Since we first started tracking heart rate on the iPhone back in 2010 (anyone remember the iPhone 2?), we’ve used the same default heart rate zones and calculations for maximum heart rates as our defaults – 220-Age was the maximum heart rate for anyone, and zones were cut up 10% per zone – period – the Haskell-Fox calculations. As many of you have read, we’ve always encouraged people to set their own Max HR and Zones, as these defaults were developed in the 1970s on a small study of males around their 30s – it was never meant to be used as a standard. 
When I joined the company in 2011, I read Heart Rate Training by Benson and Declan, and have ever since been trying to get people to update to more modern zones. For a variety of reasons, including insistence from company founders and general public acceptance, it stayed Haskell-Fox, but that is changing.
We are still offering Haskell-Fox as an option, just no longer making it the default.
It’s 2020, and Benson and Declan have updated their book to be the latest known to science and practice at this time. It is time for us as well to do what we can to make everyones experience, cardio development and results the best they can be right from the start.
While we still maintain that doing a personal assessment is the ultimate, our defaults will at least be the best they can be per current science.
Default Maximum Heart Rate Calculation
The new maximum heart rate default is calculated based off the formula developed at Oakland University in 2007: 
- HRmax = 192 − (0.007 × (age x age)).
The original linear equation had a confidence interval of ±5–8 bpm, while this nonlinear equation had a tighter range of ±2–5 bpm, and really helped take into account ages beyond above and below the main bell curve ages.
You can always adjust and set your Max HR to the 220-Age or any other number (hopefully a measured one that matches you perfectly) – see how to set your maximum heart rate here.
Default Heart Rate Zones Calculation
For heart rate zones, we are basing our zones and definitions per Benson and Declan’s newly updated Heart Rate Training manual, to help you maximize your training effectiveness based on your goals. 
|Zone 1||Easy / Endurance||50-60%||Aerobic|
|Zone 3||Stamina||75-85%||Aerobic (borderline Anaerobic)|
 Heart Rate Training, Roy Benson & Declan Connolly, November 26, 2019, pp. 5