I'm sure that Heybales and some of the other more experienced EM2WL people will be along to answer your questions, but I do have a few thoughts.

First, if you are doing the TDEE method, you probably don't want to have your FitBit connected to your diary- it can get really confusing. On the TDEE method for calories, you should eat the same amount everyday, unless you know that you're going to have several days way under your normal activity level.

That said, it seems to me that your FitBit is giving you WAY fewer calories than you've figured out your TDEE to be, and that seems unusual. Are you logging all of your exercise that the Fitbit doesn't count? (like swimming, weights, etc) Could your TDEE estimates be too high? How many calories does the Fitbit tell you that you burn every day? (you can find that on the Log page)

In case it helps, here's what I've done since starting EM2WL. I've lost pretty steadily doing this, in fact I hit my goal weight today.

- I don't have my FitBit and MFP accounts linked together. I do the TDEE method, so I figure out how much I'm burning, and manually enter my calorie goal here on MFP.

- In order to calculate my TDEE, I use the Heybales spreadsheet and the Fitbit website. Enter all your info into the spreadsheet, I use the Fitbit tab, because I feel pretty confident that my calorie burns calculated by Fitbit are accurate. Fitbit tells me that I burn an average of 2200 calories a day. I set my calories on MFP at about 2000 to correspond to that.

- In order to get an accurate calorie burn from the FitBit website, i made adjustments to my height based on the spreadsheet. I also use the FitBit website to track any exercise that isn't step based- for me that means strength training and HIIT workouts. If you use that site to track exercise, then make sure you accurately record what time you did the exercise so it doesn't cancel out the wrong base calories. I like to see my exercise on MFP, but I just enter it was 1 calorie burned, that way it doesn't interfere with my calorie goal.

-Then I occasionally adjust my goals if I notice that my burns on the Fitbit site are changing significantly.

I apologize if any of that was confusing. Feel free to add me or send me a message if you have questions about what I tried to explain!

Editing to add- make sure that you also update your weight on the Fitbit site regularly, and on the spreadsheet. That way the tools will be as accurate as possible.

Yep, unsync.

You can do a method that does allow syncing, but frankly it's much easier to plan your day if you do same number daily, and just use FitBit for encouragement and keeping an eye on TDEE levels.

But I'd trust that more than you picking from 5 rough levels, if it changes much.

Get a couple weeks of normal activity in, see what the average TDEE has been on FitBit's site, and do your 15% off that way.

You have a good routine that the FitBit is good at measuring.

So now that is out of the way, I'm just curious on yours, and this may help you understand how it's working normally, or supposed to anyway.

MFP is looking at what it calls maintenance calories, you might say non-exercise TDEE.
They calculate that with BMR x an activity factor based on your choice in setup of Sedentary, Lightly Active, ect.

What did you select there?

What they calculated is shown in My Goals - Your Diet Profile - Calories Burned From normal daily activity. What was that amount?

Don't be freaked out by rest of the figures there, the math is off as soon as you went to manual eating goal that included exercise, which they aren't aware of. So they are taking maintenance with no exercise, minus eating goal with exercise you entered, which may not be negative.

Anyway, they compare the maintenance calories with what FitBit reports, lets just say end of day if you synced once.
If your FitBit TDEE comes back to MFP and is less than maintenance calories, you burned less than they estimated.
So if your eating goal was calculated maintenance minus 500, but FitBit maintenance ended up being 100 less than planned, you get negative adjustment and to keep the 500 deficit, you eat less.

But if you exercised, then that compare would show your maintenance was actually higher for that day, positive adjustment would come across, and to keep the 500 deficit, you eat more.

If you log the exercise on MFP, even if exactly the same calorie burn as FitBit showed it to be, instead of an adjustment, it's already increased your maintenance for that day, just as it normally would, and you eat more.

So as LH was talking about, there are ways to do the more reasonable deficit based on % off rather than block calories, and keep an adjustment aspect to the day, and keep the FitBit synced, but usually easier to unsync.

Ok, I found it. I was set at the highest activity level. What on earth? I've corrected to closer to reality and it's slightly lower now than my Fitbit's average TDEE. I'll have to see how that affects the whole calc now, since I've not yet unsynced. (I rather liked the fitbit dashboard showing me the calories in/calories burned tables)

I have the fitbit force, I have mine synced to show negative calories, it makes me move more during the day! The negative is the worst in the morning! Don't eat less just Use it to your advantage and take an extra walk! Instead of it dictating your intake let it motivate you to move!! (I too like the dashboard showing the calories burned! And steps! )