Fitbit and MyFitnessPal

mattprice240
mattprice240 Posts: 3 Member
edited November 29 in Health and Weight Loss
Yesterday I bought a Fitbit and have been testing it out today.

I’m a little bit confused about calories burnt through exercise after I linked up the Fitbit to MFP. The calories burnt through exercise seem much than when I was just using the app? Today MFP (after being synced with the Fitbit), is saying I have burnt over 1300 calories whereas yesterday I did the same workout and same exercise and it said under 900 calories burnt.

How does Fitbit calculate the total calories burnt and how does that sync with MFP?

Thanks in advance for anyone who can clarify this for me!

Replies

  • shadow2soul
    shadow2soul Posts: 7,692 Member
    The adjustment on MFP is:

    Fitbit TDEE* - MFP estimated burn = +/- adjustment

    *This number is estimated based on what Fitbit said at your last sync and your activity level setting on MFP. If you have MFP set to anything above Sedentary, your adjustment could decrease before the day is over since periods of inactivity will be a lower calorie burn than MFP’s estimation.
  • shadow2soul
    shadow2soul Posts: 7,692 Member
    Here is an example of how the math works:
    Lightly Active MFP estimated burn (based on my stats): 1914

    That breaks down to:
    79.75 calories per hour
    Or
    1.329 calories per minute

    Now as of 12:30 pm my Fitbit calorie burn is 910.

    So there is 11 hrs 30 mins MFP has to estimate calories for.

    11 * 79.75 = 877.25
    30 * 1.329 = 39.87

    910 (Fitbit) + 917.12 (MFP Lightly active estimation for remainder of day) =1827.12

    So MFP is estimating that based on my current Fitbit burn and my lightly active setting on MFP that Fitbit say I burned 1827 by midnight. It uses this estimation to form an adjustment.

    1827* - 1914 = -86

    So currently I’m losing 86 calories. However after each Fitbit Sync, MFP will redo it’s math estimation for the day. It could increase or even decrease. MFP won’t stop this estimation calculation until around midnight when the Final calories burned # is sent over to MFP from Fitbit.

    The higher your activity level setting is on MFP the higher it will estimate your remaining calorie burn and the more likely you will see a huge adjustment early in the day that decreases later. On the opposite side if you are set to Sedentary, but are actually really active you will see a large adjustment by the end of the day.
  • babysaffy
    babysaffy Posts: 232 Member
    Thanks for this post and the responses. Very useful! I got my fitbit last month and was struggling with the erratic adjustments throughout the day so yesterday I changed my activity from active to lightly active.

    Psychologically, I'd rather start the day with a lower calorie allowance and earn more from my activity as the day goes on than start the day with a negative adjustment and one hour seeing hundreds of extra calories then the next seeing I'm actually in the red as has been happening for the past month since I allowed fitbit to make negative adjustments to my daily allowance.

    Today has been much easier. I'd suggest looking carefully at the activity level you've set.
  • ghudson92
    ghudson92 Posts: 2,061 Member
    If you have a fitbit, don't log your exercise through the mfp app as this will confuse things and inflate your calorie burn. The fitbit will adjust to you over time.
  • mazdauk
    mazdauk Posts: 1,380 Member
    Fitbits can over-estimate calorie burn by up to 40% according to Which? reports, so keep an eye on it. That's why I don't sync my tracker to MFP, just add it separately
  • WinoGelato
    WinoGelato Posts: 13,454 Member
    It can take time for FitBjt and MFP to get truly in sync with your patterns of activity, calorie burn, etc. make sure all the settings are consistent and that you have negative adjustments enabled and then give it a couple of weeks before you start making adjustments or thinking it’s not right.
    The two work off of different algorithms so comparing what you see in one system vs the other will likely not match up but I’ve used a FitBit synced with MFP for 5 years now and found it to be very accurate. I lost the weight I set out to lose and am currently maintaining while trusting and eating back those adjustments.
  • Rayvis1014
    Rayvis1014 Posts: 36 Member
    Just so you know, I once put my fitbit data and calories in a spreadsheet over six weeks, and it perfectly calculated my TDEE every day. My actual weight lost vs. expected weight lost (calories in vs. calories out) was off by only .2 lbs over six weeks. I now I trust my fitbit's calculation of my TDEE. I think some people who believe it overestimates might not realize that it adds calories burned to your BMR, so it's getting a running total for the whole day. I don't pay attention to the number until the end of the day, when it shows me my TDEE. I also avoid eating at different amounts each day by using the average instead of the daily total to calculate my deficit.
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