How does Fitbit calculate Resting Heart Rate?

[BigHaole]

I'm finding this very frustrating to be sitting at my desk, and see my HR showing as 74, but my Resting HR being 80.  Clearly Fitbit is not using the conventional definition (from Wikipedia):

"The basal or resting heart rate (HRrest) is defined as the heart rate when a person is awake, in a neutrally temperate environment, and has not undergone any recent exertion or stimulation, such as stress or surprise."

This definition would lead me to expect my reported resting heart rate to be the low value reached in the early morning, or at least the low value I reach, during the day.  Instead, it's above both of these.  I would like to know how it is being calculated, so I can know if my Fitbit is reporting anything useful when this number goes up or down.  Over the recent new years holiday, I got more sleep and more exercise, with less stress, so I was expecting this to go down, but it has gone up and I do not understand why.

[arkaycee]

@cctennant, since "Moderator Edit: removed link" happened, we can't see your instructions. I'm guessing there's some "no external links" policy on the Board. Could you just post the instructions in this thread?

[StephB17]

Yes, they did not like the reality of my post which is the inaccuracy of their heart rate monitor.

Against my personal preference I am switching to the apple watch.

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[cctennant]

@arkaycee The policy isn't against external links AFAIK, but against commercial promotion.  From the policies, "Please refrain from posting content that would constitute advertising, spam, or any other form of unauthorized solicitation."

However, the source code that I'm offering isn't for sale -- it's free code that I'm hoping will help others get more out of their FitBit device.  I responded as such to the moderator who removed my link, but didn't get a response.

So I'll try again   The link is: https://fitbit.myheartstats.com.  And to make this really clear, I'm not selling anything.  I'm offering working code in the spirit of the first sentence of the community guidelines:

"The Fitbit Community is a community of real people who exchange ideas, solutions, tips, techniques, and information about the Fitbit products and services they love."

One note about the app -- it works on mobile browsers, but it doesn't work well if you save it as a mobile app (you have to re-authenticate each time).  I've been meaning to fix this, and if enough people ask me, I certainly will 

@StephB17 I don't think the issue is the accuracy of the heart rate monitor per se.  The monitor itself is quite accurate enough to produce good data for resting heart rate.  The problem is that FitBit's "secret sauce" resting heart rate algorithm, which crunches that raw data, is frustratingly inconsistent.  Fortunately, FitBit makes that raw data available through their APIs, so you can try the code in the link to see if this calculation works better for you.

[FerdinandFitbit]

Thanks a lot for clarifying that @cctennant. I'll leave the link here this time.

Thanks for contributing!

[SunsetRunner]

Why does Fitbit delete posts that are harmlessly criticizing their calculation of RHR? I wrote a big post comparing it to AW4 and saying RHR is ALWAYS at least 5 beats off the lowest HR, in sleep and resting state. And they deleted it. Fantastic job Fitbit! 

Today I got 47 lowest heart rate awake and less than 50 in sleep and Fitbit says 54 RHR while AW4 says 49/50! Nice! 

[Vezza79]

It seems that the biggest factor in the resting heart rate that I’m given is the lowest recorded heart rate overnight, even if it only goes that low for a few minutes and is actually more raised for the rest of the night. Can you please explain if my observation is correct? Thanks

[Kagakusha]

Your observation agrees with my experience. If for whatever reason you have a restless night, the unpublished Fitbit algorithm raises the reported ‘resting heart rate’.

However Fitbit’s definition of ‘resting heart rate’ does *not* agree with any other definition of resting heart rate (which is rather poorly defined) that I can find. It can only legitimately be compared to other Fitbit measurements - for example a trend over a long period. Any comparison to values measured in other ways is meaningless.

Moderator edit: personal info removed

[Ravinmc]

It is interesting and perhaps unfortunate that Fitbit has determined  the most significant and important metric to calculate from our heart rate data. Knowing the high the low and the mean of our waking and sleeping hours would be of most value.

[RachelH93]

This isn’t true. My lowest heart rate in 24 hours is consistently 48 but Fitbit says 57. It’s conpletely off. 

[Vezza79]

Hi Rachel, I’m not saying that my lowest heart rate is given as the average resting heart rate. I too have a similar gap between what it shows as my lowest and my resting. My point is that my overall resting heart rate appears to be unduly influenced by the lowest heart rate overnight, even if that lowest point is only for a few minutes.

[Vishalk]

I would disagree with your explaination about wearing it at sleep. I do think consistently Firbit is showing resting HR as at least 7-10 bits than actually it is. My guess is that it takes into account min HR while asleep and prev day RHR  I have not seen RHR varying more than 2 bits on any 2 consecutive days.

If I export same data to google Fit it shows it bit closer to reality.

[ZumbaSteph]

I wear my Fitbit charge 24/7 and frequently my HR when I first wake up is 38 to 43 bpm, which is normal for me. I am an endurance athlete, and, although my cardiologist is a bit concerned at me being bradycardic, again, this is my baseline. But my Fitbit charge app only reads to 45 bpm. Period. It never shows below 45 on the RHR chart. Ever.

[Tracybrit]

That’s very confusing.  Why is my heart rate higher when I am asleep than during my non active periods during the day?

[Kagakusha]

I have very occasionally seen that pattern too.
Having dug around in the scientific literature on this subject quite a bit, I think the honest answer is that nobody has any idea!

[TinaMarie73]

I don’t understand it either I know they say at night it can drop as low as the 40s during sleep and it can be normal, My RHR has got down to 50 while sitting and I do  walk most days. But my average rate for Fitbit for a day is 57 and don’t understand how they get that number. It’s kinda scary when you feel it’s not in normal range.

[jpsfla]

I was wondering if something changed when the sync problem to my fitness pal occurred.  I don’t remember the date that happened but on May 19th my resting heart rate dropped 9 points and now has gone down another 4 points.  This may be a correct measurement and I have to go in for a Holter monitor next week.  If this is right it may be a good tracking device!!

[TinaMarie73]

I’m not really sure how long you been exercising but that does seem like a lot of points to go down . Unless you didn’t have a high resting heart rate to start with and are in good shape. I’ve never really known for sure what my resting heart rate was. I got this device to start trying to get more steps in. I do walk a lot but that’s all I do. So normal is supposed to be 60 to 100 that’s what made me so scared. Mine gets down to 50 sitting sometimes and I know I’m not athletic. But I hope everything will be okay when you wear heart monitor and you can put mind to rest. I really don’t know much just what others have shared. 

[jpsfla]

Thanks for replying, I’m 78 and have been pretty active all my life but my resting rate has been 58 to 63 for many years. The problem appears to be an intermittent heart beat or something because my Fitbit will not show stages of sleep now, saying it can’t get enough of a regular beat. I have had skipped beats for years and EKGs have been ok until now. That missing sleep stages is the only thing the Fitbit shows different except for the resting rate of 46.

Sent from my iPad

[TinaMarie73]

Well I hope they can figure it out for you. I know it’s scary to think something is wrong. But maybe it’s just not reading the beats and nothing is wrong. I sure hope it all turns out well. Keep me posted. I worry about mine too.

[gateswood]

I imagine this post will be censored rather quickly but you should know the fitbit records a heart rate reading every 5 seconds. If you want to see the raw data, you can sign up at squash leagues dot org and download your actual recorded heart rates without any cooking by algorithm. You can view this data in a variety of ways and some of the ways will result in very large files to download.