Accuracy of Fitbit calories burned

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  • Maxematics
    Maxematics Posts: 2,287 Member
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    I find that my Charge HR is accurate. I think for some people, not all, they find it inaccurate not because the calories are too high, but because they think they're eating the calories Fitbit says they can, but they're not. Without a food scale it's all just even more estimations on top of the Fitbit calorie estimation. So if they're trying to take advantage of every last calorie, they may actually be going over by several hundred.

    Anyway, I think people can underestimate their level of activity too. 20K steps and up will never be lightly active. 10K is already lightly active. Most people, especially in the US, get no more than 5000 to 8000 steps per day. THAT is what sedentary is.
  • PAV8888
    PAV8888 Posts: 13,930 Member
    edited February 2016
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    synacious wrote: »
    I find that my Charge HR is accurate. I think for some people, not all, they find it inaccurate not because the calories are too high, but because they think they're eating the calories Fitbit says they can, but they're not. Without a food scale it's all just even more estimations on top of the Fitbit calorie estimation. So if they're trying to take advantage of every last calorie, they may actually be going over by several hundred.

    Anyway, I think people can underestimate their level of activity too. 20K steps and up will never be lightly active. 10K is already lightly active. Most people, especially in the US, get no more than 5000 to 8000 steps per day. THAT is what sedentary is.

    Based on currently available evidence, we propose the following preliminary indices be used to classify pedometer-determined physical activity in healthy adults:
    (i). <5000 steps/day may be used as a 'sedentary lifestyle index';
    (ii). 5000-7499 steps/day is typical of daily activity excluding sports/exercise and might be considered 'low active'; (iii). 7500-9999 likely includes some volitional activities (and/or elevated occupational activity demands) and might be considered 'somewhat active'; and
    (iv). >or=10000 steps/day indicates the point that should be used to classify individuals as 'active'.
    Individuals who take >12500 steps/day are likely to be classified as 'highly active'.
    http://www.ncbi.nlm.nih.gov/pubmed/14715035

    My own observation of the correspondence between MFP and Fitbit is:
    MFP Sedentary: 3500 to 5000 steps
    MFP Lightly Active: 5000 to 8000 steps
    MFP Active: 8000 to 12500 steps
    MFP Very Active: 12500 to 15500 steps
    Exceeds MFP Very Active: above 15500 steps
  • ForecasterJason
    ForecasterJason Posts: 2,577 Member
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    Here's the thing. Yesterday I walked outside for about 30 minutes, which includes going up and down hills. Based on my distance, I was walking about 3.2 mph. According to my Fitbit I burned about 200 calories in that time for walking about 1.5 miles. According to the formula that the device uses for BMR, my BMR is in the 1500 range. Based on the MET's that I would have had from my walk, I don't see how that can be correct.
  • GetThatRunnersHigh
    GetThatRunnersHigh Posts: 112 Member
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    My own experience with Charge is that it's fairly accurate. It gives me ~500 calories for an 7 mile run. I've been eating all the FitBit calories and I've been maintaining for a year now.
  • Mouse_Potato
    Mouse_Potato Posts: 1,503 Member
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    I have a Charge HR and I finds it underestimates by ~100 calories a day for me. I think it is because a lot of my activities are not step-based (see profile picture) and it doesn't really know what to make of them. An hour of aerial silks usually nets me about half what I would get for an hour of walking at a normal pace. And Pilates counts the same as reading on the couch while sipping wine. :smiley:
  • Bbeliever215
    Bbeliever215 Posts: 234 Member
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    I walk an average of 25k steps daily ( I typically do high stepper challenges ) and I have been nervous about eating my fitbit calories because they're so high, however I est most of them, if not all at times and have been losing. Slowly but losing. On my rest days, which I tend to average about 12K steps I burn around 2500 or more. I have only had my charger hr since Christmas but I think it's fairly accurate. I am also into strength training and I am not sure how that influences things.
  • Christine_72
    Christine_72 Posts: 16,049 Member
    edited February 2016
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    scolaris wrote: »
    Today my Fitbit HR told me I burned 2864. I walked over 19k steps and lifted weights for 30+ minutes. I hoped telling it I'm 1" shorter than I really am would help but now in worried...

    @scolaris I reduced my height and stride length by 1 inch too. I can't tell that it made any difference. Have you noticed any difference with your numbers?

  • williams969
    williams969 Posts: 2,528 Member
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    When I had the Zip, it tended to UNDERestimate. For reference, all my cardio was step based (light jogging/walking), and I ligged strength training through manual entry. I told it I was 5 inches taller (but kept stride length true to resl life) to make it accurate for my personal experience.

    Then I traded up to the Charge HR. In the year I've had it, I've found it much closer to accurate. I've only made a 1inch adjustment. Seems spot on, more or less.
  • PAV8888
    PAV8888 Posts: 13,930 Member
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    Fitbit seeks to encourage people to move more.

    The basic Fitbit formula ought to under-estimate most people for whom Mifflin St Jeor holds true. Fitbit assigns straight BMR to any time period it doesn't detect movement. If you look into the MET tables, this is an under-estimate as many non movement generating daily living activities would get you MET 1.3ish. In fact, if you factor in corrected METs this could be even more for many people.

