I recently got a Fitbit Charge 2. Pretty neat device, however I have some concern regarding its accuracy. So maybe someone here can relay their experience or maybe link to an article that can expand my knowledge on the question.

What I can give an internet source (aka calculator):

Age
Height
Weight
Exercise (6 Mile Walk, Flat Land, 3 MPH Speed)

What I can give the Fitbit device:

Age
Height
Weight
Exercise (6 Mile Walk, Flat Land, 3 MPH Speed)
Stride (if required)
Heart Rate


As you can see the primary difference between the two is the physical device I can actually adjust my stride if I want and more importantly it can monitor my heart rate. What concerns me however is that every calculator I've used (tried about 5 different ones from different sources) on the internet shows me at about half the calorie burn rate as the physical device. So say 100 per mile vs. 200 per mile.

So either the physical device is inflating my numbers even though they claim such a great algorithm, or the internet is missing key pieces of data due to no heart rate info (or possibly stride length).

It is not unheard of for stationary bikes or treadmills to under report calorie burn due to lack of heart rate monitoring so I'm wondering if this is similar.

Thankfully I am not dumb enough to use the extra calories I "supposedly" burn to eat more. So while I plan to stick to my current exercise routine and diet because its working, I am curious non-the-less over the accuracy issue.