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Heart Rate Zone Calculator

Enter age and resting heart rate, pick a max-HR formula and a zone method, and get max HR, reserve HR and the bpm range of all five training zones.

Which of the five zones on a running watch burns fat, which builds endurance and which trains sprinting comes down to knowing the heart-rate range of each. Enter age and, better still, a measured resting heart rate, choose from two established max-HR formulas and two zone methods, and the bpm range and intensity percentage of all five zones appear at once, ready for a training plan.

On the formulas and methods: maximum heart rate comes from either Fox (220 minus age, simple but with a wide spread) or Tanaka (208 minus 0.7 × age, more accurate); zones come from either a percentage of maximum or a percentage of heart-rate reserve (Karvonen, which folds in the resting rate and is more personal). With a resting figure to hand, the reserve method is the better choice.

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How to use

  1. Enter age and, if known, resting heart rate.
  2. Choose the max-HR formula and the zone method.
  3. Read the bpm range of each of the five zones.
  4. Use the reserve method when a resting rate is available.

How it works

How maximum heart rate is estimated

The most common maximum heart rate estimate is the Fox formula: 220 - age, giving 190 at 30. It's simple but individual error can reach +/-10-12 bpm, so this tool defaults to the lower-error Tanaka formula 208 - 0.7 x age (187 at 30), and offers the Nes formula 211 - 0.64 x age for comparison. All three are estimates; a true maximum requires a treadmill test.

Percentage method vs. heart-rate-reserve method

The percentage method multiplies maximum heart rate directly by intensity: Z2 (60-70%) is 112-131 bpm at 30 under the Tanaka convention. The heart-rate-reserve method (Karvonen) includes resting heart rate first: target = resting + intensity x (max - resting). At the same age 30 with a 60 bpm resting rate, Z2 becomes 136-149 bpm — because the base rises from 0 to your resting rate, shifting the whole range up and fitting the individual better.

What each of the five zones trains

Five zone uses: Z1 warm-up and recovery, Z2 building aerobic base and fat burning (you can talk normally while running), Z3 improving aerobic endurance, Z4 near lactate threshold (only short phrases), Z5 for interval sprints. Most daily training should stay in Z2-Z3, with Z4-Z5 one to two times a week to avoid overtraining from chronic high intensity.

Calculation basis: maximum heart rate is estimated with three published formulas (Fox, Tanaka and Nes), and the training zones are split into Z1–Z5 in 10% bands. These are population estimates with wide individual variation — not a training prescription; if you have cardiovascular disease, follow your doctor's advice.

Code example

JavaScript Five zones from the heart-rate reserve method 

function zones(age, restHr, useTanaka = true) {
  const max = useTanaka ? 208 - 0.7 * age : 220 - age;
  const reserve = max - restHr;                    // heart-rate reserve
  const pct = [0.5, 0.6, 0.7, 0.8, 0.9, 1.0];      // Z1~Z5 boundaries
  const z = [];
  for (let i = 0; i < 5; i++)
    z.push({
      lo: Math.round(restHr + reserve * pct[i]),
      hi: Math.round(restHr + reserve * pct[i + 1])
    });
  return { maxHr: max, reserve, zones: z };
}

zones(30, 60);   // Z2 ≈ 138~150 bpm (aerobic endurance)

Python The same formulas in Python 

def zones(age, rest_hr, use_tanaka=True):
    max_hr = 208 - 0.7 * age if use_tanaka else 220 - age
    reserve = max_hr - rest_hr
    pct = [0.5, 0.6, 0.7, 0.8, 0.9, 1.0]
    return max_hr, [(round(rest_hr + reserve * pct[i]),
                     round(rest_hr + reserve * pct[i + 1]))
                    for i in range(5)]

zones(30, 60)   # Z2 ≈ (138, 150)

FAQ

Which maximum-heart-rate formula is more accurate?

Overall Tanaka (208 - 0.7 x age) has less error than Fox (220 - age), so this tool defaults to it. Both are population statistics, though, and individual differences of 10+ bpm are common; for precision, do a graded treadmill test or take the final-stage rate from an all-out 5K.

What's the difference between the percentage and reserve methods?

The percentage method uses only maximum heart rate with 0 as the base; the reserve method uses resting heart rate as the base. The lower the resting rate (better aerobic fitness), the wider the gap: with a 50 bpm resting rate, the Z2 lower bound can be nearly 20 bpm above the percentage method — why the same "60%" feels completely different across people.

Which zone is the fat-burning zone?

Usually Z2, about 60-70% of maximum. Fat supplies the highest share of energy at this intensity, but "highest share" doesn't mean "most total" — at higher intensity the fat share falls while total calories burned rise. Fat loss still hinges on total expenditure and diet, not guarding a specific zone.

How do I measure resting heart rate accurately?

Only needed for the reserve method. Measure on waking in the morning before getting up: press the wrist or carotid and count 60 seconds, over 3 consecutive days, then average. With a smartwatch's sleep data, take the nightly average, not a single instantaneous minimum.

Why does the formula's zone feel too high or too low when running?

Common causes: the maximum was over- or underestimated; running heart rate is affected by temperature, dehydration, caffeine and sleep loss, running 5-10 bpm higher than usual; and optical wrist heart rate jumps during strong acceleration. Cross-calibrate with the "talk test": Z2 should allow a full sentence.

Is the formula's maximum heart rate reliable?

Good enough as a starting point for training zones, but for those with cardiovascular risk, long inactivity or on medication, don't jump to intensity by formula. Consult a doctor for an exercise prescription, with a cardiopulmonary exercise test if needed.

Does medication affect heart-rate zones?

Yes. Beta-blockers and similar drugs significantly lower heart rate, so a formula zone would have you at a lower actual intensity; conversely pseudoephedrine in cold medicines and thyroid drugs may raise it. While on medication, follow the doctor's advice and how you feel.

Are my age and heart-rate data recorded?

Not uploaded. Maximum heart rate and zone computation are fully in the browser, and the server can't receive them. If history is on, it's written only to local localStorage and clearable; incognito mode clears on close.