How Polar Calculates Your Max Heart Rate (HRmax)

Polar does not measure your maximum heart rate. It estimates it with 220 − age, the oldest and least accurate formula in circulation, and builds five zones as straight percentages of that number. Garmin moved to Tanaka and COROS to Gellish. Polar, the company that put heart rate monitors on wrists in the first place, still documents the simple rule.

The formula and the zones

For a 40-year-old, 220 − 40 = 180 bpm. The five zones are clean 10-point bands of it:

• Zone 1, very light: 50 to 60% of HRmax
• Zone 2, light: 60 to 70%
• Zone 3, moderate: 70 to 80%
• Zone 4, hard: 80 to 90%
• Zone 5, maximum: 90 to 100%

That tidiness is the selling point and the weakness. The bands are easy to remember and they are identical for everyone, which means all the personalisation has to come from the one number underneath.

220 − age carries an error of roughly ±10 to 12 bpm for an individual, and it is biased: too high for young athletes and too low for older ones. At 20 it predicts 200 where Gellish predicts 193. At 60 it predicts 160 where Gellish predicts 165. Five beats at 60 moves every zone boundary by two to five beats.

Compare the formulas on your own age and you will see the spread Polar's default hides.

Where Polar is better than its default

Polar's documentation is unusually honest about this. It says outright that the most accurate way to know HRmax is to have it clinically measured, on a supervised treadmill or bike test, and that a field test is the next best thing.

More usefully, Polar lets you set HRmax per sport profile in Polar Flow, rather than once globally. That matters more than most people realise. Your running maximum usually sits several beats above your cycling maximum, because more muscle mass is doing the work. One global number makes your bike zones too hard or your run zones too easy.

How to replace the estimate

1. Test it. Build to hard over 10 to 15 minutes, finish with an all-out 60 to 90 second effort, uphill if possible, and take the highest reading. Use a chest strap. Repeat within two weeks and keep the higher number. Not for anyone with cardiac risk or new to hard training. Full protocol in finding your maximum heart rate.
2. In Polar Flow, open the sport profile you want to change and enter the tested HRmax there.
3. Repeat per sport if you train more than one, using a maximum tested in that sport.

The deeper fix

Percentage-of-maximum is a blunt system whatever number you feed it. Two athletes with identical maximums and very different fitness get identical zones, which cannot be right.

Two better anchors, both of which Polar supports:

• Heart rate reserve, which adds your resting heart rate to the picture. Polar's own Karvonen-style calculation is available in Flow, and the Karvonen calculator shows what it does to your numbers.
• Threshold heart rate, which moves with your training rather than your age. LTHR zones is the model, and LTHR vs %HRmax zones explains why the two systems disagree about where Zone 2 sits.

FAQ

What formula does Polar use for max heart rate? 220 − age by default. Polar documents it as the simple rule and recommends a lab or field test instead.

What are Polar's heart rate zones? Five zones as percentages of HRmax: 50 to 60%, 60 to 70%, 70 to 80%, 80 to 90% and 90 to 100%.

Can I set my own max heart rate on Polar? Yes, in Polar Flow, and you can set a different one for each sport profile, which is worth doing if you both run and ride.

Is Polar's max heart rate accurate? The default is an age estimate with roughly ±10 to 12 bpm of individual error. Test yours and enter it.

Does Polar update my HRmax automatically? No. Unlike Garmin, it will not quietly raise the number from a recorded peak, so a stale value stays stale until you change it.

Other brands

• Garmin uses Tanaka and auto-raises HRmax from recorded peaks.
• COROS recommends Gellish and runs three zone models.
• Apple Watch never publishes its formula at all.

Sources

• Polar on heart rate zones
• Polar on calculating max heart rate
• Polar support on heart rate zones
• Tanaka, Monahan & Seals (2001), the 208 − 0.7 × age formula
• Gellish et al. (2007), the 207 − 0.7 × age formula

Cover photo by Bill Ebbesen, public domain, via Wikimedia Commons.