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.

[af7567]

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@shipo wrote:
Far from it, you need to take into account when beginning an exercise program your heart rate will initially increase to help you recover from the unexpected exertion; then, as your body gets into better condition, your heart rate will decrease

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Yes it does make sense that resting heart rate would increase if you had been doing more work than normal, but this would also increase during sleep too.

The problem I am seeing is that the fitbit is including reading from when I am not resting in the resting heart rate calculation. I am still "stuck" at 75. My sleeping heart rate is always between 58-70. Every day when I wake up fitbit will say my resting heart rate is 74, sometimes 73. But then during the day it will randomly go back up to 75 even though I haven't done any resting at all.

So there must be an error in the way the fitbit is detecting daytime resting.

[Oregonmama]

Agreed. It might make sense when going up, but makes no sense at all when
going down. My job involved a lot of walking. The first weeks of the
pandemic, my step count dropped by about 10k steps per day. I went from ❤️
hours sedentary a day to >10 overnight. In spite of the radically increased
stress levels, my FitBit said the RHR went down. Given the numbers I was
looking at, I had always suspected my FitBit was including hours I was
walking in my RHR calculation. Once this happened, it was quite obvious.
Knowing more than a little about math, I have a pretty good idea how/why
this is messed up. They need to have some way to handle those who aren't
sedentary nearly as much as they predict, and it wouldn't be hard, However,
they instead choose to tell us there's nothing behind the curtain. When I
first bought my FitBit, I was thinking I would buy one for others in the
family, but issues like this one (and who bought them) means I won't be
buying another.

[af7567]

Over the last couple of weeks I have been doing a little experiment, and I have got my Fitbit RHR to go from 77 to 71. My heart rate when waking up and relaxed is 68-70 so 71 is close enough to what I think my real value should be.

I got it to go down by trying every day to really spend some time relaxing, by sitting on the sofa and reading. This should give fitbit some daytime rest time to use in its calculations. I very rarely sit on the sofa normally.

The other thing I did was turn off heart rate readings on the fitbit when I was active but not walking, such as when working at a desk or standing around doing stuff in the kitchen. This made sure my active heart rate wasn't being counted as resting.

[RobertRB]

If this is the method for calculating my RHR then my Sense is not working properly. I watched my HR last night for 45 minutes as I sat watching TV. I did not move out of my chair. My HR never got above 61 yet this morning(I wear it to bed) it reported 64. My lowest for the day was 56. Is my Sense faulty?

[Lindachocolate]

My question : when it says my RHR is 66, but when I look at the graph, I see the 'lowest' resting was 55 (I exercise a lot/ no heart issues here):

Does Fitbit take the 55 resting heart rate into account & average it in when it gives me a RHR.          (resting heart rate) of 66 ?

I realize everyone's nos are different, but above is my case.

[Lindachocolate]

Quick question- do u wear ur watch to sleep ? Not sure if u said u did, but if not, that might explain it.

[kgabelsb]

I just read through a lot of these messages because I am having the same problem with the resting heart rate calculation algorithm.  It seems to me that Fitbit would take all these (and many other messages) into consideration and update their algorithm to give a true resting heart rate that is based on actual current readings and not an average over X number of days.  Do we think this will ever happen?  Haven't enough of us complained that the developers would take note?  I do not see that Fitbit is very proactive in listening to its users.  Maybe we all need to move to an an Apple watch ...

Although I love my Fitbit Charge 5, I would like to see that it be more accurate on not only the resting heart rate but other things that it is supposed to be measuring ...

[Money4dogs]

So to be specific, would it be accurate to say the resting heart rate (which is calculated first thing when you wake up) is a combination of:

1) sleeping heart rate the night before, and

2) heart rate throughout the prior day while you are awake but inactive (no steps detected)

Then Fitbit's algorithm calculates the 2 above factors and spits out a Resting Heart Rate the morning after?

To use a specific example, a Resting Heart Rate on Wednesday morning consists of Tuesday night sleeping heart rate combined with Tuesday day time inactive heart rate? 

[AquamanJon]

I don’t think we know. It’s proprietary. Some mathematical amalgam of your entire days HR minus something.

However. There is a small dose of adrenaline that raises your HR at wake up. If it were measured then. That might account for the skew.

Jon Wallace
301-639-2787

[crb83]

I have a serious gripe with the way FitBit calculates the resting heartrate. It uses the "average sleeping heartrate" as a factor. But it should really be the lowest sleeping heartrate. Here's an example: My HR dips to 42, 44 etc in my deepest sleep, but i have restlessness in other periods of the night so my "Average HR" during sleep ends up being 54, 55 etc.  Now in the morning fitbit uses that number and makes my Resting HR officially around 65 for the day.  Meanwhile later on im motionless watching tv and my fitbit reads my HR in the low 50s.

Clearly my actual resting HR is abt 10 beats lower but because of how fitbit calculates, it doesnt reflect. I cant be the only one noticing this, and this seems to he a busy topic on here. Will fitbit ever update the way it calculates Resting HR?

[kgabelsb]

I don't know ANYONE that is happy with the fitbit algorithm for calculating resting heart rate.  Maybe if enough of us keep complaining, they will someday change it to be more accurate.  I considered getting an Apple watch but the reviews indicate that their sleep reporting isn't as good as Fitbit's.  I wish there was some way that Fitbit could be more responsive to its customers.  I was hoping that with the Google takeover, that things would get better and I have to admit I have seen some positive changes.  It used to be impossible to contact anyone at Fitbit, and now when I have an issue, I am able to do a chat. 

[Rcnelson56]

I know this is an old discussion but it is one that I’ve never felt was adequately answered. My take on the resting heart rate is that it will never show huge variations from one day to the next. That said, for most of December 2022, my RHR was in the low 70’s while the year average was 67 as it has been for the past few years. Last night from the time I went to sleep til I woke my HR never  reported above 67 and mostly remained in the low 60’s. Why wouldn’t my RHR be a more accurate reflection of that nights HR? 

[Metsci]

This thread is now 7 years old.

Fitbit is not going to help us.

Let's let the thread die a peaceful death.

[CharlieTets]

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

My guess how this works by looking at my data is as follows:

It takes last 2 weeks low HR during sleep and weighs most recent sleeps a little heavier . Than adds about 20% to that in addition it will check you HR when your inactive. It will weigh these 2 results with heavier weighting on sleep HR. 

A couple reasons I think it works a little like this or a variation of this. 

1) Whenever I have a bad sleep or eat before going to bed my low sleep HR will be drastically higher than usual and it will move my resting HR up but only a portion of the delta between my normal low sleep hr and higher sleep hr. 2) let's say I eat badly for a few days the resting HR will go up a non-trivial amount. Then it will take about 2 weeks to get back to normal:  If I do the opposite and am very healthy and have a low sleeping HR it will only drop a little bit it takes about two weeks to drop the HR back to the normal rate 3) After doing extremely intense excercise resting HR will increase a bit but likely because of a combination that you are recovering and your low daily inactive heart rate is higher as well as your overnight low sleep HR. It intuitively feels like the resting HR is pre-dominantly determined by the low HR during sleep as it almost always changes in the direction that I expect after I sleeping.