Your Fitbit calorie adjustment is based on Fitbit's estimation of the total calories you'll burn over the course of the entire day at a given point in time. It's not "final" until approximately midnight, and varies throughout the day with your activity. For example (obvs all numbers totally made up):

MFP on its own, based on your stats and activity level setting, thinks you'll burn 2000 calories every day.

Have a great workout early in the morning. As of 9am Fitbit thinks you're going to have an extra-active day and projects you'll burn 2250 calories today and so at 9am your adjustment is 250 calories.

Then, over the rest of the day you're extra busy at work and barely move from your computer. As of 5pm Fitbit scales back that projection to 2100 calories for the day, so your adjustment changes to 100 calories.

And so on.

You can improve this by logging on to the Fitbit website (not sure if/how you can do this from the app), select "log" up at the top, under the food log section go down to "food plan" and see the little settings wheel in the upper right of the box? Click on it and, if you're currently set to "personalized," change it to "sedentary." That way, you'll have a really low adjustment in the morning (or even negative if you have that enabled) but generally it only goes up over the course of the day as you burn more calories, with maybe only slight backwards adjustments. That's the only thing I can think of that might help things; if that doesn't help hopefully someone else will have a better idea.

Good luck!

Mine did the same thing as milmil89 a few weeks back. I just broke the connection between the two programs and then reset it and it seemed to help.

I stand corrected; the adjustment is indeed based on MFP's estimate of your calories burned for the rest of the day, rather than Fitbit's. My apologies. I usually have a pretty good understanding of MFP/Fitbit stuff, having been a user of the two for about 4 years and pretty active with my own tweaks as well as in this group, but I learned something new today. Thank you for that, seriously.

I still wouldn't say that a swing in the adjustment of about 100 calories over the course of a day is "wild," though. I wouldn't jump to bug, personally. It still seems the result of normal fluctuations throughout the day, especially with morning workouts, and I think my comments about how activity over various points in the day impact your adjustment are still generally correct even if my original solution won't help and my original explanation of the system calculations were bad. To re-state my example above, using the same concepts but correcting the way the underlying math works:

MFP thinks that you burn 2000 calories in a day.

As of 9am, after a good morning burn, Fitbit says you've burned 890 calories so far. Using MFP's math, at 83.3333 calories/hour (2,000/24), you'd have an adjustment of 140 as of 9am (890 + [83.3333X15 hours remaining] = 2,140).

Then, you have a super busy day at work and don't do too much moving, so as of 5pm you've only burned a total of 1,457 calories. Using MFP's math, your total estimated burn would now be 2,040 (1,457 + [83.3333X7] = 2,040), so your adjustment drops to 40.

And so on.

I'll now revise my suggestions . First, syncing as often as possible can help smooth out any changes in your adjustment and being able to appropriately plan for them. Second, reducing your MFP activity level (such that MFP's estimate of your calorie burn is lower) can at least make it less likely that your adjustments will swing down so significantly over the course of the day if you normally have more activity in the morning (even though the adjustments themselves will seem bigger) - if, for example, changing your activity level from lightly active to sedentary means that MFP thinks you'll burn 1,800 calories per day rather than 2,000, that's now 75 calories per hour instead of 83.3333. If the day went exactly as above, your adjustment at 9am would be 215 calories (890 + [15X75] = 2,015) and your adjustment at 5pm would be 182 (1,457 + [7X75] = 1,982). The total adjustment still decreases, but by only 33 calories instead of 100. At the end of the day, though, no matter what activity level you choose, your eating goal would be the same as long as your selected deficit remains the same, so it won't change how much you're actually eating.

Now, if your fluctuations in your adjustment truly did happen over a matter of minutes, and it wasn't the result of syncing after not having done so in several hours, then I might investigate further, as noted above. Try to keep an eye on that exercise diary screen from the comment above, and if you're seeing crazy stuff, then you definitely might have an issue. However, your adjustment changing up or down over the course of the day as both systems adjust to your actual activity isn't unreasonable or unexpected on its own.

NancyN795 wrote: »

BarbieAS wrote: »

I still wouldn't say that a swing in the adjustment of about 100 calories over the course of a day is "wild," though.

Oh, I agree. You're completely right that a workout in the morning followed by a sedentary day will result in a bigger adjustment early and then a decrease in that adjustment later. And, you're right that choosing a lower activity level will make that change smaller. I was just reacting to this in the OP's question:

"One minute it's 139, then 62, then 40 something. How does it keep changing? I don't understand this.
I took a walk today for a half hour. At least. 139 seemed accurate. Ok... I just came back on to MFP and fitbit's estimate cut by more thwn half. Refreshed again and even more gone."

From that, I inferred that it was changing minute to minute, not over the course of the day. I keep getting hit by the bug that adds mysterious exercise calories into my MyFitnessPal calories burned number. Not every day, but probably once a week or so. It's frustrating even though I generally recognize when it happens and can compensate.

Agree fully. I was thinking of it more over the course of the day, but reading it more closely I totally see what you mean. Hopefully the OP will come back and clarify - I'd really like to help them get this right!

Yes, @Wickedfaery73 , that's how I do it. If I do any exercise that can't be properly tracked by my Charge HR (yoga, for instance), I manually log it in Fitbit, not MFP.

This issue is annoying me too! I have a flex and activity level set to active, with negative adjustments enabled. Thanks for the explanations.

This evening MFP had me as -69 calories for today based on my step count. I walked around the house a bit so my step count went up, but now it says -75.

It doesn't really matter in that the numbers are small, but I find it annoying that it changes around.