably below threshold and 20% genuinely hard, with the middle deliberately avoided. See how elite endurance athletes actually distribute intensity.

Zone 2 Is Not a Single Number

The most common practical error is treating "zone 2" as a fixed bpm. It is a physiological state — below the first lactate threshold — and its heart rate moves with heat, fatigue, hydration, altitude and caffeine. Two athletes on the same zone 2 target can be one undertrained and one overreaching. Use the number to start the session, and perceived effort and breathing to keep it honest.