I'm using my Fitbit by itself since I don't possess a working computer. Anyway, my burn yesterday according to my Fitbit was 1787. If I keep getting similar numbers throughout the week and then average them together, should I drop my activity level setting and recalculate my TDEE? No way I should be eating 2000 calories if I'm only burning 1800/day, right?

I think I would wait a week until you get am average and see. What kind of workouts are you doing? What are your stats?

I'm 35, 5 ft 1.7 in, 120 lbs. I usually do an hour of weights every other day alternating with an 60-90 min on the treadmill every other day, I do this 5-6 days/week. I do go for walks with my kids (usually pull the younger two in a wagon = over 100 lb load) for around 40 min. I mow the yard an hour every other week or so. Otherwise just washing dishes, going up and down stairs to wash laundry, grocery shopping, etc is all the activity I get. Chasing down the 2 year old now and then, lol.

Ok, I don't trust the fitbit then...becaue I do less than you and my activity level is moderate. I wouldn't drop the calories.

I use fitbit but also use HRM to for workout part. so I usually add how many calories i BURN according to my hrm to MFP, AND MFP will sync to my fitbit.

I use a fitbit too...you have to remember that exercise that does not involve stepping is not going to be accurately calculated in your fitbit calorie count for the day--so fitbit's calorie burn number is accurate for your walking, mowing and running around the house, up/down stairs, etc. But it will not give you an accurate calorie count for that hour of weight training--you can actually override on your fitbit dasboard online by clicking on "log activity" ...then I believe it asks you for the time you did the activity and the calories burned--it then adds those calories to your total for the day (and overrides what it had previously calculated for you). I hope this makes sense! Alternatively, you can just do it mentally...i.e. fitbit says I burned 2000 calories today, but I know my (non-stepping) weight traiing burned at least 200 calories (I use an HRM but you can also use MFP's calculator to get an idea) so just remember that you actually burned 2200 that day. That's what I've been doing. I've been stalking the EMTWL board for a long time now and I think the generally philosophy is it's better to overestimate than to underestimate the amount of calories you allow yourself to eat when you are doing that TDEE - 15% calculation. You can always tweak downward a tiny bit if you need to (after giving it 4 weaks or so).

And a second one more thing ...just re-read your post and you say that you are using fitbit alone (without a computer). You have to also remember that fitbit calculates your daily calories through midnight. So if you check it before you go to bed at night and it says 1800 (or whatever) you're still "burning" BMR-wise until midnight. For me, my sleep time (not wearing fitbit) is automatically 50 cals/hour (so I guess my fitbit BMR must be 1200/day). So...if you're a busy/tired mom going to bed at 10:00 keep in mind that's another 100 calories to add to your total. If you were using the fitbit dashboard on a computer, you'd be able to check your daily total for the previous day.