    So yes, Fitbit gives you perhaps a little bit more than straight MET value for your walking; but, it tends to average out JUST FINE because most people have way more periods of low activity than periods of high activity during their day

    In any case, there is a heck of a lot of difference between I need to run a 1%, 5% , or even 10% correction to my Fitbit TDEE estimate, and OMG I can't trust the calories my Fitbit gives me, I don't eat any of them back (or even I eat 50% of them back given that a Fitbit TDEE adjustment is not a true exercise adjustment and should not be eaten back at only 50%.)

    For most people we are discussing a sub 10% correction which would be smaller than the total deficit/surplus they are running. And if you connect Trendweight to Fitbit, reviewing how far off your logging is from your expected results is relatively easy!

    Of course, as already mentioned, the quality of your food logging also matters: if you are 20% too low when it comes to recording your food intake... yes, Fitbit will "overestimate you".

    Like many things in life: trust AND verify!
  • ForecasterJason
    ForecasterJason Posts: 2,577 Member
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    PAV8888 wrote: »
    Fitbit seeks to encourage people to move more.

    The basic Fitbit formula ought to under-estimate most people for whom Mifflin St Jeor holds true. Fitbit assigns straight BMR to any time period it doesn't detect movement. If you look into the MET tables, this is an under-estimate as many non movement generating daily living activities would get you MET 1.3ish. In fact, if you factor in corrected METs this could be even more for many people.

    So yes, Fitbit gives you perhaps a little bit more than straight MET value for your walking; but, it tends to average out JUST FINE because most people have way more periods of low activity than periods of high activity during their day

    In any case, there is a heck of a lot of difference between I need to run a 1%, 5% , or even 10% correction to my Fitbit TDEE estimate, and OMG I can't trust the calories my Fitbit gives me, I don't eat any of them back (or even I eat 50% of them back given that a Fitbit TDEE adjustment is not a true exercise adjustment and should not be eaten back at only 50%.)

    For most people we are discussing a sub 10% correction which would be smaller than the total deficit/surplus they are running. And if you connect Trendweight to Fitbit, reviewing how far off your logging is from your expected results is relatively easy!

    Of course, as already mentioned, the quality of your food logging also matters: if you are 20% too low when it comes to recording your food intake... yes, Fitbit will "overestimate you".

    Like many things in life: trust AND verify!
    Yes, this is true. For me, I think the difference is up to about 8-9% a day, and a lot of days I happen to fall a bit short of what it says anyway without really making an effort.

  • scolaris
    scolaris Posts: 2,145 Member
    edited February 2016
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    This has been really helpful!
    @PAV8888 thank you for all that analysis
    @Christine_72 too soon to tell, but I think it's believable. I'm really trying to streamline things. If I burn 1200 calories by noon according to the HR, I know I'll burn 2400 or better by midnight and then I can just relax and plan to eat 1800-2000 calories. Simple! But I don't want deficits that are too big, either, so then whenever I go over 2500 I have to decide if I'm going to eat a little more. Ugh... decisions... Still working it out.
  • PAV8888
    PAV8888 Posts: 13,930 Member
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    People who enable negative adjustments are sometimes confused by the calories they "lose" by going to bed early, or by watching TV before midnight.

    This is an artefact of the way MFP calculates the Fitbit adjustment.

    The MAXIMUM number of calories you MIGHT lose to midnight can be predicted as follows:
    MAX_CAL_LOST = BMR / 1440 * M * F

    where:
    BMR = BMR as calculated here: http://www.myfitnesspal.com/tools/bmr-calculator
    M = Number of minutes you will be less active than your MFP activity setting between time of sync and midnight.
    F = factor calculated as:
    0.25 if you are setup as Sedentary in MFP
    0.4 if you are setup as Lightly Active in MFP
    0.6 if you are setup as Active in MFP
    0.8 if you are setup as Very Active in MFP
  • scolaris
    scolaris Posts: 2,145 Member
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    Thanks!
  • Sonyavdg
    Sonyavdg Posts: 17 Member
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    I have the charge (not HR) and it seems to be very accurate. As of this morning, my deficit as calculated by trendweight (based on actual weight lost) and my 30 day average deficit based on Fitbit calories burned and MFP logging for calories eaten are within 20 calories a day of each other.
  • Maxematics
    Maxematics Posts: 2,287 Member
    edited February 2016
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    PAV8888 wrote: »
    People who enable negative adjustments are sometimes confused by the calories they "lose" by going to bed early, or by watching TV before midnight.

    This is an artefact of the way MFP calculates the Fitbit adjustment.

    The MAXIMUM number of calories you MIGHT lose to midnight can be predicted as follows:
    MAX_CAL_LOST = BMR / 1440 * M * F

    where:
    BMR = BMR as calculated here: http://www.myfitnesspal.com/tools/bmr-calculator
    M = Number of minutes you will be less active than your MFP activity setting between time of sync and midnight.
    F = factor calculated as:
    0.25 if you are setup as Sedentary in MFP
    0.4 if you are setup as Lightly Active in MFP
    0.6 if you are setup as Active in MFP
    0.8 if you are setup as Very Active in MFP

    I have negative adjustments enabled and don't lose any calories except for the morning. The best way to utilize Fitbit/MFP, in my opinion, is by changing your food plan from personalized to sedentary and keeping yourself sedentary on MFP as well. With sedentary you start low and earn calories throughout the day, but with personalized Fitbit tries to predict what you'll burn before you actually do. That constant calorie shift can be frustrating for people.

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