How to Find Your Heart Rate Zones

Heart-rate zones are the cleanest way to prescribe cardio intensity without relying on subjective effort. Knowing that Zone 2 is a different animal from Zone 4 lets you build a training week where easy days are actually easy and hard days are actually hard. Beginners usually push their easy runs too hard, which makes the hard days mediocre; using zones corrects that. The math is approximate — max heart rate varies by 10+ beats person to person — but even rough zones are better than running by feel alone. This guide covers the 220-age estimate, the more accurate Karvonen method, what happens physiologically in each zone, the lactate thresholds that anchor the system, and how to assign zones to your training days.

Max heart rate

Zones are all percentages of max HR (or HR reserve), so the first job is estimating max.

Fox & Haskell (1971):   HRmax = 220 - age
Tanaka et al (2001):    HRmax = 208 - 0.7 * age
Gellish et al (2007):   HRmax = 207 - 0.7 * age

For a 40-year-old:
220-age:  180 bpm
Tanaka:   180 bpm
Gellish:  179 bpm

The 220-age formula overestimates for younger adults and underestimates for older. Tanaka is slightly more accurate. All formulas have a standard error of ~10 bpm — your actual max could be anywhere in that range.

Measuring max for real

The most accurate approach is a field test. After a thorough warm-up:

Running:  4-min all-out effort, then 3-min easy, then 3-min all-out.
          Peak HR during the last minute of the second effort is close to max.

Cycling:  20-min all-out time trial. Peak HR at the end is often 5 bpm below max.

Treadmill ramp: increase gradient 1% per minute until failure. HR at failure = max.

These tests hurt. Don’t do them cold, and don’t do them if you have unscreened cardiovascular risk factors. An exercise stress test with a clinician is the safe version.

Resting heart rate

Measure first thing in the morning, before getting out of bed, before coffee. Average across 3–5 days.

Sedentary adult:     60-80 bpm
Recreational athlete: 55-65 bpm
Trained endurance:    40-55 bpm
Elite:               30-45 bpm

Resting HR is a rough measure of fitness. Dropping 5–10 bpm over months of training is a good sign. Suddenly higher resting HR (10+ bpm above baseline) suggests fatigue, illness, or overtraining.

Percentage of max (simple zones)

Zone 1  50-60% HRmax   Active recovery, warmup
Zone 2  60-70% HRmax   Aerobic base, fat burning
Zone 3  70-80% HRmax   Tempo, aerobic power
Zone 4  80-90% HRmax   Threshold / lactate
Zone 5  90-100% HRmax  VO2max, short intervals

Example for HRmax 180:

Zone 1  90-108 bpm
Zone 2  108-126 bpm
Zone 3  126-144 bpm
Zone 4  144-162 bpm
Zone 5  162-180 bpm

Karvonen method (HR reserve)

The percentage-of-max approach ignores your resting HR, which varies a lot across fitness levels. The Karvonen formula uses HR reserve (HRR), which is more personalized.

HRR = HRmax - HRrest
Target HR = (HRR * intensity%) + HRrest

For HRmax 180, HRrest 50, 70% intensity:
HRR = 130
Target = 130 * 0.70 + 50 = 141 bpm

Karvonen zones typically hit higher HR numbers than plain percentage-of-max for trained athletes, and they track effort more accurately.

What happens physiologically in each zone

Zone 1 (50–60% HRmax). Walking briskly, warming up. Blood is moving, joints are loosening. Sustainable indefinitely.

Zone 2 (60–70%). Aerobic base. You can hold a full conversation. Primary fuel: fat. Builds mitochondria and capillary density. The zone endurance athletes spend 70–80% of their training in.

Zone 3 (70–80%). Tempo. Conversation becomes short sentences. Fuel mix shifts toward carbs. The “gray zone” beginners usually run in and should avoid — too hard to recover, too easy to drive peak adaptations.

Zone 4 (80–90%). Threshold. You can only say a couple of words. Lactate starts accumulating near your capacity to clear it. Threshold intervals improve sustainable race pace.

Zone 5 (90–100%). VO2max. Full breathing, no talking. Intervals 1–5 minutes long. Builds peak oxygen delivery.

Lactate thresholds (LT1 and LT2)

More precise than HR zones. Zones are a proxy; thresholds are the underlying physiology.

LT1 (first lactate threshold, ~60–70% HRmax) is the border between pure aerobic and mixed metabolism. Easy-day pace should stay below LT1.

LT2 (second lactate threshold, ~85–92% HRmax) is the point where lactate accumulates faster than clearance. It’s the fastest pace you can hold for roughly an hour. Threshold intervals live just above LT2.

Lab testing measures these precisely. Field estimates: LT2 HR is usually within a few beats of your average HR for a 60-minute race effort.

Training prescriptions by zone

Weekly distribution for a typical endurance athlete:
Zone 1-2  80%  (easy, long)
Zone 3    5%   (deliberately minimized)
Zone 4    10%  (threshold intervals)
Zone 5    5%   (VO2max intervals)

“Polarized training” — mostly very easy, a little very hard, almost nothing in between — outperforms “threshold training” (mostly Zone 3) in most endurance studies. Beginners tend to do the opposite and plateau.

Heart-rate drift

HR drifts up during long steady efforts even at constant pace. Causes: dehydration, heat, fatigue. A run that starts at 150 bpm and ends at 160 bpm at the same pace means your effort is actually climbing. In Zone 2 training, prioritize holding HR constant — that may mean slowing down in the second half.

Monitors and accuracy

Chest straps read the electrical signal and are the reference standard for accuracy.

Wrist optical sensors use LEDs to detect blood flow — good at steady efforts, poor during intervals and weight training where the wrist moves or tenses. Can be off by 20+ bpm during weightlifting.

If zone training matters to you, wear a chest strap at least for interval and threshold work.

Common mistakes

Trusting 220-age as gospel. Standard error ~10 bpm. Plan to refine with a field test.

Running all easy runs at Zone 3. Too hard to recover, not hard enough to trigger the peak adaptations. Keep Zone 2 boring.

Using HRmax-based zones with a high resting HR. Switch to Karvonen; the numbers will actually match the effort.

Ignoring HR drift on long runs. Constant pace with rising HR means rising effort. Let pace adjust.

Wrist HR for intervals. Optical sensors lag and misread in hard efforts. Chest strap for intervals.

Only training in Zone 4. Burns out quickly, skips the aerobic base. Most of your time should be easier, not harder.

Using the same zones after gaining fitness. Resting HR drops and LT2 shifts. Reassess zones every 3–6 months.

Run the numbers

Plug in age and resting HR into the heart rate zone calculator for Karvonen zones in bpm. Convert pace at each zone with the running pace calculator, and check session caloric burn with the calorie calculator when matching training load to nutrition.