Karvonen Calculator: Heart Rate Reserve Zones · Free

Karvonen Heart Rate Reserve Calculator

The Karvonen formula sets zones from your heart-rate reserve: maximum minus resting heart rate. Target = intensity% × (HRmax − RHR) + RHR. With a max of 185 and resting of 50 bpm (reserve 135), 70% gives 0.70 × 135 + 50 ≈ 145 bpm. The zones follow your fitness.

Zone	Range	What it trains
Z1	Recovery 118–131 bpm	Active recovery and warm-up; promotes blood flow without adding fatigue. Very easy, RPE 1–2. Full conversation, barely breathing hard.
Z2	Endurance 131–145 bpm	Aerobic base, fat oxidation and capillary density, the bread-and-butter zone. Comfortable, RPE 3–4. Can hold full sentences.
Z3	Tempo 145–158 bpm	Aerobic capacity and muscular endurance; 'moderately hard' steady work. Working, RPE 5–6. Short sentences only.
Z4	Threshold 158–172 bpm	Lactate threshold, your sustainable race-pace ceiling. Hard, RPE 7–8. A few words at a time.
Z5	VO₂max 172–185 bpm	Maximal aerobic power and VO₂max via short, hard intervals. Very hard to maximal, RPE 9–10. No talking.

Recovery

118–131 bpm

Endurance

131–145 bpm

Tempo

145–158 bpm

Threshold

158–172 bpm

VO₂max

172–185 bpm

What heart-rate reserve adds

Heart-rate reserve (HRR) is maximum minus resting heart rate. The Karvonen method, from Finnish physiologist Martti Karvonen, scales each zone within that reserve: target HR = intensity% × (HRmax − RHR) + RHR. A fit athlete with a low resting heart rate gets lower, more appropriate targets than %HRmax.

Measuring resting heart rate correctly

Measure it on waking, before sitting up and before caffeine, averaged over several days. A 5-bpm error shifts every Karvonen zone. A creeping morning rate is an early sign of fatigue or illness.

Karvonen vs %HRmax

Karvonen zones sit higher in bpm than %HRmax zones because resting heart rate raises the floor of every band. Karvonen is more individual, %HRmax is simpler. A lactate-threshold test beats both.

Worked example

Max 185 bpm, resting 50 bpm → heart-rate reserve = 135 bpm:

Zone 2, Endurance (60–70%)	131–145 bpm
Zone 3, Tempo (70–80%)	145–158 bpm
Zone 4, Threshold (80–90%)	158–172 bpm

The floors sit higher than %HRmax. That is the resting heart rate.

Frequently asked questions

Is the Karvonen formula better than percentage of max?

For most people, yes. The Karvonen formula includes resting heart rate, so a well-trained athlete with a low resting rate gets more appropriate targets. It is still an estimate. A lactate-threshold test is more individual still.

What is heart-rate reserve?

Heart-rate reserve is your maximum heart rate minus your resting heart rate. If your maximum is 185 and resting is 50, your reserve is 135 bpm. Karvonen scales each zone within this reserve.

When should I measure resting heart rate?

Measure resting heart rate immediately on waking, lying still, before caffeine, and average several mornings. A rising morning rate often signals fatigue, poor sleep or illness.

Sources

Karvonen, Kentala & Mustala (1957). “The effects of training on heart rate.” Annales Medicinae Experimentalis et Biologiae Fenniae 35:307–315.
Joe Friel, The Cyclist's / Triathlete's Training Bible. LTHR field-test protocol and %LTHR zone definitions.