Fitbit resting heart rate

I wrote an earlier post reviewing the Fitbit charge 4.  Overall it is a good piece of equipment.  One of the main issues I noticed was the resting heart rate seemed odd.  

Since then I have kept an eye on it, and the resting hears rate algorithm is clearly not accurate!  Some days my heart rate is constantly above the 'resting heart rate'.  Even when I am asleep.  

The screen shot below is a perfect example.  I did not do any aerobic exercise and was sitting around almost the entire day.  My heart rate never dropped below 84, yet my FitBit Charge 4 calculated my resting heart rate as being 79.  The following day it estimated my resting heart rate to be 77, so it doesn't appear to be averaging over a longer timeframe.  

Never dipped below 84

There are plenty of days like this where my fitbit estimates a resting heart rate that is not right.  

The screenshot below it estimated my resting heart rate to be 77.  On this day my heart rate only went as low as 77 twice in that day, and was significantly above this for the remainder of the day and night.  

If you think the fitbit's algorithm excludes any exercise when calculating resting heart rate, that still wouldn't explain what you see here.  I did not do any aerobic exercise and was sitting for most of that day.  I was working from home that day, so didn't walk to or from my car, I sat in front of a computer all day, and rested in the sun on my deck at lunch time.  I would not have travelled more than 30 meters from my bed that day.  

Only down to 77 twice

Below is another example.  On this graph my heart rate dipped to 80, only twice, and only briefly.  Once around 2am the other around 4am, I was possibly asleep during those times.  Other than that my heart rate was above 80.  Somehow it calculated my resting heart rate to be 80.

This time I worked from the office, so walked to and from my car.  I spent the rest of the day sitting at my desk.  I may have gotten up once or twice to walk to the kitchen or go to the toilet, but there was no exercise.  I didn't even go for a walk at lunch that day.  

Resting heart rate of 80 - but how?

The FitBit Charge 4 is not accurate when estimating resting heart rate.  If you are thinking of getting one, it tells the time well, it seems to count heart beats accurately, but the algorithm that estimates resting heart rate is massively inaccurate.