How WHOOP Calculates Your Max Heart Rate (HRmax)

WHOOP starts with the Gellish formula, 207 − 0.7 × age, rather than 220 − age. Then it does the thing no other major brand claims to do: it watches your heart rate 24 hours a day and adjusts your maximum from your own data. Every other wearable either leaves the estimate alone or waits for you to correct it.

Why the starting formula matters less here

For a 40-year-old, Gellish gives 207 − 28 = 179 bpm, one beat below Garmin's Tanaka and well below the 180 that 220 − age would give. The formulas diverge most at the ends of the range, where 220 − age is about seven beats too high at 20 and five too low at 60.

But on WHOOP the formula is a seed, not a setting. It is what the system uses before it has seen you train hard, and it is supposed to be replaced by observation.

That is genuinely better in principle. It is also worth understanding the limitation, because it is the same one that makes Garmin's auto-detection unreliable: a number learned from recorded peaks can only ever move up, and an optical sensor on a moving wrist throws artefact spikes. A single bad reading during a hard session can install a maximum you never reached.

Compare what the formulas predict for your age against what your device has decided. A gap of more than about ten beats is worth investigating rather than accepting.

Why this number drives everything on WHOOP

On a watch, a wrong HRmax shifts your zones. On WHOOP it shifts your headline metric.

Strain is a 0 to 21 score built from cardiovascular and muscular load. The cardiovascular half works by weighting the time you spend in each heart rate zone, and those zones are percentages of your maximum. Time at 80 to 90% of HRmax contributes far more than time at 50 to 60%.

So if your maximum is set eight beats too high, every session looks easier than it was. Your zones shift up, you spend less recorded time in the high bands, and your strain scores read low. Set it too low and every easy ride looks like a workout. Strain then feeds the rest of the ecosystem, so one wrong number propagates into your whole picture of how hard you have been training.

This is the general rule across every brand, and it is why the Garmin and COROS posts keep returning to the same instruction: fix the anchor before you trust anything built on it.

How to get the number right

Test it properly. Build to hard over 10 to 15 minutes, finish with an all-out 60 to 90 second effort, uphill if you can. Take the highest reading, and pair a chest strap rather than trusting the wrist at maximal intensity. Repeat within two weeks and keep the higher figure. Not for anyone with cardiac risk or new to hard training. Full protocol in finding your maximum heart rate.

Then check what your profile says, and correct it if the learned value has drifted away from what you actually recorded.

Give the system real hard efforts. A model that learns from your data cannot learn a maximum you never approach. If every session is easy, the estimate stays at whatever the formula guessed.

FAQ

What formula does WHOOP use for max heart rate? The Gellish non-linear formula, 207 − 0.7 × age, as an initial estimate, not 220 − age.

Does WHOOP update my max heart rate automatically? Yes. WHOOP says it monitors heart rate 24/7 and adjusts the estimate based on your own data.

Why does my WHOOP strain seem too low? A maximum set too high is the usual cause. Strain weights time in each zone as a percentage of your maximum, so an inflated ceiling makes every session look easier than it was.

Is 220 minus age wrong? It carries roughly ±10 to 12 bpm of individual error and is biased high for young athletes and low for older ones, which is why WHOOP, Garmin and COROS all use something else.

Should I still test my max heart rate if WHOOP learns it? Yes. A learned maximum is built from recorded peaks, and optical sensors produce artefact spikes at high intensity. A tested number is the reference you check the learned one against.

Other brands

• Garmin uses Tanaka and also auto-raises from peaks.
• COROS recommends the same Gellish formula but never auto-updates.
• Fitbit uses 220 − age with reserve-based zones.
• Apple Watch publishes no formula at all.

Sources

• WHOOP on calculating max heart rate
• WHOOP on how strain works
• WHOOP on target heart rate zones
• Gellish et al. (2007), the 207 − 0.7 × age formula

Cover photo by Alextredz, CC BY-SA 4.0, via Wikimedia Commons.