Mine are heavily overestimated in the contrary :-D I track every single calorie I eat, so I am quite in the picture :-D . The cause of this is probably the fact that Garmin uses heart rate more than it should. I guess you are very fit person with low RHR, arent you? Unlike me, I am currently very unfit with high RHR.
My active calories (not activity, those seem to be accurate) are drastically overrated because even though I have a low resting heart rate, and I'm fairly fit, the *second* I start doing anything (even standing up brings it up for a few seconds) my heart rate goes up and it says I burned calories doing things like brushing my teeth. So I'm relatively fit but it's still inaccurate because of the way the estimations work, lol. They don't seem to track at all with my heart rate zones, which would fix this issue very easily as I have set them manually, so they DO work in exercises, just not outside of them.
I too track every calorie I eat and my weight, and whether or not I drank more or less water that day, etc. According to Garmin, I should actually be dead from how much weight I would have lost in the two months I've had the watch, it's almost funny. I've just been ignoring all the non-exercise calories. If you haven't checked out changing up your heart rate zones, though, I recommend that! Might fix part of the issue!
