That does seem odd. What is your activity setting in MFP? If it is Sedentary then I'd think you'd have to be really, really inactive the rest of the day to burn 200 calories less that MFP expects a sedentary person to burn despite an exercise session that burned 300 calories. (That's a negative adjustment of 500 calories, partially offset by 300 calories of exercise.) A one mile walk also can't burn that many extra calories (at least 900!). So, something is way off. Have you looked at the heart rate data for the two days? All I can think is that maybe you had very few steps, and a consistently low heart rate on the first day and an elevated heart rate, combined with enough steps to trigger heart rate calorie computations for an extended period on the second day.

Anyway, what I would do is look at the graphs that Fitbit provides that show heart rate for the day and calorie burn for 5 minute segments and see where things are elevated. As an example of what I mean, here's mine from yesterday:





Knowing what I did yesterday, those charts make good sense. The elevated heart rate and elevated calorie burn sections actually correspond with times when I was active. I could also look at steps and see a similar correlation.

Yes, the graphs are from the Chrome web browser. Your phone should provide similar information, even if the graphs aren't identical. I have an Android, not an iPhone, but I would guess that you should be able to get to the heart rate graph by touching the heart rate on the dashboard screen and selecting the desired day and the calories graph by in a similar manner.

Less than half the steps, less than half the distance, truly a bump on a log it appears most of the day.

Yep, that seems normal to lose calories on that day.

But only you can confirm if the busy day was correct.

Look at those blocks of higher calorie burn, Very Active minutes actually, look at the steps graph too.

Were you really doing something intense then?

Or moving arms making lunch or something else?

It certainly looks like you were very inactive on Monday (few steps, low heart rate outside of morning exercise) and much more active on Tuesday (lots more steps, relatively high heart rate for extended periods). However, I wonder if that meeting you attended might have thrown things off. It may be that your heart rate was elevated during the meeting for reasons other than burning calories. Did you walk around much during the meeting? Or did you move your arms a lot while sitting (Fitbit tries to distinguish between moving arms and steps, but can be fooled). Was it a stressful and/or exciting meeting that got your heart rate up even though you weren't moving around a lot? My guess is that your Fitbit got fooled somehow. If meetings like that are a normal part of your days then you'll need to figure it out to avoid having Fitbit seriously overestimate your calorie burn. In the meantime, I'd avoid eating all those extra calories.

Look at your steps time very carefully - was it the time of walking from the train - or actually the train ride had high steps too?
In which case false steps - so device settings may be prone to seeing steps when there are none.

As evidenced by hard gestures at the meeting, and elevated HR.

A agree that steps seems high while on the train, unless you pace while riding.

If you look at your bigger daily graph that is in 5 min blocks, at the steps, you should be able to nail the time exactly as to that hour train ride, and if steps and calorie burn were higher than non-moving time while sleeping say.