Calculate your Heart Rate

I remember the first time I used a Heart Rate monitor in a Spinning class.

Finally I’d be able to work at the intensity the instructor wanted me to be at, all I had to do was set my age and voila the watch would tell me when I was the Target Hear Rate (THR) for recovery, aerobic anaerobic, and when I was at the red line zones.

Recovery Zone:  60% to 70%
Aerobic Zone: 70% to 80%
Anaerobic Zone: 80% to 90%
Red Line Zone : 90% to 100%

However as I started to dig into what heart rate was all about , and when I became a Spinning Instructor I found that wonderful watch was using an inferior and incorrect method which is 220 – age = maximum heart rate (MHR 100%), and to calculate your zones you would multiple the MHR by ..50, 60, .70 … .90.

So for me that would mean my MHR is 165 bpm (beats per minute)

Recovery Zone: 99-115bpm
Aerobic Zone: 115- 132bpm
Anaerobic Zone: 132-148bpm
Red Line Zone : 148-165bpm

So why is this formula inaccurate. For one thing it doesn’t take into account the fitness level of the individual (amongst many others, including the one that the inventor even says it is wrong)

Take a 25 year person who is inactive and over weight and also take a 55 year old person who exercise regularly and is at good weight, based on the above formula, that means the 25 year old can work at a higher heart rate than the 55 year old … see where this is going.

That 25 year old who should not be working at what the age based heart rate formula says they can work at.


The fitter you are the lower your Resting Heart rate (RHR) is. If we take our inactive and over weight 25 year old their RHR will most likely be higher than the fitter 55 year old.


Okay what’s RHR and how does it affect your THR?

RHR is your heart rate at rest, the best way to find this is when you are lying down, (usually first thing in the morning but wait a few minutes after that alarm has jolted you out of sleep) for a while and are relaxed. Then either using your heart rate monitor or simply checking your pulse for 15 sec and multiply the number by 4.

For the average person a RHR should be be between 60-80 beats per minute (BPM), elite athletes can have a RHR down around 40bpm.

To me the best formula to calculate your hear rate will take into account your RHR and your age, which is the Karvonen Heart Rate formula.

THR = ((Maximum Heart Rate – Resting Heart Rate) × %Intensity) + Resting Heart Rate.

If we compare the two formulas side by side you can see the big difference for my THR zones.

THR Age Based Formula Karvonen Formula
Recovery Zone 99-115bpm 121-132bpm
Aerobic Zone 115-132bpm 132-143pm
Anaerobic Zone 132-148bpm 143-154bpm
Red Line Zone 148-165bpm 154-165bpm

Luckily there are several online sties that will calculate your heart rate using the Karvonen method if your not a math whiz like me to find out where you should really be working you heart at when you exercise or ride.

If you are not using a heart rate monitor when you exercise/train find out why you should.