Target Heart Rate Calculator

The three numbers behind every zone

Maximum heart rate (MHR) is the highest rate your heart reaches in all-out exercise. It is measured properly in a cardiac stress test — treadmill intensity rising while an ECG watches for the signature of maximum — and the theoretical human ceiling is about 300 bpm. In practice it is usually estimated from age, which is also its weakness: the formulas output population averages, and individuals scatter widely around them (elite rowers in their twenties have measured anywhere from 160 to 220 bpm). Use a formula for planning; trust a test for precision.

Resting heart rate (RHR) is your rate awake, calm, and unstressed — best taken in the morning by counting a full minute of pulse. Typical adults sit around 50–90 bpm (older charts say 60–100); above the range is tachycardia, below it bradycardia — though fit athletes routinely rest in the 50s and sometimes lower, which is fitness, not a fault. Heart rate reserve is simply the gap between the two: HR_reserve = MHR − RHR (a max of 180 with a resting 68 gives a reserve of 112). The reserve is what lets a zone system see your fitness instead of only your age.

The five training zones

• Zone 1 (50–60%) — very light: warm-ups, cool-downs, recovery days.
• Zone 2 (60–70%) — light: fat burning and endurance base; effort you can hold for a long time.
• Zone 3 (70–80%) — moderate: aerobic development, speed and strength support.
• Zone 4 (80–90%) — hard: near-maximal sustainable output; builds how long you can stay near the top.
• Zone 5 (90–100%) — maximum: sustainable only briefly; sharpens muscle and cardiovascular capacity, and demands real recovery. Never train only here.

Training far above your zone wastes energy and lengthens recovery; far below it, the session does little. The zones exist so each workout lands where its benefit lives.

Three ways to turn intensity into a heart rate

Percent of maximum (used when no resting rate is entered) is the simplest: multiply MHR by the zone's percentages. A 36-year-old's MHR is 220 − 36 = 184, so a moderate 70–80% zone is 184 × 0.70 ≈ 129 to 184 × 0.80 ≈ 147 bpm. The Karvonen method (used when a resting rate is entered) applies the percentages to the reserve instead, then adds the resting rate back: for the same 36-year-old resting at 70, the reserve is 114, the 70% point is 0.70 × 114 + 70 = 150, and the 80% point is 161 — a noticeably higher, more personal zone. Perceived exertion skips percentages entirely: on the Borg 6–20 scale you rate how the work feels (the scale is built so rating × 10 roughly equals heart rate), and the target converts as THR = RHR + (MHR − RHR) × (B − 6) / 14 — a "somewhat hard" 13 for someone with max 190 and resting 60 gives 60 + 130 × 7/14 = 125 bpm. The modified Borg CR10 compresses the same idea to 0–10, with THR = RHR + (MHR − RHR) × B / 10: a "somewhat difficult" 4 gives 60 + 130 × 0.4 = 112 bpm.

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