lose it compared to mfp??

MFP expects you to add in and then eat back your exercise calories - other sites usually include them. So if you exercise even a minimal amount you'll easily get to that 100ish calorie difference and it's all equal.

All calculators use slightly different formulas...that's really not a substantial difference in the grand scheme of things. All of these calculators are just good starting points...nobody has calorie requirements of exactly XXXX calories per one of these calculators...you have to make adjustments as per real world results.

Add to that, different calculators use different methods...for example, MFP uses the NEAT method whereby exercise calories are accounted for after the fact when you log those calories and get them to "eat back"...other calculators that utilize the TDEE method will include some estimate of your exercise calories up front in your activity level...thus they are included in the number from which your cut for weight loss is taken. You also have to take into account rate of loss...2 Lbs per week with MFP is a lot faster than a TDEE - 20% cut...about 500 calories difference between the rate of loss right there alone.

Here's an example of both methods using my numbers.

MFP gives me a calorie goal to lose 1 Lb per week = 1,850 calories
IIFYM gives me a calorie goal to lose 1 Lb per week - 2,245 calories

What's the difference...on average I burn around 400 calories per day in exercise...those calories are already included in my IIFYM calculated calorie goal...they are not included in MFP's goal.

Pick one, go with it, make adjustments as necessary.

All I know is that I'm pretty good at entering my food and exercise accurately, and my weight coincides almost exactly with what MFP predicts.