How accurate is fitbit calorie tracking?

[RandomBlazeUser]

 I'm curious to see if there is a way to quantify this. The reason I ask is, I am losing weight however it often doesn't seem to be the two pound/week goal I set. I do cardio for 35-45 minutes 6 days/week, I lift weights for 30-45 minutes 5 days/week, and walk for at least an 1 hour 7 days/week. I have consistently been losing weight, however. Over the 4 weeks according to fitbit I've burned 105,466 calories! Now, I often do measure and weigh majority of food, so I do know my caloric intake could actually be higher than it seems but from my records in the past month I've consumed 59,745 calories.  So according to fitbit my caloric deficit is 45,721 calories for the past month.  This is equivalent to just over 13 pounds worth of calories.  However, according to my scale in these 4 weeks I've only lost 6.4 pounds. Which is still good, and very close to my goal of 2 pounds a week but it is under it, and according to fitbit it is under HALF of the weight I should of lost.  So even saying like, the food I weighed and recorded carefully randomly had 25% more calories i still should of lost 8.8 pounds. It is just discouraging look at these stats as clearly they're very different from what I'm seeing in reality.

[Rich_Laue]

Are you taking into consideration any water you may have drank recently. 

As for quantifying you will need to go to the lab to test this. Lately it has been discovered that calories burnt can be monitored by taking urine samples. 

[RandomBlazeUser]

Water could be a factor, however I'm pretty good at keeping similar levels of hydration etc. I weigh myself before I eat, or drink any water, I don't eat anything dinner however I do drink liquids so there could be slight variance there. Also, I was reading and men can gain between 0.25 - 0.5 pounds of muscle a week naturally, so that could also be another factor as I do lift weights 5 days a week.