Heart Rate Zone Calculator Widget

Add a heart rate zone calculator to your website. Visitors enter their age, and optionally their resting heart rate, and see an estimated maximum heart rate and the five training zones in beats per minute.

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<iframe src="https://a2z.tools/embed/w/heart-rate-zone-calculator" title="Heart Rate Zone Calculator by A2Z Tools" width="100%" height="740" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.

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How it works

Maximum heart rate is estimated with the Tanaka formula (208 - 0.7 x age) by default, the same choice as the A2Z Heart Rate Zone Calculator. Tanaka, Monahan and Seals derived it in 2001 from a meta-analysis of 351 studies with 18,712 subjects and confirmed it in a laboratory study, finding that the classic 220 - age underestimates maximum heart rate past 40. The classic formula can still be selected and the other one is always shown for comparison. Without a resting heart rate the zones are the five 10% bands from 50% to 100% of maximum that Polar and other heart-rate-monitor makers use. With a resting heart rate the widget switches to the Karvonen method, which applies the same percentages to heart rate reserve (maximum minus resting). The formulas come from adult data, so ages under 18 get a message instead of zones.

Calculation method

  • Max HR (Tanaka 2001) = 208 - 0.7 x age; classic = 220 - age; rounded to a whole bpm
  • Zone limits (% of max): Z1 50-60, Z2 60-70, Z3 70-80, Z4 80-90, Z5 90-100; limits rounded to whole bpm
  • Karvonen: target = resting HR + (max HR - resting HR) x intensity; resting HR must be at least 20 bpm below max

Worked examples

Age 40, no resting rate

Inputs: Age 40, Tanaka

Result: Max 180 bpm; zone 2 is 108-126 bpm, zone 4 144-162 bpm

208 - 28 = 180; 60-70% of 180 = 108-126.

Age 30, resting 60 bpm, classic formula

Inputs: Age 30, 220 - age, resting 60

Result: Max 190 bpm, reserve 130 bpm; zone 1 is 125-138 bpm (Karvonen)

60 + 130 x 0.5 = 125 and 60 + 130 x 0.6 = 138.

An estimate for general information only - not medical advice. Talk to a doctor or registered dietitian about your health.

Limitations

  • Not for under-18s, and not for anyone on rate-limiting medication or with a heart condition unless a clinician sets the zones.
  • Zone boundaries are a convention of heart-rate-monitor makers, not physiological thresholds such as lactate or ventilatory thresholds, which need testing.
  • Does not adjust for heat, altitude, dehydration or fatigue, which all raise heart rate at the same effort.

Where publishers use it

  • Running, cycling and triathlon clubs publishing training plans by zone
  • Personal trainers explaining zone 2 and interval sessions to clients
  • Fitness-watch and wearable review sites
  • Cardiac-rehab-friendly exercise guides that stress checking with a doctor

Questions

How accurate are age-based max heart rate formulas?

They describe averages; an individual's measured maximum can differ by 10 bpm or more. A supervised maximal test gives a measured value; otherwise treat the zones as a starting point and adjust by feel.

Why use Tanaka instead of 220 - age?

220 - age was never derived from a formal study, and Tanaka's analysis found it underestimates max heart rate in adults over 40, markedly so in older adults. At age 40 both give 180 bpm; at 60, Tanaka gives 166 and 220 - age gives 160.

When should I enter a resting heart rate?

When it is known, measured on waking before getting up. The Karvonen method, from a 1957 training study, then personalises the zones using heart rate reserve.

Do heart medications affect this?

Yes. Beta blockers and some other medicines lower heart rate, which makes age-based zones unsuitable. The widget recommends checking with a doctor.

Sources

  1. Age-predicted maximal heart rate revisited (Tanaka, Monahan, Seals) - Journal of the American College of Cardiology 37(1):153-156, 2001 . HRmax = 208 - 0.7 x age
  2. The science of exercise prescription: Martti Karvonen and his contributions - British Columbia Medical Journal . Heart rate reserve method; original: Karvonen, Kentala, Mustala, Ann Med Exp Biol Fenn 35:307-315 (1957)
  3. What are heart rate zones? - Polar Electro . Five zones at 50-60, 60-70, 70-80, 80-90 and 90-100% of maximum

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools Heart Rate Zone Calculator
https://a2z.tools/heart-rate-zone-calculator

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