1 place for potential problem - especially starting out.

Fitbit setting - Calorie Estimation is enabled by default in your profile.

This starts the day with an assumed daily burn based on historical records, and until a device sync provides data to show otherwise, that's the burn data given to MFP to do it's math with.

So if Fitbit thought you'd burn 2400 based on history, and by noon no sync took place, it would tell MFP you'd burned 1200.
MFP of course would see 1200 at noon, half day, and estimate 2400 also.
If your MFP estimated daily burn had been say 2000, then you'd get a 400 cal adjustment.
Fitbit - MFP - logged exercise = adjustment + eating goal

The problem comes in where the day by the device is really 1000 at noon despite no sync (so better would be 2000 for day). So indeed 400 over what it's looking like.
Say you sync at 6 pm though and day progressed as normal, burning 1500 at 6pm.
Fitbit 1500 sent to MFP, MFP 1500 @ 18:00 hr = 2000 daily Fitbit
2000 - 2000 = no adjustment.

So there are several syncing scenarios combined with when workouts are that could really foul up the best that can be done, leaving huge adjustments one way or another.

That's actually a pretty good adjustment amount, not too large, and small enough you can wait until after dinner and before bed to decide if you want a small snack, depending on what's really left at that point.

But if you sync through the day, then disable Fitbit's Calorie Estimation - adds another layer of estimating not needed.
With it disabled, Fitbit assumes an almost sleeping calorie burn day until a sync proves otherwise, and that is reported to MFP to do math with.

Me neither, I don't have that setting in my Preferences. I just created my account couple weeks ago.

Is that in the app or the web account you are looking for that setting?

Because via the website - Settings - Personal Info - Preferences section still has Calorie Estimation.




You can also get to it under Log section - Food tab - Food plan section - Settings icon gives option for Daily Calorie Estimate Setting for Personalized or Sedentary.
Sedentary means disabled.

I will keep that in mind that on accounts at some point they must have removed it for easy access. Because I hate trying to describe the Food log section.