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.

[Kagakusha]

You should not be at all concerned at a resting heart rate in the 50’s if you are fit.
Overnight, sleeping figures in the upper 40s
are not at all uncommon.
However, these are for fit people; numbers that low if you don’t exercise etc might merit mentioning to your doctor.

From my iPhone - please excuse spelling checker induced nonsense!

Moderator edit: personal info removed

[TinaMarie73]

Thanks for the information.I truly hope everything ok. It’s like when I’m sitting you can see heart rate drop down in the upper 40s and low 50. Then it gets in Mid 40s at night. I was told Fitbit is off by several beats but I’m not sure. Where everything is going on with the Coronavirus kinda scared about going to doctors right now. Anxiety and stress could be making it drop too. I really don’t know.

[Du92979]

I workout dally.
--
Sent from my iPhone

[TinaMarie73]

I walk on most days at least 2 miles and for the whole day I usually get 4 to 5 miles with everything I do.

[wissajane]

It seems very apparent that fitbit wants us to turn on the tracker.  I refuse to do this!   It's obvious who the automatic responders are.    So, is the final word that resting heart rate is the average of resting times during the day (which could vary greatly) and resting heart rate at night?  

[TwiiK]

I just got a Fitbit Charge 4 last week as my first ever fitness tracker / smart watch and so far I'm not very impressed. Keeping in line with this topic it consistently measures my resting heart rate as being way higher than it actually is.

My resting heart rate is in the low 40's. Measuring with a stop watch, my own fingers on my own pulse in the morning after I wake up consistently give me these numbers. Even the Fitbit itself shows me this as my current heart rate, but still it shows my resting heart rate as being around the 50 mark, which is almost 25% higher than it actually is.

"MariamV: This is calculated by Fitbit algorithms (it's like the secret recipe)"

Well those algorithms are useless.

This means the Fitbit resting heart rate is possibly only good for comparing against itself, but so far other areas of the Fitbit app have shown me not even that holds true. There is for example no correlation between the sleep analysis or sleep score and the actual feeling of being rested meaning the entire sleep tracking is useless as well. I've had the same sleep score every day since I got the device yet on certain days I've barely slept at all, for example due to being drunk/hungover, yet Fitbit is not able to detect this in the slightest.

[smnickel]

This is still confusing to me. My resting heart rate is always in the mid to high seventies.  However most mornings when I wake up and check my HR overnight the average rate is usually in the high 80's.  If fitbit calculates RHR while at rest and sleeping and my average rate is 89.....how can my RHR be 75?

[Yotko]

I'm not entirely thrilled by this answer. When I look at my rhr of 52 and I see long periods of sleep in the low 40s, and I combine that with low 50s measurements during the day, I gotta think that whatever "secret algorithm" you're using has some bad weightings in it. 

[Kellie_1993]

I wear my Fitbit to bed and all day. My resting heart rate was 55bpm and somehow it's gone up to 62bpm! Which has also effect my fitness from being good/very good to only good. I have been doing more exercise than I ever have, I'm fitter than I ever was yet it's rising. When i look at my Fitbit when I am not doing anything etc it's 55bpm so why is it recording much higher? When I wake up I tend to get straight out of bed, should I be waiting for a minute or so as it's so inaccurate.

Sorry, also if I look at my heart rate through the night it's been as low as 50bpm? So if it's calculated as you have said enough surely my resting heart rate should be much lower. Bit disappointed to be honest. 

Moderator edit: merged reply

[Manupuri42]

I feel it is generally a little above average sleeping heart rate. So if you are subscribed to their premium service you can have access to detailed sleeping heart rate graph and average sleeping heart rate. And obviously the RHR fluctuations are slow as compared to day to day heart rate fluctuations.

[Oregonmama]

See if your heart rate is higher when asleep. If so, that's the issue. If
not, ignore your Fitbit RHR. It doesn't really have anything to do with
whether you are resting or not. It's just some form of computation over all
(or maybe all except when the Fitbit calls you "active") your heart rate
measurements over the day and night. If you are walking a lot or doing a
lot of housework, it will read high.

[Kellie_1993]

My heart rate when I sleep goes as low as 50bpm so it's even lower again. It's just pants as I was working with it to find out that it's not accurate really. I have also found when I do my interval training the calories burnt is not accurate as well. I'm slowly realising Fitbit might not actually be very good for accuracy.

[Gladieva]

I wear my fitbit to sleep and it does the same thing.

My resting heart rate shows as 65 but during the night it goes all the way down to 54. 

It seems to me like the fitbit app calculates the average resting heart which is different. 

[Manupuri42]

Well my RHR hovers from 60- 67. While sleeping my heart rate generally touches 50 and sometime below 50 aswell but my Average Sleeping Heart rate(ASHR) averages around 56 - 62. Its the ASHR figure which you get in fitbit premium that is important. If I have had alcohol before sleep my average sleeping heartrate goes up to anywhere 64 - 70 which generally bumps my RHR by a couple of points for the day due to higher ASHR. So with my normal ASHR of 56 - 62 I have RHR of 60 - 64 depending on quality and amount of sleep. So its pretty close to ASHR. Therefore I feel that RHR is more or less determined by ASHR.

[Metsci]

Isn't it time to give this whole RHR thread a rest unless some can get
Fitbit to tell us what their algorithm is?

[Babinator]

Nope.

Sent from my iPhone

[AquamanJon]

Back in the dark days of HR training. You woke up. Allowed your heart rate to settle. Waking up includes a little dose of Adrenalin that pushes your rate up a little. You took your rate and that was your rate! Far more accurate and dependable. The idea that their is an algorithm to compute your RHR is by itself maddening. It is a re-defining of HR and RHR. An artificial altering of the definition away from a medical definition. And the more extraneous factors it includes, the less dependable it is! Twice now, based on fitbit data, I have gone to the doctor with concerns about my heart. And twice with EKG he hasn’t told me there is nothing wrong with my heart. Fitbit computation of RHR is a farce. Aside from trends. Ignore it.

So i just reviewed a whole bunch of my own graphs, Because your RHR is computed by an algorithm rather than just checking and recording it, the way to lower your fitbit RHR is to discontinue your exercising and thus eliminate both the Workout spike and then the subsequent recovery period. 

Moderator edit: merged reply

[Yotko]

Yeah I think you're right. I've been tracking it myself for a couple of weeks now and the Fitbit RHR is between 10 to 15 BPM higher than my actual manually tracked RHR.  This morning's report was 55 and my actual RHR was 42 when I measured it manually upon waking. 

The thing that really sucks is that it also affects your cardio fitness rating as well. 

I guess I'll keep using it to track trends but it's very disappointing that these stats are so incredibly inaccurate. 

[AquamanJon]

We all want to see a grade. Improvement. Human physiology is so different from testing subject to testing subject. When I was doing Ironman, my RHR was low 60’s. Which would be high for most people in a similar training regimen. That is also probably the thing that’s kept me from going fast fast in racing. In diving physiology, there is no predicting how someone will react physiologically to either breathing gas or pressure. A seemingly non dangerous situation can’t result in decompression sickness and no one knows why. Do I trust Fitbit’s fitness rating? Not at all because it cannot measure individual physiology. 

If you want a true indication of fitness improvement. Graph average heart rate over speed on the same course, over a period of time. Fitbit WILL give you a fairly accurate measurement of average heart rate. 

[BretAllen]

I have been using a fitbit since 2015 almost 24/7, it seems to me that its not really showing resting heart rate but a daily average heart rate.  Correct me if YOU THINK I'm wrong.  🐵