If you need an accurate number, it should be measured manually. Some sports clinics can do this; measuring true VO2 Max, as well as actual max heart rate.
I've heard that estimate before (80% would be ~150bpm for me). But then the physiological effects described by the GP don't seem right as I need to go much higher to feel anything like "my lungs burning" (maybe 190+?)
https://www.cdc.gov/physicalactivity/basics/measuring/heartr...