Heart rate zones (Karvonen method)

About this calculator

Karvonen zones — heart rate reserve, not flat percentages

The Karvonen method calculates training zones as a percentage of your heart rate reserve (HRR = max HR - resting HR), not flat % of max HR. This matters because two people with the same max HR but different resting HRs need different zone targets.

The five zones

Z1 — Active recovery / fat oxidation (50-60% HRR): warmup, cooldown, very easy
Z2 — Aerobic base (60-70% HRR): the king of endurance training. Build mitochondria, develop fat metabolism, low fatigue cost
Z3 — Tempo (70-80% HRR): "comfortably hard" — sustainable for 30-90 min for fit athletes
Z4 — Threshold (80-90% HRR): lactate threshold, the edge of what's sustainable for ~1 hour
Z5 — VO2 max (90-100% HRR): intervals, 3-8 min on, equal recovery

Why two max HR formulas

Fox 220 - age is the classic but overestimates for younger athletes and underestimates for older ones. Standard error is ~12 bpm.
Tanaka 208 - 0.7×age is from a 2001 meta-analysis (Tanaka et al.) and is more accurate across age groups. Standard error is ~8 bpm.

For training zone math, use Tanaka. For wall-clock simplicity, Fox is fine.

The 80/20 rule

The current consensus on endurance training: ~80% of weekly time in Z1-Z2, ~20% in Z4-Z5. The middle zone (Z3) is a trap — too hard to recover from, too easy to drive max-power adaptation. Most amateur runners spend 60-70% of their week in Z3 and wonder why they don't improve.

FAQ

What's wrong with just using % of max HR?

It ignores resting HR. A trained athlete with a 45 bpm resting HR and a sedentary person with a 75 bpm resting HR will have very different actual exertion at, say, 70% of max HR. Karvonen using HRR fixes this — same intensity = same effort across fitness levels.

How do I find my real max HR?

A formal max test (treadmill ramp, all-out 4-min interval). Look at your highest recorded HR during a hard race or workout — that's usually within 2-3 bpm of true max. Formulas are estimates; if you have real data, use it.

Resting HR — when do I measure it?

First thing in the morning, lying in bed, before you check your phone. Take the average of 5 mornings. A wrist-worn tracker that reports 'overnight low HR' is also a good proxy. Skip the day after hard training or a high-stress evening — readings will be elevated.

Are these zones right for cycling and running?

HR zones differ slightly across modalities — cycling max HR is usually 5-10 bpm lower than running max because you're less weight-bearing. For accuracy, do a max test in each sport. For most amateurs, running zones ± 5 bpm work fine for cycling.

Age (years)	35
Resting heart rate (bpm)	58
Max HR estimator	Tanaka 208 - 0.7×age (more accurate)

Heart rate reserve (HRR)	126
Z1 lower bound (50% HRR)	121
Z2 lower bound (60% HRR)	133
Z3 lower bound (70% HRR)	146
Z4 lower bound (80% HRR)	158
Z5 lower bound (90% HRR)	171