I don't understand my fitbit??

I'm not quite sure what you mean? Do you mean the calorie forecast for the rest of the day? This can change because it's making an estimate based on how active you have been during the day (it assumes your activity level will be more or less constant). So if you suddenly sit down for 5 hours after a huge walk, the forecast will continue to decrease to correct it's overestimation. Does this help?

Ohhhh!! Okay, I see now.... So I don't know exactly how much I burned until the next day? I thought it calculated as I took each step...?

It does. If you look at your fitbit device you'll see the calorie display, which is showing your calorie burn based on your steps so far along with your BMR. When you log onto the app, it'll use this data to make an estimation for your calorie burn for the whole day. This can go up or down depending on your activity level as the day goes on. If you're active in the morning but sitting around all afternoon, you'll probably see it drop when it realises you're not maintaining your activity level from this morning

What I have done with my Fitbit is disabled the calorie estimation. It will start you off with a very low amount for the beginning of the day instead of estimating your calorie burn for the day and going up or down. This way instead of suddenly jolting downwards or upwards, it is only really going upwards for me. So I wake up in the morning and it generally says I have about 300 calories or so to work with based on how much I have burned so far in the day (sleeping, whatever). Which is the perfect amount for a breakfast, and then I head to work, do some walking on the way and it gradually gives me more as the day goes on. I found setting up my FitBit like this was the best way. When it was estimating my calories to work with right off the bat I wanted to eat them immediately, and then saw "Crap, no... I didn't exercise enough, it's lowering!". Heh.

What I have done with my Fitbit is disabled the calorie estimation. It will start you off with a very low amount for the beginning of the day instead of estimating your calorie burn for the day and going up or down. This way instead of suddenly jolting downwards or upwards, it is only really going upwards for me. So I wake up in the morning and it generally says I have about 300 calories or so to work with based on how much I have burned so far in the day (sleeping, whatever). Which is the perfect amount for a breakfast, and then I head to work, do some walking on the way and it gradually gives me more as the day goes on. I found setting up my FitBit like this was the best way. When it was estimating my calories to work with right off the bat I wanted to eat them immediately, and then saw "Crap, no... I didn't exercise enough, it's lowering!". Heh.

I didn't know I could do that.. That sounds like a way better system for me!! How do I disable that? I don't like the uncertainty of it going up and down

Go to the website, go to that kind of cog wheel thing in the top right, pick Settings, then in Preferences disable Calorie Estimation.

It might still go a tiny bit down sometimes (not really by much, less than 50 for me usually). But not as much as it did before when it was estimating the whole day. But generally it just goes upwards. You'll sync it one hour, forget about it, be hungry and sync and be like "Ah cool, it gave me 100 more to work with for my day".

I will generally look at the FitBit App for how many calories I can eat based on the amount I've burned so far. So I'll look at it and be like "Ah, it's saying that as of me waking up at 6:00 am I have about 300 to work with... let me shove my mouth with food!". Whereas MyFitnessPal just gives you that 1200 for the whole day, I find looking at the FitBit App helps me kind of spread my meals out during the day perfectly based on how much or little I have exercised. It helps me balance a bit more.

I don't know if what I said made any sense, but it's kind of hard to explain I guess, lol.

But yeah, I use MyFitnessPal to enter food and exercises, because that syncing is so much easier than using FitBit's stupid food log, oh my god. That thing has NOTHING in it. So awful. :P

I use a fitbit flex, and it doesn't always log my activity accurately if I'm doing something where my arms don't swing (like pushups, etc.) so I rely on my heart rate monitor to log my exercise when I want to know my accurate calories burned. Otherwise, I love the fitbit.

On the Fitbit site you can switch up some settings ... you can set your food plan to a set calorie limit (that doesn't change with exercise), or instead of the personalized, go with the "sedentary" setting which as someone else mentioned, start you out low, and has you "earn" calories with your activity (similar to MFP).

Also, if you log exercise manually on MFP, that will come out of your Fitbit adjustment. If you exercise and get a Fitbit adjustment, then log the activity on MFP ... you don't get to keep both, that would give you double credit. So whatever you logged as your calorie burn manually will come out of the Fitbit adjustment. I don't ever log anything on MFP anymore, there were too many problems (the time wasn't transferring correctly to Fitbit, so there often would be double credit). I try just to let my Fitbit count for most activities (walking, jogging, even elliptical and workout DVDs). I do manually enter bike rides and some weight lifting sessions.

Your setting (sedentary/active) on MFP will also impact your Fitbit adjustment ... if you say you are active or even lightly active, you may not see any Fitbit credit come across because MFP is already assuming some level of activity. It's not until you exceed that amount that you'll see a credit. I set myself to sedentary on MFP to start with a low calorie estimate and then to get a Fitbit adjustment I can compare day to day.

On the Fitbit site you can switch up some settings ... you can set your food plan to a set calorie limit (that doesn't change with exercise), or instead of the personalized, go with the "sedentary" setting which as someone else mentioned, start you out low, and has you "earn" calories with your activity (similar to MFP).

Also, if you log exercise manually on MFP, that will come out of your Fitbit adjustment. If you exercise and get a Fitbit adjustment, then log the activity on MFP ... you don't get to keep both, that would give you double credit. So whatever you logged as your calorie burn manually will come out of the Fitbit adjustment. I don't ever log anything on MFP anymore, there were too many problems (the time wasn't transferring correctly to Fitbit, so there often would be double credit). I try just to let my Fitbit count for most activities (walking, jogging, even elliptical and workout DVDs). I do manually enter bike rides and some weight lifting sessions.

Your setting (sedentary/active) on MFP will also impact your Fitbit adjustment ... if you say you are active or even lightly active, you may not see any Fitbit credit come across because MFP is already assuming some level of activity. It's not until you exceed that amount that you'll see a credit. I set myself to sedentary on MFP to start with a low calorie estimate and then to get a Fitbit adjustment I can compare day to day.

This is especially important. If you go for a run and log it on MFP for say, 3PM - 3:30PM, MFP will ignore your Fitbit cals from that time period, since the Fitbit logs calories/steps by time.