Fitbit calories burned - is this generally accurate?

A recent University study had participants wear 12 different trackers and had them in sealed rooms so they could measure calorie burn. Most trackers actually underestimated calorie burn. I basically use mine to track activity and to make sure I keep up a certain level. I don't count on accurate calorie burns.

My FitBit is very accurate for me. However, your number does seem high if it were for me. If you are heavier, though, it could be accurate. I weigh 140lbs and burn about 90 calories a mile jogging (that would be 90 calories every 1.61k) so I'd have burned more like 350 calories on your run. However, if you weigh quite a bit more, that could be accurate for you.

I find mine to be pretty accurate as well, but I only eat 3/4 of my exercise calories back just in case.

It is probably relatively accurate for that duration of time, but as zyxst pointed out, it includes your BMR. If you want the number of calories you can log in MFP, you need to subtract your BMR from those. So, for example, my BMR is about 2,200 calories per day. That is 2,200 / 24 = 91.6 calories per hour. 42 minutes is basically 2/3 of 1 hour, so that would be roughly 60 calories of BMR counted in those 643 calories. So, you could add 580 calories as exercise calories. Body weight, elevation change, fitness level, and stride all will affect the actual number of calories you burned. I created a spreadsheet which I use for logging my walking on my treadmill. I found some equations which determine calories burned based on O2 consumption of muscle moving 1kg of weight 1 meter horizontally and vertically while walking, and another based on running. Using that equation, the incline of the treadmill, the duration of the walk, and the distance, I calculate the number of meters moved horizontally and vertically and use my body weight from that day to derive the calories burned. It typically reports a number much higher than the treadmill reports (which seems to use the same equations based on 150lbs of body weight) but a fair bit lower than my MyZone heart rate chest strap monitor reports.

Running, jogging, and walking are all very different in terms of calorie burn because of the vertical weight movement component. When you walk, you are mostly just moving your body weight horizontally. When you jog, there is additional vertical movement of your body weight. When you run, there is considerable vertical movement of your body weight with each stride. All of these effects are compounded when you also have an elevation change involved. This is why heart rate monitors are so useful in determining calorie burn. By watching heart rate, you are basically already factoring in these differences. Unfortunately, they are not as accurate as the equations tend to be.

Mine seems fairly accurate and I have been using mine since this past christmas.